[] TL: RADIATION MONITORING. An introduction. (GP) SO: Greenpeace UK DT: 1988 Keywords: nuclear power radiation weapons uk europe greenpeace groups gp / [part 1 of 5] By Paul Hayward and Don Arnott. 1988 UPDATED VERSION Produced by Greenpeace U.K. Nuclear campaign. Available from: Greenpeace U.K. 30-31 Islington Green, London N1 8XE. Price 3.5 Pounds Copyright Greenpeace U.K. First Edition, 1987 Second Edition, 1988 INTRODUCTION. Following the Chernobyl disaster there has inevitably been a steady growth of interest in radiation monitoring. This booklet is a practical introduction to the subject. Since the subject of radiation protection is a complex one a substantial introduction to its essentials is given. However, since it would be impossible to include everything necessary in this small publication, a book list for further study has also been compiled. At a more practical level we have compiled information which should help people to plan suitable programmes, cost them and get started. The most important item is a list of manufacturers of suitable equipment. The equipment is described and its suitability or otherwise for specific monitoring requirements is indicated. The prices given were correct at November 1987, when the whole booklet was updated. This information has mostly been summarised from manufacturers' own catalogues, and so its inclusion here naturally does not imply any warranty on the part of Greenpeace as to its suitability for any particular application. We have tried as briefly as possible to indicate where to go for what and intending users should make further enquiries of the manufacturers whom they select. Many more monitoring groups have come into existence since Chernobyl, some are independent and others are operated by local authorities. We have listed all that have come to our notice, with the result that those intending to start will often be able to make contact with somebody nearby who is able to give advice. This list will be updated as opportunity offers. We would like to thank the following for their invaluable assistance: Jo Fuller Dr Barry Lambert. Peter Burgess N.R.P.B. Adrian Silvertown Bernard Wilkins N.R.P.B. Geralt Jones. Dr Martin Courtis. George Pritchard. Dr. P.W. Roberts. CONTENTS ESSENTIAL SCIENTIFIC INFORMATION. Radioactivity Radiation Units Background Radiation Radiation Monitoring Equipment, how it works SETTING UP A MONITORING PROGRAMME. What sort of Monitoring ? How to choose Monitoring Equipment Equipment, Manufacturers, costing the programme RUNNING THE PROGRAMME. Use and Care of equipment Contamination Monitoring Measurement of the Gamma Dose Rate Exact Sample Measurement Local Authority and Independent Monitoring Groups APPENDICES AND TABLES. APPENDIX 1 Calculating the gamma dose rate APPENDIX 2 Some Environmental Factors which can influence the Gamma Dose Rate Equipment Comparison Chart Radiation Units: Summary Radiation Units: Tables Table of Radionuclides Key to Monitoring Procedures Book list Radiation Monitoring Groups Survey Form RADIOACTIVITY All matter is made up of atoms. These cannot be broken up by chemical means and, linked together as chemical compounds, they form all the substances - solids, liquids and gases - which surround us. Each atom is made up of a nucleus, itself composed of protons neutrons, surrounded by a cloud of electrons. The protons positively charged, the electrons negatively charged - so that atom as a whole is, in its normal state, electrically neutral. The electrons are responsible for the chemical behaviour of the atom. The number of protons in the nucleus is called the Atomic Number and it determines which element an atom belongs to. For example, the Atomic Number of Iodine is 53 - so all those atoms containing 53 protons are Iodine atoms. But the number of neutrons which may be associated with these 53 protons can vary, thus giving rise to different forms of Iodine, known as isotopes. All isotopes of an element are naturally identical in their chemical behaviour and our bodies cannot tell them apart. Any given isotope is identified by its Mass Number, which is simply the total number of protons and neutrons in its nucleus. Thus (to follow the Iodine example) amongst the isotopes of Iodine we have Iodine-127, I-131, I-132 and many others. Some combinations of protons and neutrons give stable isotopes, as with I-127 above. In other cases (e.g. I-131, I-132) the combination is unstable i.e. radioactive. Unstable isotopes are variously known as radionuclides, radioactive isotopes or radioisotopes. Unstable isotopes decay into stable forms by emitting very energetic and dangerous radiations, which we shall describe later. This phenomenon is called radioactive decay or radioactive disintegration. Some radioisotopes decay into a whole series of radioisotopes of other elements, giving off radiation at each step before finally reaching a stable form. Two such series are the Uranium and Thorium series, each of which occurs naturally. Each radioisotope decays in its own characteristic fashion i.e. it always emits the same type or types of radiation, and at the same energies. It also decays at a constant rate, which cannot be altered by any known means. This rate, known as the half- life, is the time taken for half of the atoms of that isotope originally present to decay. Since confusion can arise over this we will illustrate once more by following our Iodine example. The radioisotope I-131 has a half-life of 8 days which means that after that time half of the quantity originally present has disappeared. After a further 8 days it would seem that, on first consideration, the remaining half would also have gone; but that is not what happens. Instead, half of what remains after the first 8-day period has decayed i.e. what is left is still one quarter of the original. In practice this means that a given radioisotope will have to decay through several half-lives, before its radioactivity is reduced to negligible levels. Half-lives can vary, according to the isotope, from seconds to millions of years. At the end of this booklet there will be found a table of some of the most important radionuclides, showing their half-lives and modes of radioactive decay. In nuclear reactors, atoms of Uranium are split by a process known as nuclear fission. When each atom splits it produces two new atoms known as fission products and a quantity of energy. This is in the form of radiation, and kinetic energy of the fission fragments, which becomes heat. This heat is used to produce steam, which then drives turbines to generate electricity. The fission products produced in the reactor are intensely radioactive. Amongst them are Caesium 137 and 134, Strontium 90, and Iodine 131. Reactors are designed to contain these fission products but if they do escape from the reactor in an accident, or deliberate release, they can give rise to serious health effects (cancer, leukaemia etc.). Another class of radioisotopes which may be released from reactors are Activation Products. They are produced when neutrons from the fission reaction cause atoms in the reactor structure and coolant to become radioactive. They too can become a source of public radiation exposure. Plutonium radionuclides are also produced in the reactor by neutron absorption in the Uranium fuel. In simplified terms, the radiation given off by radioactive isotopes is capable of transferring some of its energy to the electrons surrounding the nuclei of atoms of ordinary matter. These energetic electrons break away from their atoms to become free electrons; the remaining atom thus acquires a positive charge and is known as a positive ion. This process is known as ionisation. The radiation is described as ionising radiation in order to differentiate it from other forms of radiation, such as light or radio waves, which do not normally cause ionisation. Each charged particle initially produced has sufficient energy to ionise several hundreds of ordinary atoms lying along its path. It is this ionising effect which causes the damaging biological action of this type of radiation. Many natural and man-made radioisotopes tend to concentrate in particular body tissues. For example, radioisotopes of iodine are concentrated in the thyroid gland : Strontium-90, which is chemically similar to calcium, naturally concentrates in the bones. There are three main types of Ionising Radiation - ALPHA PARTICLES are usually given off by the nuclei of the heavier radioisotopes such as Radium and Plutonium. They are emitted with energies of about 5MeV (five million electron volts). They leave a short dense trail of ionisation, and are capable of penetrating much less then a millimeter in solid matter. They are stopped by the dead outer layer of our skin, but there is a major health hazard if isotopes giving off alpha particles are taken into the body by ingestion or inhalation. Alpha particles are 20 times more biologically damaging than the same dose of beta or gamma rays. Alpha particles are not easy to detect in the environment because a thin layer of water, dust or oil will absorb them completely. BETA PARTICLES are high speed electrons emitted from the nuclei of many natural and man made radioisotopes. The beta particle is ejected from the nucleus at near the speed of light. Some beta emit tiny isotopes give off low energy beta rays, some give off high energy beta rays. Low energy beta rays will not be able to penetrate the skin, but high energy beta rays are capable of penetrating up to about a centimeter or so in solids and therefore of penetrating and damaging the skin. They are less heavily ionising than alpha rays but are also a hazard if isotopes emitting them are eaten or inhaled. Some beta emitting isotopes give off gamma rays as well. GAMMA RAYS are true electromagnetic rays (like light or radio waves). They are similar to X rays but usually of a higher energy. They are given off by many, but not all, radioisotopes. Many are very penetrating, and can only be attenuated by a large thickness of concrete or lead etc. They can penetrate the whole body and are the dominant form of external radiation. As in the case of alpha and beta emitting isotopes it is a hazard if gamma emitting isotopes are ingested or inhaled. RADIATION UNITS. There are two different types of radiation units: Units of Activity (or radioactive quantity), and units of radiation Dose. A) Units of Activity. As already explained ionising radiation in the form of gamma rays and charged particles is given off by unstable nuclei when they decay. The concept of Activity is used to describe the number of these radioactive disintegrations occurring over time. (i) The Becquerel The S.I. unit of Activity is the Becquerel (Bq). One Becquerel is simply one radioactive disintegration per second. Since the Becquerel is a very small unit multiples of it are often used. i.e. one Kilobecquerel (1KBq) - 1000 disintegrations per second. Radioactive contamination of food and surfaces is measured in Becquerels per Kilogram and Becquerels per Square Centimeter respectively. (ii) The Curie. The previous unit of activity was the Curie (Ci). It originated at the time when Radium and its daughter products were the only important and strongly radioactive materials in regular use. One Curie (Ci) = 3.7 x 10 10 radioactive disintegrations per second i.e. thirty seven thousand million Becquerels. This definition was adopted because it represents the radioactivity of 1 gram of radium in equilibrium with the radioactive daughter products, beginning with Radon, into which it decays. More manageable units came into use: the Millicurie (mCi) and the Microcurie (uCi) - respectively one thousandth and one millionth of a curie. Although the Curie is being replaced, its relationship to the Becquerel must be known since many text books still use the old unit. B) Units of Radiation Dose. When ionising radiation interacts with matter and living tissue, it transfers some of its energy to the atoms and molecules causing ionisation and hence chemical changes. The concept of radiation dose was evolved in order to be able to quantify this effect, thus enabling a more precise understanding of the different effects of various amounts of radiation to be obtained. (1) Absorbed Dose The absorbed dose is simply a measure of the energy transferred to the issue or substance in question. The S.I. (metric) unit of absorbed dose is the Gray (Gy). This is a simple measure of energy transfer and takes no account of the different biological effectiveness of alpha beta and gamma radiations in causing damage to tissue. (ii) Quality Factor. In order to take into account this difference in ability to cause damage to tissue the concept of the Quality Factor (OF) is used. It is set at 20 for alpha particles and 1 for gamma rays and beta particles. This is because alpha particles cause more ionisations per unit length of their path through tissue, and hence more biological damage. (iii) Dose Equivalent. The Absorbed Dose in Grays is then multiplied by the appropriate Quality Factor to give the Dose Equivalent in Sieverts (Sv). i.e. Dose Equivalent in Sieverts = Absorbed Dose in Grays x QF. The Dose Equivalent therefore takes into account the fact that Alpha particles are able to cause more biological damage than gamma or beta radiations. One Sievert is quite a lot of radiation. As little as four Sieverts will cause severe radiation sickness and a 50% chance of death if incurred over the whole body. Units of dose equivalent that one is more likely to see with reference to low levels of radiation are Millisieverts (mSv), or thousands of a Sievert and Microsieverts (uSv) or millionths of a Sievert. (iv) Dose Equivalent Rate, This is usually shortened simply to Dose Rate. It is a measure of the quantity of radiation absorbed over time e.g. Millisieverts per hour (mSv/h). (v) Previous System of Units. The former units of Absorbed dose and Dose Equivalent were the Rad and Rem respectively. One Gray is equal to 100 Rads, and one Sievert is equal to 100 Rems. The Quality factor was previously called the R.B.E. (Relative Biological Effectiveness) but its values were the same. So: Dose Equivalent in Rems = Absorbed Dose in Rads x R.B.E. There is a table at the end of this booklet which relates the Rem and Rad to the Gray and Sievert and their respective multiples. Tables of this sort are in use in health physics departments too, as very few scientists are able easily to convert from one system of units to the other. Most scientists were educated at the time when the old units were in use and they still think in terms of Rads and Rems. Other concepts related to radiation dose will be encountered in the literature of radiological protection. They should be understood, but the purpose of including them here is essentially educative. Rarely if ever will those conducting monitoring programmes of the type described in this booklet have the need, or indeed the capacity, to estimate, for example, Man Sieverts or an Effective Dose Equivalent. (vi) Committed Dose Equivalent. When radionuclides are absorbed into the body, they may remain there for periods ranging from a few hours to many years, until they decay away or are eliminated from the body (Radioactive half-life and Biological half-life are used to describe this decay and removal). All of the time they are present in the body they continue to irradiate the tissues. This is taken into account in the Committed Dose Equivalent, which is measured in Sieverts. This an estimate of the whole-body Dose Equivalent delivered to the body tissues over the period of 50 years following the ingestion of a known type and quantity of radioactive isotope. It is, as it sounds, an estimate of the dose one is committed to receive subsequent to such an ingestion. (vii) Effective Dose Equivalent. Some bodily organs are more sensitive to radiation than others. To take this into account the various organs are assigned weighting factors based on estimates of their relative sensitivity to radiation damage. When the dose to the individual organs is measured or calculated it is then multiplied by the appropriate weighting factor to give the Effective Dose Equivalent. This is the dose which if it were applied to the whole body, would produce the same risk of cancer and genetic damage as the separate individual doses to the various organs. The weighting factors to be applied are determined by the International Commission on Radiological Protection (I.C.R.P.) which publishes them in tabular form. Their application, and ultimate significance, are complex questions beyond the scope of this booklet. (viii) Collective Dose Equivalent. When exposures to large populations need to be estimated the term Collective Dose Equivalent is used. This is simply the average radiation dose to an individual in the population under study multiplied by the number of individuals in that population. This gives an estimate of the total dose received by that particular population. The unit used for this concept is the Man Sievert. C) Relationship between radiation dose and radioactive quantity This is never simple to determine and is in practice frequently impossible to do accurately though useful estimates may be made. With regard to radiation received externally by the body: if one knows the duration of the exposure, the distance of the body from the source, the area of the body exposed (the 'field' in radiotherapy) and the energy and type of radiation involved, it is possible to calculate the absorbed dose received with good accuracy. But for other dosages received externally, that is from the alpha or beta particles, the accuracy falls dramatically. Firstly, these radiations are strongly absorbed even by air so that even minute changes in the distance between source and body can strongly influence the result. Secondly these radiations are even more strongly absorbed by skin, which varies in thickness from place to place, the outermost cells being dead anyway. When it is a matter of calculating the dosage received from radioisotopes distributed internally the problem (except in the case of a sealed source deposited in a known position) becomes effectively insoluble, although informed and useful estimates may often be made. The biggest factor involved is non-uniformity of distribution of the radioactivity, which is apparent not merely between one tissue and another but also within individual tissues and even their individual cells. Other, and more manageable factors which influence such calculations are the half-life of the radioactive material and its residence-time ('biological half-life') in the body in the particular tissue or organ. Chemistry also plays a part; for instance radio iodines, we are used to saying, are selectively accumulated by the thyroid glands but this is true only if the radio iodine is present in inorganic form (as Iodide). If it is organically bound it is more likely to end up in the liver. It is from considerations such as these that the International Commission on Radiological Protection (ICRP) derives dose- limits, both internal and external, for the protection of occupationally exposed workers and the public at large. The voluminous tables of figures convey a sense of accuracy which is usually partly spurious; the correct way to use these tables is to keep exposures as far below the quoted levels as possible. [] TL: RADIATION MONITORING. An introduction. (GP) SO: Greenpeace UK DT: 1988 Keywords: nuclear power radiation weapons uk europe greenpeace groups gp / [part 2 of 5] BACKGROUND RADIATION We are all constantly exposed to radiation from natural sources such as cosmic rays, gamma rays from radioactive isotopes in the earth 's rocks, gamma and beta rays from naturally occurring Carbon 14 and Potassium 40 in our own bodies and radiation from Radon and its daughter products breathed in from the air. This is called natural or background radiation. Since the 1950's some of the background radiation is due to fallout from nuclear weapons tests. The biggest single contribution to background radiation arises from rocks such as granite which are naturally radioactive, and gives rise to gamma rays and radiation from Radon gas and its decay products. Cosmic rays increase with altitude but the effect is very small in the U.K. The average U.K. background dose from all these sources is about 2 mSv/yr. (2 thousandths of a Sievert per year ). As there are 8,760 hours in a year, the normal U.K. exposure rate is about 0 .0002 mSv/hr, (= 0.2 microSv/hr, 0.2 millionths of a Sievert per hour). This natural background level is not small, it is the equivalent of about 30 ,000 ionising rays and particles passing through our bodies each second. We and other living things are being fairly strongly irradiated by natural sources of radioactivity. But the fact that it is 'natural' does not mean that it is safe. The natural radiation background produces its quota of death and injury to living things every day. Medical X-rays, though not background, are a major part of the total public radiation exposure. Although in many cases X-rays can be a useful and life saving diagnostic tool, this is not always the case. Often they are used in a routine manner, 'just to be on the safe side ', (i.e. regular six monthly dental X- rays). It is only in recent years that the X-raying of pregnant women has been abandoned due to the risk to the unborn child. Potassium 40. Potassium 40 is a very common radioactive isotope. It is present in many of the foods we eat, and therefore if measurements of contamination in food are attempted it must be taken into account. This is only a real problem with some scintillation detectors which do not have the ability to discriminate between different energies of gamma rays, and hence different radioisotopes. The Mini instruments food monitor and the Berthold becquerel monitor are of this type. Some foods, such as dried apricots for example, contain quite a high level of Potassium. Since a small fraction of all Potassium is radioactive Potassium 40, these foods may be radioactive enough under normal circumstances to give a detectable reading. Food tables giving the nutritional content, including Potassium, of foods may be of some help in allowing for this. Potassium in foods will have a gamma activity of about 3.5 Becquerels per gramme of Potassium present (e.g. if a food contains 2 grammes of Potassium per kilogram, then it will have a gamma activity of about 7 Becquerels per kilogram). Potassium Chloride (such as in commercially available salt substitute) has a gamma activity of about 1.8 Bq/gram. About 11% of the rays given off by Potassium are gamma rays, and the rest are beta particles. So the beta activity of Potassium is about nine times its gamma activity. Potassium Chloride can be used as a source to test your radiation monitor as it gives off gamma radiation which is similar, in terms of counter response, to that given off by potential contaminants such as Caesium 137 etc. There is no significant danger in eating Potassium Chloride which will always contain the same small amount of radioactive Potassium 40, because our bodies already contain quite a lot of Potassium (about 140 grams) and any additional amount is rapidly excreted. Food tables giving the Potassium content of most common foods can be found in the whole food cookbook "Laurels Kitchen" published in paper back by Bantam Books, or in food tables such as those published by H.M.S.O. in Britain. RADIATION MONITORING EQUIPMENT - how it works. All radiation monitoring equipment consists of two basic components. Firstly there is a radiation detector capable of turning ionising radiation into electrical impulses which can be recorded. Secondly there is a "box", essentially electronic, which both supplies the radiation detector with the voltage it needs and records the signals it emits. Sometimes both units will be found together in the same box. In other equipment the radiation detector will be separately mounted, for example as a probe which can be easily moved around when looking for radioactive contamination. The three main types of radiation detector most often encountered are Geiger-Muller tubes, Scintillation Counters and Ionisation Chambers. Of these, the Geiger-Muller tube is most commonly found for several reasons; amongst them, versatility of design, relative robustness, ease of operation and replacement and, not least, its relative cheapness. These three detectors will now be briefly described. A Geiger-Muller tube is basically a very simple device. It consists of a sealed cylindrical tube containing a suitable mixture of gases and two electrodes. One of these, the anode, is given a positive DC charge at a carefully chosen voltage. The other, the cathode, is earthed. The gas in between these electrodes does not normally conduct electricity but when an ionising ray or particle enters the tube it ionises the gas filling. The electrons so produced are accelerated to the anode thus producing an electronic pulse. It is these pulses which are recorded in one or more ways depending on the instrument e.g. light flashes, audible clicks, a deflection on a meter or a number on a digital display. Some Geiger tubes have a thin end 'window' (often made of mica). This enables alpha particles and low energy beta particles, which would otherwise be stopped by the metal case of the tube, to pass inside and be detected. Tubes with metal cases but without this window will detect only gamma rays. They may also be able to detect some high energy beta rays, but they will not be able to count them with any accuracy. There are "compensated" and "uncompensated" Geiger tubes. Uncompensated tubes have very different detection efficiencies for gamma rays of different energies. Energy compensated tubes contain filters to level out this variation to some extent, giving a more linear response to certain energies of gamma rays. Most Geiger tubes are, in practice, only one or two percent efficient for the detection of gamma rays. This is due mainly to some rays going straight through the geiger tube and not producing a detectable pulse. However geiger tubes with a thin end window may be 5-20% efficient for beta particles. A Scintillation Counter operates on an entirely different principle: that of turning ionising radiation into flashes of visible light. It consists of a crystal of a substance such as Sodium Iodide which will scintillate in this way. This is attached to the window of a device called a photo multiplier which converts the light-flash into an electric pulse and then amplifies it until it is large enough to be recorded, essentially in the same way as for a GM tube. In addition, scintillation counters differ in one very important way from GM tubes. The latter are non- discriminating, "all-or-none" detectors which give the same size of signal irrespective of type or energy of the initiating radiation. But a scintillation counter can discriminate in these ways and may thus be used not merely to detect radiation but also as an analyser, since it can discriminate between one radioisotope and another by means of the radiation energies characteristic of those radioisotopes. But to do so requires special electronic equipment which will be described later. There are many different types and sizes of scintillation counters. They are usually used to detect gamma rays, but can be specially designed to detect alpha or beta particles. The larger the crystal is the more sensitive it is to high energy gamma rays, but very thin crystals are used to detect alpha and beta particles. There are also "well type" scintillation counters in which a sample is placed into a hole inside a large crystal; this increases the detection efficiency, by detecting rays emitted from the sample in almost all directions. For gamma rays in particular scintillation counters are very efficient indeed, usually more so than the average GM tube; they therefore may be the most efficient way of detecting low levels of radioactivity. Detectors made from a Germanium and Lithium compound are the best for discriminating between isotopes emitting gamma rays of very similar energies. Germanium/Lithium detectors are semi- conductor devices and have to be kept at liquid Nitrogen temperatures to operate; they are very expensive. The third type of radiation detector, the Ionisation Chamber, may be dealt with more briefly since its applications in the general field of radiation monitoring are relatively few and specialised. GM tubes measure individual pulses - an ionisation chamber measures an ionisation current - the sum of many pulses arriving almost simultaneously. In skilled hands and for special purposes ionisation chambers are invaluable; but in the field which interests us their most frequent use is as personal radiation dosimeters. We now turn to the "other half" of the radiation monitor: that part which both supplies electrical energy to the detector and also amplifies and records the signals so obtained. They may be mains or battery-operated, or both. All contain a power-pack which will supply voltage of the sort required by the detector: that is, to the anode of a GM tube or to the photo multiplier of a scintillation counter. There are several ways of recording signals. The most common is to read the deflection of a needle on a meter, which may be calibrated (depending on the instrument) either for measurement of radiation dosage or for radioactivity. The most obvious disadvantage of this method is that it is extremely difficult to obtain a steady reading from a low-radiation field. For greater accuracy, particularly at low levels of radiation, a device known as a scaler is preferable. This adds together the signals received over longer periods of time, which can be preselected (e.g. 1 minute, 10 minutes etc) and is the only method of obtaining statistically significant data. A meter deflection can be, at best, a useful indications but accuracy of measurement, where this is required (which, as will be seen, is not always) requires the use of a scaler. This remains true whether one is considering the measurement either of radiation dosage or radioactive contamination. Many instruments have, in addition, an audible warning (clicks produced in a loudspeaker) or a visible one (light flashes). Both are valuable, but the audible warning is always to be preferred since the human ear responds instantaneously to either increase or decrease in this signal. For work in the field, when it is necessary to pinpoint areas of greatest concern with maximum speed, the instrument chosen should always have audible warning. Scalers which are suitable for use with scintillation counters may in addition have electronic circuits which enable one to take advantage of the discriminating ability of these counters. Such scalers may have a "Threshold" control which sets a lower limit to the energy it will detect, and a "Window" control which sets a band of energies to be detected. This enables one to count only the gamma rays emitted by a specific isotope like Caesium 137 for example. This type of equipment is also called a single channel analyser. Dual channel analysers are able to count two bands of energies separately. Multi-channel analysers are able to display the whole range of gamma ray energies from a sample, split into many individual bands or channels; the more channels the equipment has, the finer the resolution possible between radioisotopes with similar gamma ray energies. This type of equipment is sometimes referred to as a Pulse Height Analyser. Equipment of this sophistication can also be called a Spectrometer, because it displays the spectrum of gamma rays given off by a sample. Spectrometers can enable one to determine precisely what isotopes are present in a sample. Spectrometers may be designed to detect alpha or beta particles, but an alpha spectrometer will only detect alpha particles and a beta spectrometer will only detect beta particles. Alpha spectrometry in particular is a difficult and expensive business, requiring complicated preparation and chemical separation of the sample. Mention should also be made of liquid scintillation counters though largely for the sake of information. Although valuable, this highly specialised and expensive technique really falls outside the scope of this book. In these a sample is placed in a small bottle, mixed with a liquid which scintillates in the same way as the scintillation counters already mentioned. These detectors necessitate careful preparation of the sample. Most of them are capable of running through large numbers of samples and printing out the results. Liquid scintillation counters are able to count low energy beta rays from isotopes such as Tritium, which cannot be detected by geiger tubes or solid scintillation probes. They may also be set to discriminate between different energies of beta rays, and thus different radioisotopes. Trained technicians are usually necessary to interpret the results obtained from equipment of this sophistication. Liquid scintillation counters and spectrometers are used by university radio biology or biological science departments, and the various national radiation protection bodies and regulatory boards, to make very accurate measurements of the radioisotopes present in food and environmental samples. Another form of monitoring device that may be encountered is the Thermo-Luminescent Dosimeter or TLD. This usually takes the form of a small personal dosimeter device. It works on the principle that certain crystalline substances have the ability to store energy in their crystal structure proportional to the dose of gamma radiation they have absorbed. This energy can be released in the form of ultraviolet light when the TLD is heated carefully in a device designed to read the dosimeter in this way. The main advantage of these devices is the relative cheapness and portability of the individual dosimeters. The main disadvantages are the high cost of the machine needed to read the TLDs, the tendency for doses received at the beginning of the exposure period to fade over time; also they can be inaccurate by up to 50 , and cannot record sudden transient increases in dose rate. TLD's only provide an indication of the average dose rate over the exposure period. These devices are used mainly to record the personal dose of workers in the nuclear industry but some local authorities are using them for environmental gamma monitoring by mounting them on posts in the field. Finally, one other monitoring device that may be encountered is the Shade or Tacky Shade. This is a lampshade-like device made from cloth which is suspended from a frame on a pole in the field. In the case of the tacky shade it is impregnated with a sticky material to make particles adhere to it more. The intention is that airborne radioactive materials will stick to the shade which is then collected for laboratory analysis. The shade is burned to an ash in carefully controlled conditions and the residue, which will contain the radioactive materials deposited on the shade during its exposure to the air, as well as those naturally present in the cloth, is analysed in a spectrometer. Results from this type of monitoring are only approximate but are able to indicate if levels of airborne radioactivity are steady or if there is a change due to fallout or atmospheric discharges. Shades are not very efficient for the detection of the smallest of airborne radioactive particles, which may be given off by nuclear power plants, fuel fabrication or reprocessing plants. WHAT SORT OF MONITORING? We will begin with a simple grouping of the various monitoring practices in terms of their function, as follows - a) Area Monitoring by a systematic programme of gamma dose rate measurements conducted regularly at specific locations. This is also known as baseline studies, background studies or environmental monitoring. In such studies field measurements of the gamma dose rate are made in air, often on a monthly or weekly basis. Almost the whole of what they detect arises from fallout deposition and natural radionuclides on the ground beneath the detector. The purpose of these measurements is to prepare a map of the gamma radiation intensity in the area under study. Thus in the event of another Chernobyl-type accident, it will be easy to detect the increase in dose rate due to deposited fallout, something that would be difficult to do with any precision if one had no knowledge of the radiation status of the land before the accident. The monitors usually used for this type of monitoring will not be able to distinguish between radioactive Caesium fallout and naturally occurring gamma rays such as those from Uranium and its decay products in rocks such as granite. Scintillation detectors which would be able to make this distinction are expensive and are rarely used in the field. In order to cover the whole country a large network of monitoring groups all using the same techniques is necessary, so that results from one area can be compared with those from others. From a national point of view these baseline studies are most important and it is hoped that as many independent monitoring groups as possible will participate in them. b) Contamination Monitoring. The need for this arises if there is a suspected leakage of radioactive materials. In normal circumstances contamination monitoring is used to help in the cleaning up of small spill ages of radioactive materials in nuclear plants and research establishments. It would also be essential in the event of more drastic eventualities such as a leak from a nuclear plant, or where unacceptable contamination of a coastline is suspected due to discharges from a reprocessing plant, or in the event of a transportation accident involving nuclear fuel or waste. Field equipment similar to that used for (a) is used. Its purpose is simply to detect areas where radioactive contamination is present at levels substantially above background. It may be necessary to look for contamination due to alpha or beta emitters as well as for gamma emitters. The techniques give a warning which is only semi-quantitative, but this more than offset by the speed with which it is possible to determine whether or not a hazard is present. Further more specialised measures can then be taken. c) In-vivo Monitoring. This is the measurement of radioactivity in a living subject, animal or human. From the standpoint of independent or local authority monitoring groups it is a special case, arising in only one circumstance, but crucially important if that should happen. This is a reactor accident which leads to the release of fission products to the atmosphere, as at Chernobyl. The composition of such a reactor cloud will vary with its age, but in its early life it is certain to contain a predominance of Iodine 131 (half-life 8 days). This is quickly and selectively absorbed by the thyroid glands of human beings and animals. The concentration-gradients are so enormous that its detection in living thyroids could easily become the most sensitive indicator of trouble in the early stages of cloud fallout. More so, for instance, than in rainwater, in which there is no such selective concentration. The radioiodines (Iodine 132 may also be involved) are beta- gamma emitters and the thyroid gland is accessibly situated in the neck and just below the skin. With little adaptation a gamma monitoring tube applied to the neck will detect uptake. Once more the measurement is semi-quantitative but still of great value in an emergency situation of this sort. Repeat measurements on the same subjects will determine whether levels are rising or falling. It is also possible to monitor the radiocaesium levels in sheep by in-vivo means not involving slaughter. It is obviously far better to do so since repeated measurements on the same animal will give a slope, thus indicating whether levels are rising, falling, or staying constant. Government bodies/ such as the British Ministry of Agriculture Fisheries and Food (M.A.F.F.), already do this to some extent, but at present in-vivo Caesium monitoring is beyond the scope of this booklet. d) Exact Sample Measurement. In contrast to the three foregoing, this is a skilled and exact laboratory procedure involving expensive specialised equipment, careful sample preparation and considerable technical ability and experience. Essentially of course it is a specialised case of contamination monitoring. Where an emergency is widespread, as with a nuclear fallout cloud, rainwater, food and numerous foodstuffs will need careful radioactive assay. In addition to that, there are many other circumstances where exact sample measurement is necessary. If such methods are needed, the decision as to whether one employs commercial firms, which are expensive, to assay one's samples or sets up for oneself, requires careful judgment. If a continuing need for sample assay is envisaged, the latter option should be seriously considered. It can be cost-effective very quickly, and it obviously confers versatility and flexibility on the programme. What, then, to monitor? The answer depends very much on what you have in your area. A landlocked rural area with no nuclear installations might well settle for the area monitoring programme only. For a little extra it could also set up for contamination monitoring. The latter is highly desirable because the use of radioactivity for medical and industrial purposes (quite apart from activities connected with the nuclear industry) is so widespread that no area nowadays is free of the possibility of a transportation accident. At the other extreme, the local authorities in a large conurbation which necessarily imports most of its food, some from abroad, should wish to keep an eye on the levels of radioactivity it contains. They could set up for exact sample measurement as a continuing part of their environmental protection responsibilities. In between: areas which contain nuclear establishments, above all reprocessing plants, may wish to make their first investment in contamination monitoring, with exact sample measurement if they can afford it. The first step is to form a first assessment of the potential hazards in the area. The next to familiarise yourself with the equipment available, what it will do and what it will cost. Finally to see who, living nearby, may be able to offer advice or join in a cooperative programme. In order to help in this objective we have listed all of the independent monitoring groups we are aware of later in this booklet. HOW TO CHOOSE MONITORING EQUIPMENT. The first point to understand is that there is no one piece of monitoring equipment that will be suitable for monitoring all types and strengths of radiation. Each different monitor will have its own specialised use. You must always buy the appropriate instrument for the type of monitoring you wish to undertake. It is no use buying a gamma dose rate meter if what you really want to do is to test food for fallout contamination. Food monitors designed for this purpose are available and will do the job, the gamma monitor will not. Before buying any radiation monitoring equipment it is essential to get expert advice on what sort of monitoring programme is most appropriate for the area in which you are based. Only when the individual circumstances and hazards of your area have been investigated and taken into account can any sensible decisions be taken about the purchase of equipment. Some simple equipment for the measurement of gamma dose rate may have some application whatever your circumstances, but the more sophisticated and expensive equipment will have more restricted and specialised uses. Although it is possible to economise by buying an inexpensive radiation monitor from one of the more recent manufacturers, there are definite advantages to having properly calibrated equipment from one of the manufacturers used by the nuclear industry themselves. If one finds a source of radioactivity with a cheap radiation monitor it is very easy for the authorities to assume that the instrument was not properly calibrated and that the results are inaccurate. If one is using instruments which their own health physics experts are familiar with and rely upon, it is much harder for them to dismiss the readings. So if you require accurate results which may be for publication, rather than simply wishing to check for radioactivity as cheaply as possible, just to protect yourself, there are great advantages to buying the somewhat more expensive equipment from well established manufacturers. Whatever equipment you are using, if accurate readings are required it must be properly calibrated by a recognised laboratory. [] TL: RADIATION MONITORING. An introduction. (GP) SO: Greenpeace UK DT: 1988 Keywords: nuclear power radiation weapons uk europe greenpeace groups gp / [part 3 of 5] Gamma monitoring For this a monitor using a gamma sensitive Geiger tube, Ionisation Chamber or Scintillation Detector is necessary. There are many different models available, too many to list here. For some the choice will be limited by price considerations. In most cases it is a case of "you get what you pay for" although imported equipment will tend to be more expensive than that bought in the country in which it is manufactured, due to transport costs etc. The cheapest models are often the least sensitive and have the most rudimentary facilities. The monitors available at less than about 150 pounds will not be able to detect very small fluctuations in dose rate, within the range of normal background radiation. But they may be able to warn of sudden large increases due to nuclear accidents. Models in the 200 to 500 pound range are generally sensitive enough to detect the slight increase in dose rate around nuclear power stations. To get accurate measurements of small changes in dose rate a scaler is needed such as the Mini Instruments 6/80. Instruments of this type are necessary if one wants to make a detailed study of small changes in the dose rate or conduct a Baseline Survey. Contamination Monitoring. Radiation monitors which are sensitive to alpha and beta particles may enable one to detect contamination due to discharges from nuclear reprocessing plants or accidental leakage of radioactivity. The more expensive scintillation type alpha and beta probes such as those from Nuclear Enterprises are very sensitive and, if used with a good scaler, would enable one to detect very low levels of contamination. However, contamination monitoring for alpha and beta emitting isotopes is often more straightforward in nuclear plants, or other man made environments, with relatively smooth flat surfaces, than in the natural environment. Once such isotopes have been washed down into the soil or absorbed by plants they become very hard to detect. Exact Sample Measurement As previously mentioned this equipment is rather expensive. Each piece of equipment will have its own operating method. Guidelines on sample taking methods are given in the section on using the equipment, but more detailed information should be sought from expert sources before purchasing this sort of equipment or attempting to operate it. The simpler food monitors from Mini Instruments and Berthold will be quite able to detect radioactive contamination in food, or environmental samples, due to gamma emitting isotopes at levels above about 40 Bq/kg, but some determination of the normal gamma activity of the sample, due to naturally occurring radioisotopes, must be made. However for more exact determination of the exact isotopes present at least a single channel analyser is required. EQUIPMENT MANUFACTURERS The following pages contain the addresses of all the manufacturers we have contacted so far. They are listed alphabetically. We have tried to advise on which equipment may be suitable for the different types of monitoring which are necessary. All prices are correct as of November 1987, and are exclusive of V.A.T. except where otherwise stated. MULLARD GEIGER MULLER TUBES Many of the Radiation Monitors in this report use Geiger Muller tubes made by the Mullard company. These are usually identified by a four digit number with the prefix ZP i.e. ZP1430. Mullard produce a very good technical handbook which gives the specifications of all their tubes. It is called Technical Handbook, Book Two, Electronic Tubes Part 2B Geiger Muller Tubes. It is very good for comparing the sensitivities of different geiger tubes, or for choosing tubes if you are attempting to improve equipment by fitting a more sensitive tube. Their address is: Mullard Limited, Mullard House, Torrington Place, London WC1E 7HD, ENGLAND. Phone O01 580 6633. ALRAD INSTRUMENTS LTD Turnpike Road Industrial Estate, Newbury, Berkshire, RG13 2NS, ENGLAND. Phone. 0635 30345. Alrad Instruments are the U.K. agents for Victoreen Ltd, 10101 Woodland Ave, Cleveland, Ohio, U.S.A. Phone. 216 785 8200. Victoreen make a range of monitoring equipment, including; The Model 493 Utility Survey Meter, Cost 392 pounds. This is a portable survey meter with a meter calibrated in millirem per hour. It can be used with any of their probes for the detection of alpha, beta, or gamma radiation, depending on the probe used. The meter unit includes an internal check source to confirm the operation of the meter. An audible indication of count rate can be provided with the optional loudspeaker or headphones. The probes range in price from 164 pounds for the 493-50 beta- gamma probe, to 220 pounds for the 489-11OA Pancake probe for the detection of alpha beta and gamma. AUTONNIC RESEARCH LTD. Woodrolfe Road, Tollesbury, Essex, Cl9 8SE, ENGLAND. Phone. 0621 869460. The Model 90 Meter is a versatile gamma survey meter (cost 163 pounds) which can be used with the 911L probe (cost 73 pounds) which uses the ZP1200 geiger tube for gamma detection, or the 921L probe (cost 78 pounds) for beta-gamma detection. The Model 90 is a ruggedly constructed dose ate meter with a meter calibrated in milliRem per hour. It has 4 scale ranges covering from 0.1 to 500mRem/h. It is shockproof and waterproof enough to cope with driving rain. It is therefore a tougher alternative to the more laboratory oriented meter units from manufacturers such as Mini Instruments. Including V.A.T. the total cost of probe and meter unit would be around 280 pounds. They also supply meter units and probes for fixed alarm monitoring applications. BERTHOLD INSTRUMENTS LTD. C.T. House, 1 Maxted Close, Maylands Industrial Estate, Hemel Hempstead, Herts. HP2 7EG. ENGLAND. Phone. 0442 232626. In France: BERTHOLD ANALYSE INSTRUMENTATION. Zone Artisanale des 4 Arbres. 6. rue de Marechal--Ferrant.- F 78990 Elan court. FRANCE. Phone. 33 (1) 30 62 31 12. Or in Belgium: BENELUX ANALYTICAL INSTRUMENT N.V. SA Vaartdic 22. B-1800 Vilvoorde, BELGIUM. Phone. (02) 251 60 10. This German based company produces a wide selection of monitoring equipment including both hand held monitors and lab based equipment for exact sample analysis. One of their latest products is Becquerel Monitor LB 200. This is a simple food monitor, which uses a scintillation detector and it is capable of detecting radioactive Caesium contamination down to around 20 Becquerels per kilo. It needs a sample weighing half a kilo. The machine will calculate the contamination for you in Becquerels per kilo, but it assumes that the contamination is Caesium 134 and 137, it is not capable of differentiating between different radioisotopes, and is similar to the Mini Instruments food monitor in this respect. With a printer for permanent recording of the results it costs around 30,000 francs (Approx. 3,000 pounds), without the printer about 22,000 francs(2,200 pounds). They also produce contamination monitors with a large detector area. JOHN CAUNT SCIENTIFIC LTD Oakfield Industrial Estate, Stanton Harcourt Road, Eynsham, Oxon. OX8 1JA, ENGLAND. Phone 0865 880479. John Caunt manufacture and distribute scintillation crystals and associated equipment. Their SD1 Single Channel Analyser costs 975 pounds and once the price of a 2"x 2" Sodium Iodide scintillation crystal and photo multiplier tube (675 pounds) and some lead shielding (560 pounds) has been added on the total is about 2200 pounds. Because of the lead shielding and the 2" x 2" scintillation crystal, this combination would probably be better than either the Nuclear Enterprises food monitor (which has no shielding or the Mini Instruments one (which has a smaller, less sensitive scintillation crystal and is not able to differentiate between different radioisotopes). With their SD2 dual channel analyser instead (at an additional cost of 300 pounds), it would be possible to test for two radioisotopes at the same time. This equipment would enable one to get a very good idea of the radioisotopes present in food and environmental samples. This is probably the most expensive piece of equipment that any group should consider buying to check for radioactivity in food. For more complete analysis a university biology or radio biology department may be willing to analyse the samples. This equipment, like the other food monitors in this report, will not be able to detect alpha or beta emitting isotopes, unless separate detectors are purchased for these types of radiation, but it will be very good for detecting Caesium 137 and other beta/gamma emitters. COSTRONICS ELECTRONICS 13 Pield Heath Avenue, Hillingdon, Middx. UB8 3PB, ENGLAND. Phone 0895 38791. They have produced a gamma-sensitive, hand-held monitor called Mr Clean (terrible name). It has a meter calibrated in counts/minute and a GM tube, the ZP1220, mounted in a separate probe. There is also a pulse output which may be fed to a computer for integrating the count-rate over longer periods of time. The cost is 250 pounds. In addition, Costronics offer a scaler (150 pounds) and claim that either with this or with a computer, the Mr Clean would be useful for checking for contamination in food. However, the count-time needed for this purpose would be at least an hour. If used with either scaler or computer the device would be a suitable instrument for plotting changes in, or mapping the levels of, the background gamma count. COUTECH ASSOCIATES LTD Oxted Mill, Spring Lane, Oxted, Surrey, RH8 9PB, ENGLAND. Phone 0883 715216. Coutech make a cheap (89 pounds) gamma radiation monitor, the NRM-01, using the ZP1310 Geiger tube. This has a very simple operation, it records on a liquid crystal display the total number of counts detected since the instrument was switched on. It is left to the operator to time the count and calculate the dose rate. Although this could be an economical way of obtaining crude daily averages of the dose rate, the problems of calculating the dose rate allowing for internal background, etc, will probably be a drawback to any but the most dedicated of operators. Instruments that can do some of this work for you cost only a little more. They also make another version, the NRM-02, which uses the ZP1 320 Geiger tube and is therefore rather more sensitive. DR. VOGLER AUSTROSERVICE. Berg-am-Laim-Strasse 131a. D-8000 Munchen 80. Federal Republic of GERMANY. Telephone. 089 4316171/4312981. This German based company have recently introduced a static alarm monitor. It consists of a weather proof gamma sensitive probe which can be mounted on the outside of a building connected to a meter unit inside. The meter can operate either on mains power or batteries and has the capacity to drive various types of alarms, bells, lights etch and has an interface socket for connection to a computer. This unit costs 339 pounds, ex works but postage and customs fees will be in addition to this. EBERLINE INSTRUMENT COMPANY Unit 22 Southwater Industrial Estate, Station Road Southwater, West Sussex, RH13 7TW, ENGLAND. Phone 0403 732 150. This company imports a wide range of radiation monitoring equipment of which the following is only a selection. The Eberline Monitor 4 is a pocket sized, battery powered instrument with a built-in end-window GM tube. Although claimed to be sensitive to alpha, beta and gamma radiation it is not very sensitive to the first two and thus principally of use as a detector of gamma ray contamination, and even for this it is very energy dependent. It costs 155 pounds. It has both audible and visible indication, but the main readout is given on a meter calibrated in mR/hour. Eberline Smart Portable Model ESP-1 (price 650 pounds) provides, it is stated, " the functions of many instruments in one." It is a hand-held microcomputer controlled scaler/ratemeter which can be attached to a variety of different probes and reprogrammed to change its function. It is ultimately a matter of opinions but in the opinion of one of the present authors (Don Arnott) multipurpose instruments can be more trouble than they are worth; beginners in this field would be wise to stick to the rule 'one instrument - one function' (or at the most two !) Eberline also offer a cheaper, hand-held meter with audible warning as well as meter indication, the latter offered in several different calibrations, apparently to order. Price 480 pounds. Eberline also supply a food monitor, Type WAM4 but, at 9970 pounds including an ESP1, it cannot compete with British instruments. They also manufacture a series of hand-held probes. Of these the EIP-260 (190 pounds) is a high-sensitivity beta probe with a thin mica window; the HP190A (93 pounds) is similar but of lesser sensitivity. These could be useful for the measurement of surface contamination and could probably be made compatible with British instrumentation. Two different hand probes are offered for the measurement of gamma ray backgrounds these are the HP-270 (85 pounds) and the HP-290(155 pounds). Of these, the HP-270 is the more sensitive for low levels of gamma radiation. EUROPEAN ELECTRONIC INDUSTRIES LIMITED Station House, Station Approach, Birchington, Kent, CT7 9RF, ENGLAND. Phone 0843 46452 This is an electronics company which has recently started to produce simple cheap radiation monitors. The GC-1 is a pocket sized radiation meter (i.e. measuring radiation dosage) which also indicates radioactivity in counts/sec (see below). It also has audible warning and is battery operated. It can use either the (Mullard) ZP1310 GM tube, in which case it is sensitive only to relatively high levels of gamma radiation. Alternatively it may use the ZP1400 which has a thin mica window which will detect beta particles - but since the window of this tube is small compared to the tube volume, the beta sensitivity is low compared to the gamma sensitivity. The cost of this instrument is 69 pounds including VAT. The GC-2, cost 110.05 pounds, is the same except that the Geiger tube is mounted in a hand held wand on a 28 inch lead, which plugs into the meter unit. It is usually fitted with the same tubes as the GC-1, but Euro. Electron can fit alternative tubes at a slightly higher cost. For example they could fit the ZP1430 which will detect alpha and beta particles, or the ZP1220 giving higher sensitivity to gamma rays. The modified GC-2's would cost about 145 pounds ex.VAT. Some of the early GC-1 and GC-2 models have a scale calibrated in Becquerels; this is a mistake. It is not possible to read Becquerels directly off the scale of a simple hand held geiger counter. It should be calibrated in counts per second or per minute. They should be correcting this mistake on all future models. Fitted with suitable tubes these radiation monitors would be suitable for the detection of radiation contamination or the measurement of gamma dose rate. HUGHES CONSULTANCY. The Mount Laboratory, Toft, Cambridge, CB3 7RL, ENGLAND. Phone 0223 263122. Hughes are agents in the U.K. for: Amcor, Philips and Bicron. Vinten Instruments are also distributers for Bicron, so see their entry for details of Bicron equipment. Amcor make personal gamma and X ray monitors. They are pocket sized monitors which give an indication of the dose rate by giving audible bleeps. Their main application would be for staff working in environments in which they may need a warning of sudden increases in dose rate, such as X ray machines being accidentally switched on while they are in the vicinity. They do not give any numerical readout of the dose rate. They cost about 80 pounds each. Philips make the PW 4514/10 a pocket beta-gamma-X ray dosimeter costing 365 pounds. It has a liquid crystal display, an alarm feature and can display the dose rate and the accumulated dose. It is suitable for much the same applications as the Amcor monitors but gives more information about the dose rate because of its liquid crystal display. MAPLIN ELECTRONIC SUPPLIES. P.O. Box 3, Rayleigh, Essex, SS6 8LR. Maplin produce a do-it-yourself radiation monitor kit. The LM24B Geiger Counter Kit costs 99.95 pounds and includes all parts necessary for construction. The completed monitor is a portable light weight model. It has a meter for displaying dose rate with three ranges, up to 0.5 millirem per hour, up to 5 mR/hr. and up to 50 mR/hr. It has an audible indication of dose rate, a flashing L.E.D. to indicate events detected and a pulse output for connection to a computer. It runs either on a 9 volt battery inside the case or an external 7-14 volt power supply. It uses an AG1407 thin end window geiger tube for the detection of alpha, beta and gamma rays. This is mounted inside the instrument case. Another kit the 'LM25C Geiger Remote Kit' costing 79.95 pounds includes all parts necessary for the construction of a weather tight external geiger probe which can be connected to the LM24B as a remote detector. This can be attached by up to 100 meters of cable and uses the same geiger tube as the LM24B kit. These kits are rather more sophisticated than the Phonosonics kits and will require considerable skill with a soldering iron to complete them successfully. When completed the LM24B kit is similar in performance to the Eberline Monitor 4, and if competently put together, is in no way inferior in terms of robustness and finish. MINI-INSTRUMENTS LTD. 8 Station Industrial Estate, Burnharn on Crouch, Essex, CMO 8RN, ENGLAND. Phone 0621 783282 This firm offers a wide range of equipment, not all listed below, used mainly in laboratories and hospitals. Several of their products, including both contamination meters and radiation dosimeters, would be useful, and they are generally reliable and reasonably priced. All of their 900-series Mini Monitors have the following features in common, audible warning which can be preset to trip as required; battery operated with or without rechargeable cells; optionally mains operated (separate mains unit avail Abe both for this and for charging rechargeable cells); logarithmic meters which avoid the need for range-switching. The instruments are portable but bench-standing rather than hand-held and all the detectors are mounted in separate probes. Mini-monitor Type E costs 250 pounds and uses a thin end-window GM tube, the ZP 1430. It will detect both beta and alpha particles and is thus useful for the measurement of surface contamination. Type EL costs 258 pounds is similar to Type E but three times as sensitive. However, the tube is delicate and easily damaged, and Mini-Instruments do not recommend this model for the general public. These monitors are also available in three types for the measurement of radiation dosage. Of these the Type G is the one most suited to our purposes. Its logarithmic meter his calibrated over the range 0.05 - 75 microSv/h. Its cost is 270 pounds. Mini-Instruments also supply a variety of scintillation probes which may be used in conjunction with these monitors for specific purposes. The Type 44A scintillation probe (232 pounds, probe only) is useful for monitoring gamma-ray emitters; it is especially sensitive to low energy gammas and will also detect some high-energy beta-particles. Mini also offer three scalers, such as the Type 6-20. This is intended for radioactive assay and has a digital read-out and a versatile series of pre-selected time intervals (1, 10, 20, 50, 100, 200, 500 and 1 000 seconds) allowing great sensitivity. A similar instrument is also available, calibrated in microSv for radiation dose measurements. The cost of each is around 285 pounds. The Minalarm Type 7-10 is a fixed alarm monitor. It is available with a choice of three different sensitivities of gamma sensitive Geiger tubes. The 7-1OG version uses the same Geiger tube as their environmental monitor described below, and is therefore most suitable for low level radiation detection. This alarm monitor costs 386 pounds including the MC70 Geiger tube, and would be suitable for fixed alarm monitoring around nuclear installations. The first in a new range of Mini Instruments monitors is the Series 1000 Mini Rad. This is a portable gamma survey meter with an internal ZP1201 energy compensated geiger tube. It has a logarithmic scale and an alarm feature. It is smaller and more portable than previous Mini Monitors, with a showerproof case. The cost is 195 pounds. Finally Mini-Instruments offer three pieces of equipment of especial interest, as follows : Their ENVIRONMENTAL GAMMA RAY MONITOR TYPE 6/80 (price approx. 523 pounds) consists of a scaler/ratemeter and their compensated geiger tube, the type MC70. It will only detect gamma rays, and is very good for measuring the level of background gamma radiation. It is not very suitable for looking for low levels of radioactive contamination on the ground or in food. It is being used by a group called the Druridge Bay Baseline Study to produce a map of the background radiation in their area against which any future increases can be compared. It was also used by the British National Radiological Protection Board to prepare their gamma ray background radiation map of the UK and is also used in many other countries. Mini-Instruments now make a FOOD MONITOR, consisting of a scaler and a Type 41 S scintillation detector, with lead shielding; cost 735 pounds (excluding carriage and VAT). This is the cheapest instrument which we have yet found which is capable of detecting low level radiation in food. It only detects gamma rays, but it will detect the presence of isotopes such as Caesium 137 and Iodine 131 with a good level of accuracy. It will give a very good indication of the amount of radioactivity present in food samples, but it will not be able to determine what isotopes are present. For the identification of specific radioisotopes much more expensive equipment is necessary. It is supplied with a 100Bq/Kg standard to calibrate it, this consists of 55g of Potassium Chloride which is made up to one litre with water. It also is supplied with an instruction manual giving good advice on counting statistics. However it is essential to have information on the normal level of radiation present in food due to naturally occurring isotopes like Potassium 40 to be able to interpret the results at levels below 50Bqtkg or so. Mini-instruments also make a BEACH MONITOR (cost 490 pounds ex VAT) specifically designed to detect gamma and beta emitting isotopes on the ground. It has been used by the M.A.F.F. and is good for looking for levels of contamination on the ground without crawling along on your hands and knees. It has two glass walled Geiger tubes mounted on the end of a long handle and a meter unit with a carrying strap. It will not detect alpha emitting isotopes or low energy beta emitters. However the pollution found on beaches is likely to contain at least one high energy beta/gamma emitter to enable it to be detected. It could be useful for groups or local authorities who wish to survey their beaches, as it permits the rapid sweeping of an area for radioactive contamination fairly conveniently. NUCLEAR DATA INC.(UK). Nudata House, Wessex Road, Bourne End, Bucks, SL8 5DU, ENGLAND. Phone 06285 22733/4. Nuclear Data make a range of expensive microprocessor based spectrometer type equipment with prices for a complete system of about 20,000 to 30,000 pounds. This equipment will be able to determine exactly which gamma emitting radioisotopes are present in food or environmental samples, but some training in how to operate it and interpret the results would be necessary.It would work out very much cheaper, in the short term, to ask a university or medical school biology or radiobiology department to do this type of analysis; this could cost from about 10 to 50 pounds per sample. NUCLEAR ENTERPRISES LTD. Bath Road, Beenham, Reading RG7 5PR, ENGLAND. Phone 0734 712121. This firm manufactures a wide range of instruments of which this is only a selection. PCM5 Portable contamination Monitor: pricey but very good. It costs 717 pounds excluding the DP3 dual purposetprobe (which separately costs 503 pounds). This particular probe in conjunction with the PCM5 allows the separate or simultaneous assessment of alpha or energetic beta particle surface contamination, the light-tight detector window is exceptionally large, which gives added sensitivity. Contamination levels are indicated by meter-deflection with a logarithmic scale. It is normally battery-operated but there is an optional mains-power unit. A unique and valuable feature of this instrument's audible warning is that it has two tones; one for alpha and one for beta, which can be heard separately or in unison. A fine unit for those for whom price is not the main considerations but there are cheaper ways of obtaining approximately the same result. The DP3 cannot be married to other manufacturers' instruments without loss of its dual function, but Nuclear Enterprises make three scintillation probes which are more versatile in this respect. These are the BP4, BP6 and BP7. They are sensitive to alpha particles and both hard and soft beta particles. Of these the BP6 is the most sensitive. Nuclear Enterprises also make a scaler, the ST7 (1109 pounds) which, in addition to normal functions (digital read-out etc) has threshold and window controls which allows identification of particular radioisotopes by their gamma-ray energies. They also sell a Food Monitor (around 1906 pounds) which comprises this scaler and a DMI/2;8D8 sodium iodide scintillation probe and various plastic containers for food samples. This unit does not incorporate any lead shielding and, unless users provide their own, the measurement of low activity samples will be troublesome because of natural background count - thus leading to loss of sensitivity. This food monitor is not supplied with a test sample of known activity for calibration purposes, unlike the corresponding Mini-Instruments device. But it is not difficult to supply one's own. Moreover, unlike the Mini equivalent, the Nuclear Enterprises instrument is able to discriminate between different radioisotopes. [] TL: RADIATION MONITORING. An introduction. (GP) SO: Greenpeace UK DT: 1988 Keywords: nuclear power radiation weapons uk europe greenpeace groups gp / [part 4 of 5] PERSONAL MONITORING TECHNOLOGIES, INC. Metro Centre, 88 Elm Street, P.O. Box 40608, Rochester, NY 1-604-0008, U.S.A. This company are marketing personal gamma dose monitors, They consist of a credit card sized plastic card. This encloses a TLD based detector which must then be returned to them at yearly or six monthly intervals to be read. The cost per card is $19.50, which includes the cost of reading the card and giving you the result. A second version of the card includes three removable additional TLDs which can be used to monitor individual exposures to medical or dental X rays or any procedure involving radiation exposure. In a survey they conducted using these detectors 40 % of dental X rays were found to exceed the US government recommended maximum dose for this procedure of 350mR per exposure. These cards would be useful for monitoring one's cumulative gamma dose over the year and may be of particular interest to anyone concerned about exposure due to medical X rays or nuclear medicine procedures. PERSPECTIVE UK LTD. 111 Baker Street, London W1M 1LA, ENGLAND. Phone. 01 486 6837/8 or, 01 935 1470. This company have launched a new range of small portable gamma radiation monitors. There are three versions the Radalert 1310 (86 pounds), Radalert 1313 (129 pounds), and the Radalert 1201 (169 pounds). The number part of the name describes which Mullard Geiger tube the monitor uses. The Radalert 1201 uses the ZP1201 and so on, although some 1201 's use an American made equivalent of the ZP1201. The 1310 is designed for schools and educational use but it has such a low sensitivity that it is unlikely to be of use in this application. The 1313 has the same sensitivity but is energy compensated and is intended as a high dose rate monitor for civil defence or armed forces use. The 1201 has the most sensitive tube and is therefore the most useful. All models are microprocessor controlled, with three functions: function one displays a continuous instant calculation of the dose rate over a short (six second) time interval; the second is a setting which enables a count to be made over 1, 2, 5, or 15 minutes, for greater accuracy; and the third simply counts up the events detected and displays them along with the time in seconds since the count was started. In the case of the first two functions, the dose rate is automatically displayed in Sieverts, milliSieverts or microSieverts as appropriate. All three devices are pocket sized with an built in Geiger tube and a user settable alarm function. The company intend to introduce other more sensitive monitors in the future, including a Radon monitor. As yet Radon is difficult to detect directly without very expensive specially designed ionisation chambers. PHONOSONICS 8 Finucane Drive, Orpington, Kent, BR5 4ED, ENGLAND. Phone 0689 37821. A small firm, in the DIY electronic kit business and offering a range of monitors either ready-made or as kits. Their first two were introduced as constructional projects in electronics magazines. All the Phonosonics units are basically contamination-meters. The unit designed for Practical Electronics has audible warning, a count rate meter and a pulse output which may be fed to a computer for count analysis. The unit designed for Everyday Electronics is similar but omits the meter. A third unit is pocket sized and uses a light emitting diode which flashes with each count detected; its output can also be fed to a computer or a high impedance crystal ear piece. A fourth unit, is a ready-built monitor, the TZ 272 Sit has a counts-per-minute meter and a pulse output socket. All four units are battery operated and cost from 49.62 pounds to 89.32 pounds. These kits may have a use in enabling one to keep a check on the general level of gamma radiation. Should there be another Chernobyl type disaster, one of these kits may be able to give warning of the increased level of gamma radiation (if the levels reach at least ten times the levels recorded in the UK during May 1986). They would be of no use for checking for levels of radiation in food. Someone who has a good knowledge of electronics, such as from building other Practical Electronics kits may be able to improve them by fitting a better tube such as a thin end window ZP1430 or the gamma sensitive ZP1220. Different probes will require different voltages from the power supply in the meter, and they will require careful setting up in order not to damage them and to get the best use out of them. John Becker of Phonsonics should be able to advise you on which alternative probes could be used with his kits. The pulse output socket may enable one to integrate the count over longer periods of time, in the same way as a Scaler-Timer, giving greater accuracy. One of these kits modified with a more sensitive probe and connected to a cheap computer, may be able to check for low levels of radioactive contamination more cheaply than by buying more expensive ready-made equipment. RADIATRON COMPONENTS LTD. Crown Road, Twickenham, Middlesex, TW1 3ET, ENGLAND. Phone 01 891 6839. Radiatron are U.K.agents for G.S.T, Xetex and Rotem. G.S.T. make pocket sized pen shaped dosimeters, the Pendix range. They cost 239 pounds each. They give a liquid crystal readout in Micro Sieverts per hour. They are used for personal dose measurement in nuclear installations but will have little application for environmental monitoring. The Bleeper III Monitor is a similar device but with only an audible indication of dose rate by way of a series of bleeps. It costs 129 pounds. Xetex Inc of 660 National Avenue, Mountain View, CA 94043-2257, U.S.A. make a range of dose rate meters and contamination monitors. These include a wide range of dosimeters with prices from 160 pounds to 400 pounds, and rate meters from 350 pounds upwards. Rotem make the RAM-D radiation monitor which may be used with a variety of probes, it is a microprocessor controlled meter with a digital display. SAPHYMO-PHY. 18, rue de Villeneuve. Silic 551. 94643 RUNGIS CEDEX. FRANCE. Phone. (1) 46.87.25.16. This French company manufacture a range of monitoring equipment including personal dosimeters, contamination monitors, ionisation chambers and other equipment which is used by the nuclear industry in France. The SBN90 is a weather proof continuous gamma monitor. Designed for a fixed location it produces a continuous record of the dose rate on paper tape, with both a printed digital readout and a standard pen plot. It is capable of detecting transient peaks in the dose rate. It can contain a roll of paper tape long enough for one months continuous use. The detector used is a Sodium Iodide scintillation detector. This gives greater sensitivity to low level radiation than most Geiger tubes. It is designed for monitoring gamma levels around nuclear power stations, reprocessing plants etc. The SBN90 costs 89,450 Francs (8,900 pounds). Around 110 units are in use around France since 1980. SIEL IMAGING EQUIPMENT LTD. Orpheus House, Calleva Park, Aldermaston, Berkshire, RG7 4QW, ENGLAND. Phone 07356 71828. Siel supply two quite expensive American made survey meters: The Digital/Analog Survey Meter, cost 917 pounds. Has both digital and analog liquid crystal displays, calibrated in milliRem per hour. It is sensitive to alpha, beta and gamma radiation. It has a freeze function which enables it to store the highest reading it detects while this function is in operation. It uses an air ionisation chamber. The Panoramic Survey Meter cost 1,546 pounds also uses an ionisation chamber. It is slightly less sensitive to low energy beta rays and alpha rays than the digital/analog meter. It is designed to be directional, allowing one to more easily find sources of gamma radiation while surveying. It is calibrated in milliRem per hour. With both of these meters the dose rate indication will only be relevant to gamma radiation. They will also be very alpha and beta particles. VINTEN INSTRUMENTS LTD. Jessamy Road, Weybridge, Surrey, KT13 ALE, ENGLAND. Phone 0932 57711. Vinten are the U.K agents for Bicron Corporation 12345 Kinsman Road, Newbury, Ohio 44065, U.S.A. Bicron make an extensive range of survey equipment, including the Analyst Survey meters calibrated either in counts per second or units of dose rate. These cost between 750 and 1,115 pounds exclusive of probe, and can be used with a wide variety of Bicron probes. The Surveyor 50 is a portable survey meter costing 365 pounds; for an extra 80 pounds it can give an audible indication of count rate. This is calibrated in milliRem per hour or micro Sieverts per hour and can be used with Bicrons range of probes. Bicron Geiger Muller probes cost from 115 to 455 pounds and depending on type will detect alpha, beta or gamma radiation. Bicron can also supply Scintillation type probes costing from 400 to 3 ,000 pounds, and a bench mounted Scaler Ratemeter, the Labtech, costing 1,750 pounds. WALLAC (NEWBURY) LTD. Crown House, Kings Road West, Newbury, Berkshire, RG14 5BY, ENGLAND. Phone 0635 49429. Wallac are U.K. agents for: Alnor Oy, Ruissalontie 11, PL 506, 20101 Turku 10, Finland. Phone 358 21 308 700, and Herfurth GmBH, Beerenweg 6-8, d-2000 Hamburg 50, Postfach 500684, Germany. Phone Hamburg 213 623. Alnor make the following instruments: The RD-10 is a very rugged gamma radiation survey meter. It is designed to military specifications and may have applications for civil defence or fire brigade use, where exceptional toughness is required. It costs 719 pounds in the U.K. but may be a little more affordable in its native Finland. The RD-10B at 1,099 pounds is a version of the RD-10 incorporating an external end window geiger tube for the monitoring of beta and alpha contamination as well as the internal gamma tube as in the RD-10. Both have an illuminated LED display good for reading the dose rate in poor illumination. They are both calibrated in milliRem per hour. They also make the RAD 21L and RAD 22 which are pocket dosimeters, the 22 has an alarm feature as well, and they both cost 429 pounds in the U.K. Their purpose is to monitor the personal dose for radiation workers in the same way as film badges etc. Wallac also make a Neutron Detector, and a Thermoluminescent Dosimeter System. USE AND CARE OF EQUIPMENT In practice, radiation monitoring falls broadly under three headings: (a) Looking for radioactive contamination ; obviously useful, though usually no more than semi-quantitative. (b) measurements of gamma ray dose rate. (c) Exact sample measurement e.g. analysis of radioactive material in foodstuffs. This requires a laboratory and (usually) some sample preparation and is thus both more sophisticated and more time consuming than (a) and (b). In all three cases the measurements made must also include determination of the natural radiation background. One thing needs to be made clear at the outset because it applies to greater or less degrees to all monitoring systems and programmes. It is indeed possible for the absolute beginner to obtain results from any of them with no more than the manufacturer's instruction manual as guidance. In fact, it is not merely possible, it is all too easy. For it is a common and inherent defect of this sort of instrumentation, that when it is on the blink or improperly operated, it is liable to give spurious counts or other readings. Since there is no way of distinguishing these from genuine signals the result can be highly misleading or even alarming. These systems, are not, in general, "fail safe". It is therefore desirable and, for more sophisticated operations such as exact sample measurement, it is essential to obtain at least some instructions from somebody who has prior experience in this field. Since most of the instrumentation we have listed here has been around for years in one form or another, and is already in common use in places such as hospital and university laboratories, such help is not difficult to obtain. (a) CONTAMINATION MONITORING. This is essentially field work, and its objective is to locate areas of concern as speedily as possible. This can only be done by carrying out a relatively large number of measurements as rapidly as possible. The measurements therefore have to be as simple and as straightforward as possible. It does not matter that, for the most part, they will only be semi-quantitative - for their ultimate function is to direct attention to those areas in which exact determinations of radioactivity will be of greatest value. But these exact determinations are far more time-consuming, were one to use them to determine, say, the extent and passage of a fallout cloud from a nuclear reactor in trouble, the next unfortunate event might well be on its way before one had finished mapping the first. Some practical considerations will now be briefly listed. Field instruments which give audible warning of radiation by means of loudspeaker clicks are far more valuable than those which do not, whatever their additional means of recording data may be. The reason is that the human ear can instantaneously detect any increase or decrease of click-rate, which obviously enables one to identify areas of greatest concern far more rapidly than otherwise. This point has been made earlier ;it is important enough to bear repetition. Contamination of the detectors themselves (GM tubes or scintillation probes) is an ever present risk and may prove sufficiently permanent to ruin the instrument in the case of contaminants of long half-life. Since in practice what one is looking for will usually be gamma radiation it is often worth while to sacrifice an insignificant amount of detector- sensitivity by shielding the detector with polythene or Cling film. If one is looking for surface contamination arising from energetic beta-particles such protection is useful because the detector will be working close-in to the source of contamination. For the detection of alpha-particle and low energy beta particles even Cling film would be essentially self- defeating. In practice this does not matter because it is highly unlikely that any alpha or low energy beta particle measurements of any value would be obtainable under field conditions. This is because such particles are easily absorbed by even a thin film of dust, water, or indeed any other substance. It must also be borne in mind that all alpha and beta GM tubes are of the "end window" type and the windows are extremely fragile and, in particular, easily punctured. They are also highly directional i.e they receive their signals through the window only. Gamma-ray detectors, receiving radiation from all directions, do not have this property to any marked degree. But there is another way in which gamma-ray detectors are, in effect, partly directional. It is obvious that their maximum sensitivity will, especially in the case of lengthy GM tubes, lie along the side of the tube. They will also respond to what is called the Inverse Square Law. This states that the intensity of radiation travelling in straight lines (such as gamma rays) varies inversely with the square of the distance. In colloquial terms, this means that as your detector moves ever nearer to the source of the contamination, the count rate increases more than proportionately. All field contamination measurements will be liable to prove misleading, or even quite useless unless prior study has been made of the natural radiation background in the areas where the instruments are likely to be used. Some rocks are naturally radioactive, or preexisting levels of contamination may exist - though not part of the natural background radiation they too must be known about in advance. The first task which confronts the organisers of any monitoring scheme is thus to make detailed studies of the existing background levels. The normal performance of all field instruments used must be studied until one is thoroughly familiar with the responses obtained. Only then will it possible to determine with certainty when a radiation field has exceeded its usual level. (b) MEASUREMENT OF GAMMA DOSE RATE For this, at present the most important activity, the equipment involved is not basically different from that used in contamination monitoring; the difference lies in the units in which the equipment is calibrated, which are of radiation dosage in MicroSieverts rather than radioactive events in counts per second. The remarks previously made regarding precautions to be taken against contamination etc. also apply in general. For convenience the several ways in which the Gamma Dose Rate Ca.. be monitored may be divided into three headings; (i) Alarm or Continuous Monitoring (Using Static Monitors). (ii) Approximate Gamma Surveying (Using hand held Gamma Survey Meters). (iii) Accurate Gamma Monitoring (Such as Gamma Baseline Surveys) (Using a scaler to count the dose rate over many minutes). (i) Alarm or Continuous monitoring. Although an alarm feature may be fitted to some gamma survey meters or contamination monitors, there is a definite need for fixed static alarm monitors. These will usually consist of a weather proof gamma detector mounted on the outside of a building, or other secure location. This is attached by a cable to the body of the monitor mounted indoors. The monitor is set to trip and ring an alarm when the gamma dose rate exceeds a preset level. Some units will include a pen recorder or computer interface so that a continuous record of the gamma dose rate can be made. Alarm monitors enable one to automatically detect sudden increases in the dose rate due to accidental releases of radioactivity. They are used by government bodies around nuclear installations for this purpose. It may be a good idea for groups in the vicinity of such installations to install such monitors, although ideally a ring of monitors is necessary to take into account all possible wind directions. This type of monitor is able to monitor 24 hours a day 365 days a year, something no human operator could possibly do. Alarms of this type installed around a nuclear plant in Sweden gave the West its first warning that something had gone wrong at Chernobyl. These alarms are a basic first level of defence. They give no precise information on the nature of the problem, they simply give a warning that a more detailed investigation of the dose rate is necessary. (ii) Approximate Gamma Surveying This is done with hand held gamma detectors similar to those used for contamination monitoring. The main difference is that the instruments normally use an energy compensated gamma detecting Geiger tube, rather than the thin end window types used in contamination monitoring. This allows the instrument to be scaled in units of dose rate rather than in counts per second. The accuracy of these instruments is limited by the use of a meter which displays the dose rate based on the number of counts detected in the previous few seconds. Since this will, at low dose rates, be a small number the reading will fluctuate considerably about a mean value. When recording the reading obtained from such a meter some indication of the variation in reading should be given. This can be done by writing a plus or minus figure after the reading, based on observing the maximum and minimum readings between which the meter is fluctuating, to make it clear that it is not an exact reading. i.e .03uSv/h+-.02uSv The value of these dose rate meters is that they give a continuous reading and are able to give a rapid indication of changes in the dose rate over time or from place to place, ie. in the detection of hot spots. (iii) Accurate Gamma Monitoring. If a Geiger probe essentially the same as that used in a gamma survey meter is connected to a scaler in order to count the pulses over a preset time period (ie. 600 or 1000 seconds), then a reading of much greater accuracy can be obtained. This can be accurate enough to detect even small changes in the background dose rate from place to place or over time. One of the instruments which is widely used for this purpose is the Mini Instruments 6/80, although any suitable combination of geiger tube and scaler can be used if properly calibrated. Several monitoring groups have already purchased this type of equipment. Some information will now be given on the use and positioning of this type of instrument. This information is mainly relevant to baseline surveys and gamma ray mapping. For other monitoring purposes some of the rules may have to be ignored. For detailed information on how to calculate an accurate figure for the gamma dose rate using this type of equipment see Appendix 1. Appendix 2 lists some factors that can affect the reading you obtain. Most of the following has been adapted from information supplied by Peter Burgess of the British N.R.P.B. whom we thank for permission to reproduce it. Measurements should be made in compliance with the following criteria: 1) For 600 or 1000 seconds. 2) With the GM tube in a vertical position at one meter from the ground (Measured at the mid point of the tube). 3) After switching on the instrument allow at least 30 seconds for it to warm up. 4) If the tube is dropped or blown over the measurement should not be made for at least 30 minutes to allow the tube to restabilise. 5) The tube should be set up at least 30 meters away from 2 storey buildings, at least 50 meters for buildings over 2 stories. 6) At least 10 meters away from 1 meter high walls, 15 meters away from 2 meter walls. 7) At least 10 meters away from roads or other metalled surfaces. 8) Not in densely wooded areas. 9) Away from flooded or very wet land. 10) Away from rivers or large expanses of water. 11) Not for approximately 2 hours after thunderstorms occurring in periods of otherwise dry weather. 12) Over relatively even ground. The following data should be recorded: 1) serial number of instrument and detector tube used, 2) Operator's name. 3) Date and time of measurement. 4) Location of measurement (Grid reference or site number). 5) Total count and count period (ie. 600 or 1000 seconds etc.). 6) Type of land (meadow, ploughed field, etc). 7) Condition of land (Dry, wet etc) Care of Instrument. Instrument and tubes should be treated carefully. It is a good idea to protect the Geiger tube by covering it with a sleeve of 28mm diameter foam plastic pipe insulation. This greatly improves its chances of survival if knocked over (and has no effect on the reading as plastic foam does not absorb gamma rays significantly). After use, the instrument should be cleaned and dried before returning it to its travelling case. Some instruments are supplied with a bay of silica gel inside the instrument case. This is there in order to keep the electronics dry. Silica gel is supplied as granules. It is not soluble in water but is capable of absorbing large quantities of moisture and thus keeping instruments dry. When it is obviously no longer doing so it can be regenerated by heating on a hot stove for an hour, or to red heat for a shorter period. The absorbed water is driven off and the gel can be reused. Some gel includes a small amount of Cobalt Chloride, which gives it a blue tint when dry, and changes to a pink colour when the gel is saturated. Batteries should be replaced when the instrument gives a low battery indication. In some instruments this is shown by the whole display flashing. [] TL: RADIATION MONITORING. An introduction. (GP) SO: Greenpeace UK DT: 1988 Keywords: nuclear power radiation weapons uk europe greenpeace groups gp / [part 5 of 5] Check Readings. It is good policy to make some sort of check reading regularly, this is to check that the instruments performance and response to radiation is constant. We suggest that each user finds an area within a building away from windows etc, where the instrument is well shielded from gamma radiation due to isotopes which may be deposited on the ground outside (a cellar would be suitable). The instrument should always be set up in the same position in this area. If the instrument is used regularly then a monthly check that the 600 second count in this shielded area is the same, with allowance for statistical uncertainties, will confirm that the instrument's performance is stable. If the instrument is used infrequently a check reading should be performed each time it is brought into use. In addition to this routine test at least an annual check should be carried out. This, at minimum, should comprise a test in an area of known background (ie the same as for the routine check) together with a measurement at a known dose rate which is close to the instrument's maximum e.g. 50uGy/h. Calibration. It is very important that instruments used for accurate gamma measurements are properly calibrated. This involves checking the instruments against sources and instruments that are directly related to national standards. A calibration certificate is then supplied. In Britain, the CEGB Berkeley research labs are able to undertake this calibration service as is the British National Radiological Protection Board at its sites in Chilton, Leeds and Glasgow. The NRPB's fee for this service is 44 pounds per instrument. ABSOLUTE LIMITATION ON ACCURACY. The authors of "A guide to the Measurement of Environmental Gamma Dose Rate" state a figure for the smallest change in dose rate that can be regarded as significant. They estimate that changes in dose rate of less than 120uGy /year or 0.013 uGy /h in readings taken at one site over a period of one month should not be taken to be significant. To obtain measurements of greater accuracy than this much more sensitive equipment than a Geiger detector would be necessary. (c)EXACT SAMPLE MEASUREMENT. Contamination monitoring and dose rate measurement are essentially mobile, exact sample measurement is essentially static. The equipment is more sophisticated and expensive and careful sample preparation is often involved (milk and rainwater are exceptions) which in turn usually requires laboratory preparation. Background determinations are also more critical. In general, procedures are more demanding and time consuming. Our previous remark about obtaining proper training is once more emphasis Ed. Exact assays based on alpha-particles are only possible at this level, they remain extremely difficult and the interpretation of the results often obscure. This is because of the extreme ease with which alpha particles may be absorbed within the sample itself however exact its mode of preparation. Calibration of the instruments is extremely important; one must know their response, in terms of Becquerels, to all radioisotopes measured. For this purpose radioactive test- sources, exactly known as to isotopic composition and radioactive quantity, may be purchased from Amersham International. Additional information on how to work out the statistical error on food monitoring results and how to get the most accurate counting times may be found in the book "An Introduction to Radiation Protection", which is in the book list. For the most part the exact measurement of the isotopes present in food and environmental samples will probably be left to specialised laboratories, the expense of the equipment putting it out of the reach of most small monitoring groups. Whether the samples are to be analysed by one's own group or by a specialised laboratory, great care is necessary in the way the samples are prepared. Before sending away samples to be analysed by a laboratory please enquire first as to the mass of sample required, and the type of samples that they are able to test. Sending either too much or too little material, or something unsuitable for analysis may result in wasted time and disappointment. There follow some simple guidelines on the preparation of samples. We would like to thank Bernard Wilkins of the British N.R.P.B. in Chilton, for permission to reproduce this information. Bernard will be quite happy to answer any specific questions on sample preparation, if the following guidelines do not seem to apply. SAMPLING METHODS FOR ENVIRONMENTAL SPECIMENS. 1) Water. Drinking water should be placed directly into the sample container, but water from other sources should be filtered first and both the liquid and particulate sub-samples sent for analysis. The container should contain a small amount of concentrated nitric acid, typically 5ml for every one litre of sample. This is to prevent radionuclides in solution from adsorbing onto the walls of the container, plastic being the best container material. The date of sampling, the location, whether filtration or acidification has been carried out and the net volume of the sample should accompany the sample to the measurement laboratory. The purpose of the measurement should also be given. 2) Grass. Grass is generally sampled for two reasons: to estimate the subsequent transfer to milk and meat; to estimate the deposition of activity per unit area of ground. For transfer studies it is essential that the sample is taken from the area that the animals are grazing upon. For the estimation of deposition, the grass must be cut to within one centimeter of the ground over a specified area, normally one square meter. In both cases the fresh weight of the sample must be measured soon after collection. If there is to be a delay between collection and measurement, the grass must either be dried or stored in a deep freeze, but it must be emphasised that drying or cold storage may result in the loss of volatile elements such as Iodine. If deposition is to be estimated it is advisable also to take a soil core of known cross-sectional area to a depth of at least 10 cm from within the area of grass sampled. Ideally this core should be delivered intact to the measurement laboratory (see section 3). The date of sampling, the location, the area sampled, the fresh weight and the relevant data for any accompanying soil sample should be sent with the sample to the measurement laboratory together with the purpose of the measurement. Other animal foodstuffs such as silage or hay are important for evaluating transfer to meat and milk at certain times of the year. It is essential that the sample is taken from the fodder actually being consumed at the time. If there is to be a delay between collection and delivery to the measurement laboratory, the samples may either be kept in a deep freeze or, after the fresh weight has been recorded, dried and stored at room temperature. The date, location and fresh weight of the sample should accompany the sample to the measurement laboratory. Soil is sampled either to evaluate future transfer to plants, or as part of an estimation of deposition. Soil is best sampled with a purpose built corer, excavation with yard en tools being more laborious and less precise. The surface area and depth of the sample should be recorded. Ideally a core should be delivered intact to the measurement laboratory. If delivery is not immediate it must be kept cool and in a sealed bag so that it does not dry out. The date and location of the sample, its area and depth and the purpose of the measurement should accompany the sample to the measurement laboratory. 4) Vegetables and fruit. These are sampled in order to make estimates of dietary intake. Thus the edible portions must be measured separately. It is essential therefore that either the samples are prepared into edible and inedible fractions at the time of collection, or that they are delivered to the measurement laboratory in a suitably fresh state. The fresh weight of the edible fraction must be recorded. If there is to be a delay between collection and delivery the separated fractions should be dried or kept in a deep freeze. It is not possible to make meaningful measurements on decaying vegetation. Decay is generally accelerated when the sample has been washed. The date and place of collection, any separation of edible and inedible fractions, and any relevant fresh and dry weights must accompany the sample to the measurement laboratory. 5) Milk. A preservative should be added to milk samples at the time of collection. Sodium metabisulphite, about 0.5 gram per litre, is the most suitable. If there is a long delay between collection and delivery to the measurement laboratory, the milk should be stored in a refrigerator, not a freezer. It is preferable to sample from a bulk tank, either on an individual farm basis or, more commonly for the purposes oil dose evaluation, from the creamery. Sampling from individual animals is not recommended. The date and location of the sample, and the volume and specification of any added preservative must accompany the sample to the measurement laboratory. 6) Meat and Fish. Like fruit and vegetables, these are samples to provide an estimate of dietary intake, so that once again edible parts must be measured separately. For example fish should be gutted. Thus it may be necessary to separate the edible fraction at the time of sampling. If there is to be a delay between collection and delivery to the measurement laboratory, the sample should preferably be stored in a deep freeze. Alternatively, after the fresh weight has been measured, the sample can be dried and stored at room temperature, provided of course that the edible parts have already been separated. Decaying tissue will not provide a meaningful result. The date and location of sampling, the fresh and dry weights (if appropriate) and details of any preparatative steps should accompany the sample to the measurement laboratory. 7) Labelling and Documentation. If more than one sample is sent to the measurement laboratory, the outermost containment of each sample must carry a unique number that relates to the accompanying information. The name, address and telephone number of the sender must also be included. LOCAL AUTHORITY AND INDEPENDENT MONITORING GROUPS It may be that all of the equipment mentioned in this booklet seems to be out of reach, because its is too expensive. However there is a possible solution. Form a local monitoring group. Get together with some friends who are also concerned about radiation levels and pool your resources. If you can get a subscription of a few pounds each and organise some fund raising activities, even a 700 Pound food monitor should not be out of reach. It may also be possible to get donations from local environmental and peace groups. There are already many groups who have set up and purchased monitoring equipment. They are listed in the following section of this booklet. It may be worthwhile to contact these other groups for advice and information. One of these groups (Manhood Coastal Monitors) has applied for and been granted charitable status. This is a very good move, as it helps to make the group far more credible to local authorities and other official bodies. It helps to demonstrate to them that the group is performing a useful community service. There are many potential "spin off" benefits from forming a local monitoring group. The fact that people in your village or town will know that there is a local group actively monitoring radiation levels, will help to raise their awareness of this issue. It will help them realise that radiation is something that they should be concerned about, not something remote and separate from them. It will show them that radioactive contamination is a fact of life, and is with us all now whether we like it or not. It may also help to build up a sense of community, and show local people that there is something that they can do about apparently complicated issues such as radioactive contamination. It is very important however, to get expert advice. Contact scientists at local universities until you find someone sympathetic to your aims. Their radio biology, biological science or radiation protection departments should have the necessary expertise. They may also be able to run a detailed analysis on any suspect samples. They will probably charge for this, but if they are approached by a local non profit making organisation or charity, they will probably not charge more than 10 - 20 pounds per sample, for a gamma spectroscope analysis. This will be much cheaper than going out and buying 20,000 pounds worth of spectrometer for yourselves. Some of the laboratories which will be able to analyse samples for you are listed in the following section. Local and regional governments and authorities are becoming more interested in radiation monitoring and many are now in a position to check food and environmental samples. Ask them if they have the equipment and if they don't, ask them why not? When your group is set up, please contact Greenpeace Nuclear Campaign U.K. or Greenpeace International and we will be able to include your group in the following list when it is next updated. LIST OF INDEPENDENT RADIATION MONITORING GROUPS. GREAT BRITAIN. ARGOS Project. Contact: Graham Denman, 96 Berwick Road, Gateshead, Tyne and Wear, NE8 1RS. Phone, 091 478 6272. This group will be setting up a computer based gamma monitoring network in about a year, when development of the hardware is completed. This will consist of a central computer contactable by computer bulletin board, by anyone with access to a computer and modem. This will be linked to automatic remote monitoring stations which will telephone in their accumulated daily readings to the central computer overnight. Individual should cost in the region of 1000 pounds including probe, integral computer, modem and printer. Ayrshire Radiation Monitoring. Contact: Margaret Crankshaw 20 Rudloch Drive, Barrasie, Troon, Ayrshire. XA10 6UU. Phone, Troon 316008. This group have a Mini Instruments 6/80 and are undertaking regular monitoring at sites in their area. They have published results and are co-operating with the other groups in Scotland. Campaign for Nuclear Disarmament (CND). Contact: Patrick van de Bulk, 22 to 24 Underwood Street, London N1 7JG. Phone 01 250 4010. Patrick has a Radalert 1201 and has made measurements around nuclear power stations. Coastal Unit Monitoring Irradiation of the Environment. (C.U.R.I.E.) Contact: Anne Stringer, The Flat, The Old Vicarage, Yoxford, Saxmundham, Suffolk. IP17 3EP. Phone 0728 724432. This group intend to purchase equipment to monitor radiation levels around the Sizewell nuclear power station. They are also closely associated with the campaign against the PWR on the same site. Cowal Monitoring Group. Contact: Alastair Lewis (Secretary), Ryvoan, South Campbell Road, Innellan, Argyll PA23 7SL. or Dick Walsh ,Phone Innellan 383, or Linda Kirkwood, Phone Dunoon 5055. The Cowal group have used a borrowed Mini 6/80 to take gamma measurements in the area of the Holy Loch Submarine base. They have also had sediment samples analysed on a spectrometer. They are actively campaigning in their area about radioactive pollution from the U.S. submarine base. Druridge Bay Campaign. Contact: Rosmary Lumb, 32 Main Street, Falcon, Northumberland. or Bridget Gubbins, Phone, 0670 513513. This group are undertaking a baseline radiation study of their area which will produce a 'radiation map'. This will give them a baseline against which any future increases in radiation can be compared. They have the cooperation of Dr.J.Urquhart of Newcastle University in interpreting their results. They use a Mini Instruments 6/80 to make their measurements. They are also active in campaigning on the issue of PWRs. Friends of the Earth. Contact: Paul Daley, 26 to 28 Underwood Street, London N1 7JQ. Phone, 01 490 1555. Friends of the Earth Energy Campaign have a Harwell Caesium monitor and a Mr. Clean gamma monitor, they have conducted extensive sampling around Trawsfynydd. They are able to check samples for Caesium 134 and 137 on behalf of other independent groups. Highland Appeal for Radiation Monitoring. (H.A.R.M.) Contact: Hazel MacMillan, Bellevue House, Cromarty, Rossshire. IV11 1XJ. Phone. 03817 393. This group also have a Mini Instruments 6/80 and are conducting measurements over a wide area of Scotland. They also intend to purchase a beach monitor to survey the coastline, and shades for the monitoring of airborne radioactive particles. Manhood Coastal Monitors. Contact: Cecil H. French, 16 Warner Road, Selsey, Chichester, West Sussex. PO20 9DE. Phone. Selsey 4947. This group are undertaking monitoring of the beaches in their area with a Mini Instruments Type E contamination monitor. Manx Anti Nuclear Independent Action Committee. ( M.A.N.I.A.C.) Contact c/o Patrick Gribbin, 30 Stonleigh Street, London W11 4DU. Phone, 01 229 5286. Patrick has sent a series of environmental samples to the N.R.P.B. for analysis on behalf of this Isle of Man group. The samples were taken after Chernobyl and showed considerable contamination. Radiation Monitoring Group (Merionnydd). Contact: Pat Ward, 46 Branscome Farm estate, Barmouth. Phone, Barmouth 200 969, or Ian Russel (Information Officer) Phone, Llanbedr 376. This group have set up with the intention of monitoring radiation levels around Trawsfynydd. They have purchased a Mini Instruments 6/80, and may also get a single channel analyser for food and environmental samples. They intend to start monitoring in April 1988. Radioactive Pollution Survey Group Wigtownshire. (R.P.S.W.) Contact: Mr. Alan Richards, Dhuloch Schoolhouse, Ervie, Kircolm, Near Stranraer, Wigtownshire. Phone, 0776 854 246. This group do not have monitoring equipment of their own but have sent samples of silt from the local estuary for analysis and published the findings. They have also undertaken surveys into the incidence of cancer and leukaemia in their area, and mounted a travelling exhibition on nuclear issues. RADS Radiation Services. Contacts John Hopkins, BCM/RADS London WC1 3XX. Phone, 01 405 2767. This group are involved in the sale and hire of Mr Clean Geiger Counters. They have also undertaken gamma surveys around some nuclear power plants in Britain (Hinkley Point and Trawsfynydd). They can also retail the book: "An Introduction To Radiation Protection" (see booklist). University of Wales at Cardiff, Environmental Action Group. Contact Jeremy Griffith, 2 Cleppa Park Research Station, Coed Kernew, Newport, Gwent, NP1 9BU. Phone, 0633 680735. They have a Costronics Mr. Clean and have undertaken a baseline survey. Welsh Anti Nuclear Alliance. (W.A.N.A.) Contact Hugh Richards, PO Box 1, Llandrindod Wells, Powys, LD1 SAA. Phone, 09824 362. WANA have a Nuclear Enterprises PCM5 with the dual purpose alpha/beta probe and have used this to conduct various surveys and have also lent it to other groups. BRITISH LABORATORIES UNDERTAKING SAMPLE ANALYSIS. Edinburgh Radiation Consultants. 18 Cumin Place, Edinburgh EH9 2JX. Phone, 031 667 2430. Dr. R.F. Wheaton. Have analysed samples for the Wigtownshire Group and Friends of the Earth on their Gamma Spectrometer. St. Bartholomews Hospital Medical College. Radio biology Department. Charter house Square, London EC1. Phone, 01 251 1184. Dr. Barry Lambert. Have full facilities for Gamma and Alpha spectrometry. May analyse samples at a concessionary rate for independent groups. Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ. Dr. D. Stewart and Dr. G. Wyllie. Have a Germanium Lithium Gamma Spectrometer which is mainly used for teaching purposes, however they responded to our survey so it may be worth approaching them. Manchester City Council, Environmental Health Department, Town Hall, Manchester, M60 2JB, Phone, 061 234 4880. Dr. Martin Court is. They have a Gamma Spectrometer and a mini 6/80, and are willing to analyse samples for independent groups. Dr. Court is also coordinating the results obtained by local councils for the Institute of Environmental Health Officers. LOCAL AUTHORITY MONITORING. BRITAIN. The Institute of Environmental Health Officers (I.E.H.O.) are coordinating the efforts of the local councils, Nuclear Free Zones and others, who wish to set up monitoring programmes since the Chernobyl accident. It will usually be the council's Environmental Health Departments who will be responsible for this monitoring. There is as yet no comprehensive list of all of the authorities undertaking radiation monitoring, and the type of monitoring they will be conducting. The I.E.H.O. will be producing the final version of their report on local authority monitoring in the first part of 1988. A full list o, monitoring authorities should be available at about the same time. For the time being we will list those councils that we know are undertaking monitoring, although the final list will, we hope, be much longer. Borough of Barrow in Furness, Environmental Health Department, 47-49 Hartington Street, Barrow in Furness. They use a N.E. BP3/4A probe and a ST7 scaler to make measurements of surface contamination. Gross beta counts of samples are also undertaken using the above equipment in a lead shield (lead Castle) to reduce the background count. Gross alpha counts are also undertaken using a windowless DM1/2 scintillation probe and scaler. They will also be getting a Mini 6/80 and the Mini Instruments food monitor in the near future. Borough of Cleveland Pollution Control Group, Principal Environmental Health Officer, Stockton on Tees Borough Council. They have a Gamma counting facility and do regular counts of air filters and shades to determine airborne activity. They also have a Mini 6/80 for gamma measurements. City of Stoke on Trent, Mr. B. Ward Director of Housing and Health. PO Box 208, Unity House, Hanley, Stoke on Trent, ST1 4QN. Phone, 0782 744241. They are getting a Mini 6/80 and a Mini Food monitor. They will use these to monitor gamma levels at 6 sites in the city and to monitor the activity in food samples and rainwater. Lancaster City Council, Environmental Health Department, Town Hall, Lancaster. Mr. Gilbert Shaw. This Council are undertaking a comprehensive monitoring programme which is run by an outside consultant, Radman Associates. London Borough Of Haringey, Environment Support Unit, Civic Centre, High Road, Wood Green, London N22 4LE. Contact, Mike Melina. Mike has a Costronics Mr. Clean connected to an IBM computer, and has made gamma ray dose rate measurements. Manchester City Council, Environmental Health Department, Town Hall, Manchester, M60 2JB, Phone, 061 234 4880. Dr. Martin Courtis. They have a Gamma Spectrometer and a Mini 6/80, and are willing to analyse samples for independent groups. Dr. Court is also coordinating the results obtained by local councils for the I.E.H.O. Nottingham City Council, The Guildhall, Nottingham NG1. Contact Mr. Bonham. They have a Mini 6/80 and T.L.Ds for gamma measurements, and analyse food and air samples via an outside consultant. Nuneaton and Bedworth Borough Councils, Environmental Health Department, Council House, Chappel Street, Nuneaton CV11 5AA. Monitoring due to start soon. Have a Mini 6/80 and will use an outside consultant for sample analysis. Powys County Council, Radiation Monitoring Scheme. Emergency Planning Officer, Powys County Hall, Llandrindod, Powys, Wales. Gamma dose rate measurements undertaken with Mini Instruments Type G monitors, and also Mini 6/80's. Strathkelvin District Council, Director of W.Environmental Services, PO Box 4, Tom Johnston House, Civic Way, Kirkintilloch, Glasgow G66 4TJ. Phone, 041 776 7171. Monitoring at 6 sites using a Mini 6/80. May also set up facilities in conjunction with other councils to analyse food and other samples. MONITORING GROUPS AND LABORATORIES OUTSIDE OF BRITAIN. (Omitted .. unscannable) APPENDICES AND TABLES. (Omitted .. unscannable) EQUIPMENT COMPARISON CHART (Omitted .. unscannable) RADIATION UNITS SUMMARY. ACTIVITY (BECQUERELS) = number of radioactive disintegrations per second. ABSORBED DOSE (GRAYS) = energy imparted to unit mass of tissue. DOSE EQUIVALENT (SIEVERTS) = absorbed dose weighted account the harmfulness of different radiations. COMMITTED DOSE EQUIVALENT (SIEVERTS) = the dose equivalent delivered to the body in the 50 years following the ingestion of a particular quantity of radioisotope. EFFECTIVE DOSE EQUIVALENT (SIEVERTS) = the dose equivalent weighted to take into account the sensitivity of different tissues to radiation damage. COLLECTIVE DOSE EQUIVALENT (MAN SIEVERT) = the total dose equivalent delivered to a particular population due to a particular source of radiation. RADIATION UNITS- TABLES (Omitted .. unscannable) LIST OF RADIONUCLIDES (Omitted .. unscannable) KEY TO MONITORING PROCEDURES (Omitted .. unscannable) BOOKLIST Working Party on Environmental Radiation monitoring. Interim report. This is essential reading for any group interested in radiation monitoring. It is prepared for Environ Mental Health Officers but contains much information of use to others. It is the most relevant work on the subject we have yet found, and is strongly recommended. It may be obtained by sending a cheque for 2.50 pounds to: The Institute of Environmental Health Officers, Chadwick House, Rushworth Street, LONDON, SE1 OQT. (A final version of this report will be available in early 1988 and will contain much additional material of interest to independent monitoring groups.) An Introduction to Radiation Protection. Alan Martin and Samuel A Harbison. Science Paperbacks. Publishers; Chapman and Hall, 11 New Fetter Lane. LONDON EC4P 4EE. This is an ideal first book to read on radiation protection; it is a City and Guilds text book in which everything is explained step by step with examples and revision questions. It contains some useful information on how to calculate the statistical error in the readings from food monitors and scalers and is also recommended. Living with Radiation. National Radiological Protection Board Publishers: H.M.S.O. Price 1.50 pounds. This very useful illustrated booklet is produced by the N.R.P.B. and is thus rather establishment biased; however it is a very good introduction to radiation and dose limits. Radiation Risks - An Evaluation. David Sumner. Price 3.95 pounds. Publishers; Tarragon Press, Glasgow. ISBN 1 870781 00 7. This is a well written introduction to radiation and risk assessment. The author carefully explains most of the concepts that can be so baffling in the field of radiation risks. It is set out in a clear and readable style and is strongly recommended. He tries not to be pro or anti nuclear, but simply presents the information to help the reader to understand the concepts involved and decide for themselves. The author has published the book himself and is a qualified medical physicist. A Guide to the Measurement of Environmental Gamma Ray Dose Rate. F.W. Spiers, J.A.B. Gibson, I.M.G. Thompson. Price 6.50 pounds. publishers; National Physical Laboratory, Teddington, Middlesex, TW11 OLW. Phone, 01 977 3222. This book is essential reading for all groups conducting gamma baseline surveys, or other systematic gamma dose rate measurements. It covers the topic in great detail. Some of the information in this booklet is summarised from this publication. The wealth of detail and scientific information could be intimidating, but if one does not yet put off by this the text is in fact quite easy to read and understand. It explains the nature and variability of natural radiation, the characteristics of individual measuring instruments, choice of instruments and the inter-relation of measurements. It is strongly recommended. Introduction to Health Physics. Herman Cember. Price 25 pounds. Publisher; Pergamon Press. ISEN 0 08 030936 4. This weighty tome (500+ pages) is a useful reference work. The profusion of diagrams and equations make it totally impenetrable to the casual reader. It is really a degree level textbook. It contains much useful reference material on physics, nuclear structure, radioactivity, radiation measurement and radiation protection. It is not an easy read, however we have found it to be a good book to look things up in. It explains something of the statistics involved in radiation measurements and gives much other useful information. It would be good for radiation monitoring groups to buy collectively, as a reference book. Nuclear Power, Man and the Environment. R.J Pentreath. Price, 6 pounds. Publishers: Taylor and Francis Ltd. 4, John Street. London WC1 2ET. Tel, 01 405 2237. This is a detailed and technical treatment of the subject of radiation in the environment. It is written by a scientist employed by the M.A.F.F. and so tends to be rather uncritical of government policy. It does not mention Geiger counters at all, but does go into the subject of government monitoring of environmental radioactivity in detail. It is not as good a first book on the subject as some of those above. As with the Herman Cember book, many readers would find the technical details intimidating.