Man-made Radioactivity

61

CHAPTER 4

Man-made Radioactivity

4.1 I N T R O D U C T I O N The experiment of initiating nuclear transformation artificially was first carried out by Rutherford in 19 19. It was shown that when a particle emitted from 214po w a s absorbed on striking a nitrogen atom, oxygen and proton were produced by the following reaction: J4N((x,p)JTo

or

14N + 4He --~ 170 + JH

(4.1)

All nuclides obtained by Rutherford were the stable nuclides. In 1934 J. Curie first succeeded in artificially producing phosphorus-30 by bombarding aluminium with c~-particles. This was the reaction: 27Al(~,n)3~

or

27A1+ 4He .___)30p + 1n

(4.2)

This was the first man-made radionuclide. From that time on many species of radionuclides were produced by bombardment of elements with charged particles using the various types of accelerators. In addition, practical use of fission energy allowed production of a great amount of artificial radionuclides, not only by neutron irradiation generated with nuclear reactors, but also by processing spent fuel. Nuclear reactions are usually represented as eqs. (4.1) and (4.2), that is, on the left is the symbol for the target nuclides, the first symbol in the parenthesis indicates the bombarding particle (or projectile), the second the emitted particles, and the symbol of the product on the right. In the equation, the left side of the comma shows the system of the reactants, and the right the system of the products. Before and after the nuclear reaction, both the sum of mass number and the sum of atomic number remain unchanged. When a target, as a thin film, is exposed to a bombarding particle (projectile) at the flux [cm 2 s-~] or ~ for t s, the number of the target nuclide, N, decreases by the equation of

Chapter 4

62

dN dt

= - NOr

N = Noe-"*'

(4.3)

where o is the quantity defined by the nuclear reaction in question and the energy of the bombarding particle, and is called cross section which has the dimension of cm 2. Hence, N Ois N at t = 0. When the disintegration constant of the nuclide produced is s-1, the rate of production of the nuclides is expressed as eq. (4.4): dN dt

= -Nor

)vn = N 0 o C e - * ' - n

(4.4)

Solving eq. (4.4) for n, N 0o_______0~ -z, n = )~ _ or [e-"*' - e ]

(4.5)

If )v >> o~) and Ct -- 0, the radioactivity produced, n, is given by eq. (4.5), which is important in practical use. n = No, ( 1 - e -~')

(4.6)

Nuclear fission is the phenomenon that occurs when a heavy nucleus splits into two or more intermediate heavy nuclei. In the field of radiochemistry, the fissions of 233U,235U, 239pu, induced by neutrons, are often treated, and especially that of 235U by thermal neutrons is studied the most. The fission cross sections of several nuclides for thermal neutrons are shown in Table 4.1.

Table 4.1 Fission cross sections for thermal neutron Isotope

o[b] [1 b = 10-24 cm 2]

23eTh 233U 235U 237Np 239pu 24~ 241pu 241Am 242mAm

3.9x 10-5 531.1 583.54 1.9• -2 742.5 3.0x 10-2 1009 3.15 6600

63

Man-made Radioactivity

10'

I

~

10

~

1

1

9

1

I

Neutrons ~ ~ , of 14 MeV

_

Thermal neutrons Z

]0 ~

10~

/ .-.-~ 1 70 80

10 ~

I

90

i

t

!

I

1

100 110 120 130 140 150 MASS NUMBER

Fig. 4.1. Mass number-fission yield curves for the fission of 2-'Uinduced by thermal neutrons and neutrons of 14 MeV. Even after emitting neutrons, all the fission recoils still have too many neutrons compared with the protons, and have a trend toward more stable nuclei by repeating [3disintegration. The series connected with 13-disintegration is called a fission chain. The final member in the series is a stable nucleus without fail. As an illustration, the fission yield for 235U is shown in Fig. 4.1 the fission yield curve for 235U induced by thermal neutrons has a deep valley at the centre compared with that by the 14 MeV neutrons. Since two fragments are produced for one fission, the sum of the yields fragments amounts to 200%. In nuclear reactions, the total momentum of the system is conserved before and after a nuclear reaction, and the product nuclide should generally gain some kinetic energy of recoiling at the emission of ),-ray or a particle. When the energy of incident or the ejected particles is more than 10 KeV, the target atom may gain the recoiling energy exceeding the chemical bond energy (several eV) and consequently the product nuclide is knocked out of the molecule. An atom possessing such a high recoiling energy is called a "hot atom" and the field concerned with this kind of chemical change accompanying nuclear reactions is called "recoil chemistry" or "hot-atom chemistry". The recoil phenomenon is often seen with (n,),) reactions which are known in terms of the Szilard-Chalmers reaction (1934). Although the capture of a thermal neutron

64

Chapter 4

does not provide enough energy to break a chemical bond, the emission of 7 ray following the neutron capture may cause recoiling. The recoiling energy E gained by a target atom with atomic mass M (in amu) is given as: e(eV) =

537E~/M

(4.7)

where Ey (MeV) is the energy of the y ray emitted. For instance 128Iproduced by a (n,7) reaction on ethyl iodide is recoiled and hence, when shaken with water, it is transferred into the water phase in carrier free state (ideally speaking). This is the first example of Szilard-Chalmers reactions which are now extensively studied and used for the production of some isotopes in high specific activity. There are some special methods of chemical synthesis recoiling phenomenon (recoil synthesis). For example anthracene labelled with ~4C is synthesised by irradiating acridine with neutrons through Z4N(n,p)J4C reaction. Similarly 3H labelling is realised with the use of 3He(n,p)3H or 6Li(n,o03H. For this purpose the compound to be labelled is mixed with 4He gas or Li2CO 3 and then irradiated with neutrons. The recoiling phenomenon is, of course, also seen in decay processes. The occurrence of this phenomenon with c~ decay has been well known since the early days and employed as a separation process. It also takes place with 13- decay, providing various nuclear chemical substances. 52

5225MnO s- ~

__

24CrO 4

(4.8)

The spallation reaction is another example of special nuclear reactions, by which many nuclides' relatively small mass number (about 10 to 20, the smaller the number, the higher the yield) in comparison with the target nuclide is produced simultaneously. The example is: 37CI( p, 6 p4 n) 2s 17 12Mg

(4.9)

The actinide elements are the elements with atomic numbers of 90 till 103 being members of a transition series, the first member of which is actinium (Z = 89); fourteen electrons are added successively, beginning formally with thorium (Z = 90) and ending with lawrencium (Z = 103). The straightforward way to obtain light actinides is by neutron irradiation of elements of lower atomic number. For example the production of Pa has been produced by the transmutation of Th with neutron produced in a high-flux nuclear reactor.

23~

_.._)231pa+

(4.10)

The elements Am and Cm also exist in spent fuel. However, large scale production is performed by neutron irradiation of 239pu.

Man-made Radioactivi~

65

The synthesis of transfermium elements beyond Fm is succeeded by nuclear reactions of charged particles with targets of an actinide element of a lower atomic number. 239pu(~,n)242Cm ' 241Am(~,2n)243Bk ' 238U(12C,5n)245Cf

(4.11)

The physical and chemical characteristics of actinides are as follows: 9 In an aqueous solution of pH < 3, four structural types of actinide cations exist, these are M 3§ M 4+, MO + and MO 2+ corresponding respectively to M(III), 2, 2 M(IV), M(V), and M(VI). ~ At a low [H § concentration, actinide ions tend to undergo hydrolysis. For example, uranium (IV) begins to undergo hydrolysis in aqueous solution above pH > 2.9. As the pH increases, U(IV) eventually precipitates as hydroxide, U(OH) 4. The actinide ions of the (IV) state are particularly prone to hydrolysis and polymerisation. 9 Actinide cations have a strong tendency to react with various inorganic and organic ions or agents, forming complex ions.

4.2 I S O T O P E S IN E V E R Y D A Y L I F E

Isotopes of chemical elements represent a tool which can do certain jobs more easily, quickly, simply, and cheaply than competitive methods. Some measurements could not be done at all without the use of isotopes as there are no alternative methods available. Isotopes are ideal tools for use in analysis; a single atom can be detected when using radioactive isotopes, as compared to chemical methods in which the detection limit of an element is enhanced a million times. Stable isotopes can also be detected with great accuracy nowadays; although not quite with the same sensitivity as radiation-emitting isotopes. Most important, especially in biological and medical work, is that radioisotopes can be located during a biological process. The functioning of certain glands can also be checked, by first administering a small amount of a radioisotope and then following the path of this compound in the body simply by measuring the radiation from the outside. For people who may worry about these small amounts of radioactivity, it should be remembered that everyone constantly eats potassium in their food, which is in itself slightly radioactive, and with which animals and humans have lived for a long time. For most of these applications--and there are many--there is no alternative method. Larger sources, which emit penetrating radiation, can be used as a portable X-ray unit to check welds in underground pipelines. Such sources are also used for certain analyses especially suited for work in the field, such as in geology. Very large sources, some 1000 million times stronger than the activities used as tracers, can destroy bacteria or other spoilage organisms in food, can be used for sterilisation of medical sutures or syringes, or can impart specific desirable properties to some materials.

66

Chapter 4

As isotope sources are relatively cheap, the instrumentation is readily available, and the application simple, they find wide application in practically all fields of science and industry. It is not surprising that the importance of the use of these tools, in spite of the growth of other new methods, is steadily increasing.

4.2.1 Food and agriculture In agricultural research and application, isotopes and radiation play a part in so many fields and in so many ways that it is difficult to obtain a proper picture of their enormous importance. In laboratories isotopes are used routinely with an ever-increasing assortment of modern research aids. In emerging biotechnologies, which are used increasingly by scientists, isotopes are a basic tool without which research in molecular biology could not be done. The main agricultural problems that isotopes and radiation are helping to solve are: 9 determination of conditions necessary for optimising fertiliser use and its efficiency for biological nitrogen fixation; 9 breeding of high performance, well adapted and disease resistant agricultural and horticultural crop varieties using radiation induced mutations; 9 eradication or control of insect pests using insects that have been radiation sterilised or genetically altered; 9 improvement of reproduction performance, nutritional status, and health of animals using radioimmunoassay and related techniques, as well as isotopic tracers; 9 reduction of post-harvest losses by suppressing sprouting and contamination using radiation treatment; 9 reduction of food-borne diseases and extension of shelf-life using radiation; and 9 study of the ways to reduce pollution from pesticides and agrochemicals. A good crop needs soil with adequate amounts of nutrients and moisture. Nuclear techniques are ideal tools for measuring the efficiency of fertiliser use by crops and for keeping a watch on the moisture content. In modern agriculture, the use of fertilisers is essential to maximise crop yields; for example, a 50% increase in grain yield of cereals is common in many soils through efficient fertilisation. In order to provide food for the constantly increasing world population, the projected fertiliser consumption in 20 years' time is estimated to be 4-5 times greater than today' s. To reduce the fertiliser requirement to an absolute minimum and thereby save production costs to the farmer and reduce damage to the environment, studies to obtain information on the relative merits of different fertilisation practices--such as methods of fertiliser placement, times of application, and types of fertilisersmare needed. The method used to solve these problems requires the introduction of known quantities of fertiliser labelled with isotopes to the soil at various times and in different positions. Since the plant does not discriminate between elements from the labelled fertiliser and those from native soil, the exact amount of fertiliser nutrients taken up by the plant can be measured.

M a n - m a d e Radioactivit 3,

67

The results of this type of research have been incorporated into agricultural practices for cereals and have increased crop productivity significantly, reduced fertiliser use--and thereby costs--and helped the environment by markedly reducing residual fertiliser in soils. Recommendations based on the results of experiments in this area have been adopted in FAO-organised fertiliser programmes in many countries and great savings have been reported; one country using these techniques claims to have saved as much as US $36 million per year on maize crops alone. Similar natural methods have been adapted to evaluate deposits of cheap rock phosphates as an alternative to expensive, often imported, phosphate fertilisers, and to find the most efficient way to use these fertiliser deposits for maximum plant growth. Although nitrogen constitutes 80% of gases in the atmosphere, few plants can directly make use of it. However, through fixation, plants are able to use the nitrogen in the air. The most important results are obtained from a symbiosis between a plant and a bacterium, which has gained great attention during recent years. Legumes that fix nitrogen can provide high protein for human and animal consumption and also increase nitrogen in soils. The water plant Azolla, for example, can drive 80-90% of its nitrogen by fixation, and is valuable in providing nitrogen to paddy rice crops. In order to obtain maximum benefits from this unique biological process, isotopes and used to find the amount of nitrogen that a plant can fix and how this process can be improved. Isotope techniques are an ideal tool to distinguish nitrogen derived from the atmosphere, soil, and applied fertiliser. Water is the most important limiting factor for crop production in many areas of the world. The efficient use of water in irrigation systems requires continuous monitoring of the moisture content of soil. Neutron moisture gauges are ideal instruments for this purpose and help soil physicists to make the best use of limited water resources. Through these methods, traditional irrigation methods are improved and in some cases up to 40% of the water can be saved. Agricultural production relies heavily on chemical inputs" fertilisers to boost production and pesticides to suppress weeds and control insects. Excessive use of these chemicals harms the environment as well as the food products. Isotopes are ideal tools for studying the behaviour, breakdown, and residues of agrochemicals in soil, water, plants, animals and their products. As a result of their use, it has been possible to devise safer ways to apply agrochemicals and safer formulations which are more effective in controlling pests or promoting growth, as well as being less harmful to health and the environment. For centuries, mankind tried every possible way to improve quantity and quality of crops. Natural evolution results from spontaneous mutation and selection of the fittest mutants. The rate of mutation occurrence can be multiplied by radiation treatment thereby accelerating evolution and the selection of superior crops. Over the last 50 years, a number of plant breeding programmes have included mutation induction with radiation or chemicals to breed improved crops. Physical mutagens like X-rays, gamma rays or fast neutrons are most frequently applied and their use has resulted in the highest number of improved, mutant crops. The

68

Chapter 4

Table 4.2 Economically important mutant varieties (source: IAEA) Crop

Variety

Country

Barley

Trumpf, Triumph Diamant, Krystal Midas Gratiot, Sanilac Arun NIAB78 Lumian No. 1 Star Rugby Wasata, Heiga, Jaran Stellar Calroise 76, M-401 Kashmir Basmati IRAT 13 RD 6 Atomita II Yuanfengzao Ahnsanffae Kalika CO 449, Co 997 Pervenets Casterporziano, Creso Cargidurox, Novosibirskays 67 Sirius Mv 8

Germany, UK CSFR UK USA India Pakistan China USA Poland Canada USA Pakistan Ivory Coast Thailand Indonesia China Korea India India USSR Italy France USSR Germany Hungary

Beans Castor bean Cotton Grapefruit Pea Rapeseed Rice

Sesame Sugar cane Sunflower

number of induced mutant derived crop varieties now exceeds 1500 worldwide with billions of dollars added to farmers' incomes annually. Some of the economically important mutant varieties are shown in Table 4.2. Important desirable properties which can be achieved by radiation include: 9 I m p r o v e d lodging resistance: the desired properties are a reduction in plant height and a stiffer stem, which can withstand rain and storm. 9 C h a n g e d maturing times: early maturing is important to escape frost, pests, etc., or simply to make room in the field for other crops. 9 I n c r e a s e d disease resistance: becoming very important in attempts to decrease the use of chemicals which are used against pests to protect the environment. 9 I n c r e a s e d yields: the yield of many crop varieties has been increased manifold after mutation breeding using nuclear techniques. ~ I m p r o v e d agronomic characters: for example, more winter hardiness, greater tolerance against heat, or generally better adaptability to available soil conditions.

Man-made RadioactiviO,

69

9 I m p r o v e d seed characteristics: improvement of nutritional value (protein or oil

content), baking and melting qualities, or reduction in cooking time. Many of the radiation induced mutants have made a great impact on the income of the region where they took place, in some cases even on the national income. One of the earliest successes concerns peppermint. The only source of peppermint oil in the United States was the Mitcham variety which succumbed to a fungus disease. Crossbreeding methods failed to produce disease-resistant peppermint. Radiation techniques led to induction of resistance which saved the original peppermint taste enjoyed by millions all over the world. Another remarkable success story of applying radiation to obtain economically significant mutants was achieved in Pakistan. There, a new cotton mutant was released by the Pakistan Atomic Energy Commission in 1983. It turned out to be the most productive variety in the country. The cotton production in Pakistan was roughly doubled! It is estimated that the crop value of this mutant during 1988-1989 was more than US $1600 million. However, not always does the success of a mutant show so quickly as in this case; sometimes it takes more than a decade before the usefulness of a new mutant is fully recognised (source: IAEA). In Italy, where nearly everyone eats pasta, 50% of pasta stems from a wheat variety developed through mutation. In China extraordinary results were achieved with this method: a certain type of rice now matures 24 days earlier, another type has a 20 cm shorter culm and in a third mutant a very high protein content was achieved (15.6%). Virtually hundreds, if not thousands, of such benefits have been developed over the last 10 years by artificially produced mutation in China alone where almost a tenth of the total crop acreage is under mutant-derived crops. The list of countries which have released crop varieties developed through induced mutations is impressive. There are more than 40 countries with over 1500 released mutants of which less than 10% are chemically induced and more than 90% are induced by radiation. Insects compete with man for food and fibre and are a threat to animal and human health. In controlling insects with chemicals, we have sometimes created problems of environmental pollution and toxic residues in our food. Also, many insects have developed resistance to insecticides, often resulting in more insecticide being used. Therefore, new approaches to insect control are needed. One way of controlling or eradicating insects without the use of chemicals is the sterile insect technique (SIT). In this approach to insect control, insects are produced in large rearing plants, sexually sterilised using gamma radiation, and released into the native population. When the sterile insects mate with the wild insects, no offspring are produced. This approach is not only environmentally sound, frequently it is the only practical means of insect eradication. Sometimes the native population of the target insects is first reduced by cultural, biological or attractant/chemical methods before sterile insects are released. Then, when sterile insects are released, the ratio of sterile to native insects is high and the probability of a native insect mating with another native insect is low. If the ratio is high enough in an isolated situation, the sect will be eradicated from that area. SIT is

70

Chapter 4

most effective when the sterile insects can be produced in large numbers, and the native population is low and isolated from other infestations. It is an ideal way of eradicating new infestations of insects before they spread over large areas, but also it is effective in area-wide control of established populations. Further, pest-free zones of agricultural production can be maintained through the use of the SIT. SIT must be undertaken on an area-wide basis for an effective programme. Areawide control of key insects without heavy use of insecticides is often the most economically and ecologically sound approach to pest management. This usually involves an integration of several methods of insect control of which the SIT is often a component. The first successful eradication of an insect using the SIT was the screwworm, a devastating pest of domestic animals and wild life, on the island of Curaqao in 1954. Later the screwworm was eradicated from the USA and then Mexico. Texas ranchers alone estimate that the programme has saved them US$100 million annually. In 1998, the "New World screwworm" was reported in North Africa. This is the first report of this insect becoming established outside the Western Hemisphere. The SIT is the logical technology now being applied to eradicate this new introduction. Much of the fruit produced throughout the world is subject to fruit fly infestation. Fruit flies not only damage the fruit, but prevent countries infested with certain fruit flies from exporting their fruit to countries which do not have these flies. The Mediterranean fruit fly (medfly) has been eradicated from Mexico and the Melon fly from most of Okinawa using the SIT. In addition, several fruit fly introductions have been eradicated from the USA using the SIT. Research is being conducted to reduce the cost of sterile medfly production. IAEA has developed a genetic sexing strain so that only male flies are released. This increases the efficacy of the SIT and avoids "stinging" damage to fruit by sterile females. Tsetse flies transmit a disease causing nagana in cattle and sleeping sickness in man. These insects have prevented settlement and development of large areas of Africa. One species of tsetse fly has been eradicated from parts of Nigeria and three species from parts of Burkina Faso using the SIT. Certain groups of insects, such as moths, are seriously damaged by sterilising dosages of irradiation. Scientists have learned that some of these insects can be irradiated at lower doses which will not completely sterilise the insect, but their progeny will be sterile. This inherited, or F-1 sterility, is an effective way of controlling some insects. Infestations of the gypsy moth have been eradicated in several isolated locations in the USA using this technique. Table 4.3 lists previous and current use of the SIT technology (source: IAEA).

4.2.1.1 Food preservation One of the first priorities in the world is to have enough healthy food for everybody. Great trouble is being taken to fertilise the land, develop suitable mutants of basic crop plants, provide a suitable infrastructure adapted to the country and, generally, create the right circumstances for a good harvest. After that we have to do more to make sure that

Man-made Radioactivit3,

71

Table 4.3 Insect pests and the SIT Insect

Previous use

Current use

Screwworm

Curaqao, USA, Mexico, Puerto Rico, US Virgin Islands Italy(e), Peru(e), Mexico, USA (accidental introductions) Japan(e) Rota, Hawaii (e) Netherlands(e) USA/Mexico(e) Switzerland(e)

Guatemala, Belize, Libya

Mediterranean fruit fly Melon fly Oriental fruit fly Orion fly Mexican fruit fly Cherry fruit fly Other fruit flies Pink Bollworm Codling Moth Gypsy Moth Tsetse flies (4 species) Boll Weevil Sheep Blow fly Mosquitos Stable fly Tobacco hornworm

USA(e) Canada(e), USA(e) USA(e) Tanzania(e), Nigeria(e), Burkina Faso(e) USA(e) Australia(e) E1 Salvador(e) St. Croix St. Croix

Guatemala, USA (accidental introductions) Japan Netherlands (control) USA/Mexico (quarantine) Several countries(e) USA (quarantine) Canada (control) USA Nigeria

USA(e) USA(e)

Note: The table shows insect pests for which the SIT or a related genetic control method is being used, has been used, or is being developed. The objective is eradication unless otherwise noted. An (e) indicates an experimental pilot test.

the preciously grown food is preserved and protected against contamination and pests~an especially important priority for the developing world. For thousands of years this problem has been with us and preservation methods have evolved from the earliest days of sun-drying to salting, smoking, canning, freezing, heating, and the addition of chemicals. The latest addition to this list is irradiation--the exposure of foods to carefully controlled amounts of ionising radiation. Although a relatively new commercial process, food irradiation has been studied more thoroughly than any other food technology. More than 40 years of research have shown conclusively that there are no adverse effects from the consumption of irradiated food. In fact for many foods, preservation by irradiation has proved to be by far the best method. Table 4.4 summarises the general applications of food irradiation technology. All necessary rules and regulations to irradiate certain foods have been adopted by the relevant international authorities, but there is still some public reluctance over the acceptance of such foods. This is surely only temporary and in the future food irradiation will certainly develop to become one of the great benefits for mankind, and

72

Chapter 4

Table 4.4 General applications of food irradiation Purpose

Absorbed dose (kGy)

Products

0.05-0.15 0.15-0.50

Potatoes, onions, garlic, ginger root Cereals and pulses, fresh and dried fruit, dried fish and meat, fresh pork Fresh fruits and vegetables

Low dose (up to 1 kGy)

Inhibition of sprouting Incest disinfestation and parasite disinfection Delay of maturation

0.50-1.0

Medium dose (1-10 kGy)

Extension of shelf life Elimination of spoilage and pathogenic microorganisms Improvement of technological properties of food

1.50-3.0 2.0-7.0 2.0-7.0

Fresh fish, strawberries, etc. Fresh and frozen seafood, poultry and meat Grapes (increased juice yield), dehydrated vegetables (reduced cooking time)

High dose (10-50 kGy)

Decontamination of food additives and ingredients Commercial sterilisation (in combination with mild heat)

0-50 30-50

Spices, enzyme preparations, natural gum, etc. Meat, poultry, seafood, prepared food, hospital diet

food preservation by irradiation will be of the greatest importance to food products grown in many countries. What are the benefits of using irradiation? It can kill viable organisms and specific, non-spore forming, pathogenic microorganisms such as salmonella, or it can interfere with physiological processes; for instance it can be used for sprout inhibition of potatoes or for extending the shelf-life of fresh fruit. In short, irradiation of food is an alternative, and in some cases the only, method to: 9 eliminate many health risks in food; 9 enhance the quality of fresh produce; 9 improve the economy of food production and distribution; 9 reduce losses during storage or transportation; and 9 disinfect stored products such as grain, beans, dried fruit, and dried fish. Economically, one of the most important applications results in the extension of shelf-life, which is of utmost value to countries with warm climates like so many of the developing countries. The same is true for the reduction of losses through storage which are very heavy in some areas: some countries report 4 0 - 5 0 % post-harvest losses through infestation of staple foods like grains and yams. Most stored staple foods therefore are fumigated by chemicals when not irradiated. The present status of the worldwide application of food irradiation is shown in Table 4.5. At an international conference held in Geneva in December 1988 on the "Acceptance, Control of and Trade in Irradiated Food" a document was adopted outlining the

Man-made RadioactiviO,

73

Table 4.5 Examples of worldwide approved uses of irradiated foods and commodities Country

Product

Argentina Bangladesh Belgium Brazil Canada Chile China Cuba Denmark Finland France Hungary India Indonesia Israel Japan Korea, Rep. of Netherlands

Spices, spinach, cocoa powder Potatoes, onions, dried fish, pulses, frozen seafood, frog legs Spices, dehydrated vegetables, deep-frozen foods, including seafood Spices, dehydrated vegetables Spices, potatoes, onions Spices, dehydrated vegetables, onions, potatoes, chicken Potatoes, garlic, apples, spices, onions, Chinese sausage, Chinese wine Potatoes, onions, cocoa beans Spices Spices Spices, vegetable seasonings, poultry (frozen deboned chicken), Spices, onions, wine cork Spices, onions, potatoes Spices, tuber and root crops Spices, potatoes, onions, grains Potatoes Garlic powder, potatoes, onions Spices, frozen products, poultry, dehydrated vegetables, rice, egg powder, packaging materials Spices Potatoes, onions, garlic, spices Potatoes, onions, fruit, spices, meat, fish, chicken, processed products, vegetables Potatoes, onions Potatoes, onions, chicken, fruit, spices Onions, fermented pork sausages, potatoes Potatoes, onions, cereals, fresh and dried fruits and vegetables, meat and meat products, poultry, grains Spices, poultry, fruit Spices, cereals, meat, poultry

Norway Pakistan South Africa Spain Syria Thailand USSR USA Yugoslavia

benefits of food irradiation and recommending harmonisation of national procedures to facilitate international trade in such products. At last, therefore, all practical obstacles seem to have been removed which could hinder the rapid development of this most useful application of radiation to mankind in the very near future.

4.2.2 Medical applications Applications of radiation and radionuclides for human health followed rapidly in the wake of the discovery of X-rays by R6ntgen. Techniques which permitted the production of specific radionuclides in useful quantities were developed. Today, hardly a

74

Chapter 4

single major hospital exists in an industrialised country which does not have a department of radiology and a department of nuclear medicine, or which does not use an extensive array of laboratory radiochemical methods for the diagnosis and investigation of a wide variety of diseases. In nuclear medicine, a radionuclide--in a carefully chosen chemical f o r m J i s administered to the patient to trace a specific physiological phenomenon by means of a special detector, often a gamma camera, placed outside the body. The importance of nuclear medicine, which is now a recognised medical speciality by itself, may be seen from the fact than one out of every three patients attending a major hospital in an industrialised country benefits from some type of nuclear medicine procedure. Such procedures may, like an X-ray, provide us with a picture of some particular body organ or part of it. The essential difference is that in nuclear medicine the picture obtained provides a measure of the activity of some specific physiological or biochemical function in the body. Most nuclear procedures are of a diagnostic nature. In some instances, however, radionuclides administered to the patient are valuable therapeutic tools. For example, one in every three persons admitted to U.S. hospitals undergoes a nuclear medical procedure for diagnosis or therapy. Many of these procedures employ radioisotopes. Some of the more frequent uses of medical radioisotopes include diagnosis and treatment of several major diseases, sterilisation of medical products such as tissue grafts, nutrition research, and biomedical research into cellular processes. Radioisotopes play an important role in the diagnosis and treatment of disease: for example, technetium-99m is used in about 36,000 medical procedures each day in the United States. This radioisotope, which is produced from molybdenum-99, allows physicians to diagnose diseases of the brain, lungs, heart and other organs without exploratory surgery. It is also used in bone scans to identify cancer or stress fractures that cannot be seen in X-rays. Germanium-68 is needed to calibrate positron emission tomography equipment, which is used to diagnose some types of cancer. Yttrium-90 is used to treat non-Hodgkin's lymphoma, a type of cancer, and bismuth-213 is being studied as a potential treatment for a form of leukaemia. Alternative treatments, where they exist, generally require painful, costly, often repetitive surgeries. By reducing the need for such surgery, these and other medical radioisotopes save the public approximately $ 1 2 x 109 per year in the U.S. alone. 4.2.2.1 Radiopharmaceuticals In order to be able to trace a specific biological process in the body, or investigate the functioning of a body organ, it is necessary to make a careful choice of both the radionuclide and the chemical form in which it is administered to the patient. Such radionuclide preparations are called radiopharmaceuticals. Today, some 100-300 radiopharmaceuticals are in routine use for diagnosis, most of which are commercially available. The majority of these compounds are organic in nature (see Table 4.6 for details).

Man-made Radioactivity

75

Table 4.6 Radionuclides in clinical use Radio- Half-life nuclide

Decay process

Principal radiation (MeV) e

Production method

Usage

6Li(n,)3H

Whole body water Biochemical research Physiological research

xory

3H

12.26 yr

e-

0.018

11C 14C

20.3 min 5570 yr

e§ e-

0.97 0.155

0.511 -

l~ JC 14N(n,p)14C

13N

10.0 min

e§

1.20

0.511

12C(d,n)13N

150

2.05 min

J8F 24Na 32p 365

110 min 2.58 yr 14.45 d 87 d

0.511 0.511 1.37 -

42K

310-000 yr 12.5 h

1.74 0.63 1.39 1.71 0.167 0.71

14N(d,n)15O 160(ot,pn) 18F 23Na(n,y) 24Na

36C1

e§ e § EC eeee-, EC e-

43K

22 h

e-

2.0 3.6 0.83

45Ca

165 d 4.53 d

e e

475c

3.43

e-

5~Cr

27.8 d

EC

52Fe

8.3 h 2.7 yr 45d

+ e , EC EC e-

5SCo

267 d 71d

EC + e , EC

0.49

65Zn

245 d

-4e , EC

0.33

67Ga

78h

EC

75Se

120 d

EC

47Ca

+

55Fe 59Fe 57Co

0.25 0.69 2.00 0.44 0.60

0.81 0.27 0.46

Breath tests Physiological research Physiological research

31p(n,7)32 P 35Cl(n,p)35S

Cancer research Exchangeable sodium Therapy of polycythaemia Drug research

35C1(n,7)3 6C1

Physiological research

1.53

41K(n,7)42 K

Exchangeable potassium

0.37 0.61

4~

Exchangeable potassium

K

44Ca(n,7 ) 45Ca 46Ca(n,qt) 47Ca

Calcium kinetics Calcium kinetics

0.322

5~

0.511

52Cr(o~,4n )52Fe 54Fe(n,y) 55Fe 58Fe(n,y) 59Fe

Red cell labelling Glomerular filtration rate Bone marrow imaging Ferrokinetics Ferrokinetics

6~ 7Co 58N(n,p)58Co

Vitamin B12 absorption Vitamin B12 absorption

64Zn(n,7) 65Zn

Physiological research

65Cu(o~,2 n)67Ga

Location of neoplasms and abscesses Imaging of the pancreas and adrenal glands

m

1.31 0.16

0.006 1.10

51Cr

1.29

0.122 0.511 0.81 0.511 1.11 0.18 0.30 0.14 0.27

74Se(n,7)7 5Se

continued

76

Chapter 4

Table 4.6 (continuation) Radio- Half-life nuclide

Decay process

Principal radiation (MeV) e

81Rb

4.5 h

e +, EC

81mKr 77Br 82Br

13.5 s 58 h 35 h

IT e +, EC e-

90y

99Mo

64.4 h 67 h

ee-

99mTc

6h

IT

lln

2.8 d

ll3Sn 113mln 123I

$

+

2.27 0.45

79Br(ot,2n )81Rb

Radionuclide generator Lung function studies

0.190 0.520 0.55 0.62 0.78

m

75As(o~,2n )77Br 81Br(n,qt) 82Br

Extracellular water Extracellular water

89y(n,7)9~ Y

Treatment of arthritic joints Radionuclide generator

0.74

98Mo(n,7 ) 99M0 U(nf) ----)99M0

EC

0.141 0.17 0.25

l~

118 d

EC

0.26

112Sn(n,y )ll3Sn

104 m 13.3 m

IT EC

0.39 0.16

121Sb(,2 n)123I

+

Jl

0.44

Usage

xory 0.511

D

Production method

1.23

2 n) II lln

127I(p,5n ) 123Xe ._.) 123I 125I

60 d

EC

131I

8.1 d

e-

127Xe

36 d

EC

133Xe 137Cs 198Au

5.3 d 30 yr 65 h

eee-

2~

74 h

EC

0.61

0.34 0.51 0.96

0.035

124Xe(n,7 )125Xe 1251

0.36

!3~ )131Te 1311 U(nf)131Te ---) 1311

133Cs(p,2p5n)127Xe

0.17 0.20 0.38 0.081 0.662 0.41

U(nf) ----)133Xe U(t/t/c) ---)137 Cs 197Au(n,7) ~ 198Au

0.07

203Tl(p,3n) 201Pb ---) 201T1

Organ imaging (table 6.1) White cell labelling Imaging of cerebrospinal fluid Radionuclide generator Cardiac output Thyroid studies Renal studies Radioimmunoassay Plasma volume Effective renal plasma flow Deep vein thrombosis Thyroid studies Renal studies Treatment of thyrotoxicosis Treatment of thyroid cancer Lung function studies

Lung function studies Calibration source Treatment of intrapleural or intraperitoneal neoplasms Myocardial imaging

77

Man-made Radioactivity

To minimise the already small radiation dose to the patient through the use of diagnostic radiopharmaceuticals, more and more short-lived--or very short-livedw radioisotopes are being used. These short-lived radioisotopes decay to stable elements within minutes or hours. Radiopharmaceuticals of short-lived isotopes have to be produced at the hospital where they are to be used. This is often done by "milking" the desired isotope from a longer-lived radioactive parent. This is a relatively simple procedure, but it often must be followed by some rapid chemical procedures to convert it into the requisite radiopharmaceutical. This technique is used routinely in hospitals for diagnostic investigations of the functioning of the liver, brain, lung, heart or kidney. Short-lived radionuclides such as indium-111, gallium-67, gallium-68, thallium-201, and the most commonly used technetium-99m, find wide applications. New applications and radiopharmaceuticals are being developed to extend the range of procedures available to doctors. However, it must always be remembered that any in vivo nuclear medicine procedures involve a small radiation dose to the patient. As an illustration, we shall briefly discuss the production of 123I(after Witenboer et al., 1986). For commercial production of iodine- 123, two routes are currently used, viz. the direct reaction 124Te(p,2n)123I and the indirect reaction 127I(p,5n)123Xe ~ 123I. The iodine-123 produced is contaminated with other radioisotopes of iodine, the main contaminant in the first route is 124I, formed by the 124Te(p,n)124I reaction, and in the second route 125I,formed by the 127I(p,3n)~25Xe ---) 125Ireaction. Production of sizeable quantities of iodine-123 of higher purity is possible via proton irradiation of highly enriched xenon-124. The reactions leading to iodine-123 are: 124

Xe(p,2n) 1 23Cs

124Xe(p,pn)123Xe

(5.9 min) --~ 123Xe

(2.1 h) ---) 1231 (Q =-15.5 MeV)

(4.12a)

(Q =-10.3 MeV)

(4.12b)

(Q = -6.8 MeV)

(4.12c)

(2.1 h) -"-) 123I

124Xe(p,2p) 123I Reactions leading to other radioisotopes of iodine are: 124~t r

,,

- 120

Aetp,om)

I

124Xe(p,~)1211

(2.1 h) ---) 121Te

'24Xe(p,3He)122I 124Xe(p,p2n)'22Xe 124Xe(p,qt)125Cs

(20 h) ~ 1221 (45 min) --~ 125Xe (17 h) ~ 125I

(Q = -6.5 MeV)

(4.13a)

(Q = +3.8 MeV)

(4.13b)

(Q = -9.0 MeV)

(4.13c)

(Q =-18.7 MeV)

(4.13d)

(Q = +3.9 MeV)

(4.13e)

The cross section for the interfering 124Xe(p,~) reaction is relatively low, in the energy range of 27-20 MeV, so that only a minute 1251impurity is to be expected. Since

78

Chapter 4

iodine-120, iodine-121 and iodine-122 have short half-lives (1.35 h, 2.1 h, and 3.5 min respectively), no substantial contamination with these radioisotopes will be present at calibration time. Highly enriched xenon-124 is expensive (US $ 150,000 per litre STP) due to its natural abundance of only 0.096%. This calls for an effective gas target and a reliable gas handling system. In the past considerable experience has been obtained in handling enriched krypton-82 gas for the production of rubidium-81 for krypton-81m generators. Since June 1984 this technology is being applied and further improved for the production of iodine-123 via proton bombardment of the enriched xenon-124.

4.2.2.2 Diagnostic methods in cardiology Radionuclides play an important role in cardiological diagnosis. When a doctor examines the pulse of a patient, he is trying to gauge the blood flow, judge the condition of the blood vessel, and indirectly evaluate the force of the pumping action of the heart. A circulating radioactive tracer, like a small spy, can relay the same kind of information from within, such as what volume it occupies after dilution as a blood pool in the heart, and how this volume changes when the heart contracts. With the help of a computer, such information is obtained quantitatively and sequentially in relation to time. Such intelligence forms the heart of nuclear cardiology, one of the most useful applications of modem nuclear medicine. When a patient sees a doctor because of heart trouble, the doctor has many options depending on his suspicions. One rather elaborate way to diagnose is to inject a radiotechnetium compound into the blood stream, followed by an analytical method known as single photon emission computed tomography (SPECT). A rotating gamma camera measures the radioactivity at short intervals providing, with the help of a computer, a reconstructed picture, which enables the physician to determine how much of the heart muscle is deprived of blood. If the blood flow to the heart, as well as the metabolism of the muscle, are to be assessed, then another new method can be very useful. The positrons emitted from some radionuclides which have been incorporated in organic compounds are measured by positron emission tomography (PET). The positrons are produced when certain short-lived isotopes decay and, through interaction, produce very strong gamma rays (511 keV) which go off in almost exactly opposite directions. These can be detected easily by a special device using detectors placed on opposite sides of the patient. During the last few years, a much smaller and more sensitive detector has been developed which will make this method even more useful in the future. As a result of such measurements, one can show the distribution of the tracers, or rather the compounds containing these tracers, indicating how metabolically active these tissues are. Molybdenum-99 is a radioactive isotope that decays to form technetium-99m, an isotope used in about 36,000 medical procedures each day in the United States. Technetium-99m allows physicians to diagnose many conditions in the brain, lungs,

Man-made Radioactivi~

79

heart, and other organs without the use of dangerous and expensive exploratory surgery. For example, technetium-99m imaging is used to diagnose poor blood flow in the lungs and heart. Alternative diagnostic methods include an arteriogram, a procedure in which an imaging device is inserted into a large vein, and cardiac catheterization, which requires inserting a tube into the heart. These alternative methods cause the patient some discomfort and require a recovery period. Because technetium-99m imaging is not a surgical procedure, costs for surgical facilities and personnel, as well as medication to ease pain and promote healing, can be avoided. Technetium-99m is also used in bone scans to identify the spread of cancer to the skeletal system or to detect stress fractures that cannot be seen in X-rays. There are many other usable positron emitters, like rubidium-82, which are used to measure the blood flow to the heart muscle. There are other techniques as well, some using non-radioactive compounds by making use of the known X-ray computed tomography method. More recently, even magnetic resonance imaging methods are being applied for certain diagnostic work. Ultrasound techniques also are being tried for certain heart assessments. These examples illustrate that with sophisticated radiation-emitting methods, it is possible to make diagnoses which would have been impossible not so long ago. Roughly three percent of the population of Europe, some six million people, suffer from coronary artery disease. A routine procedure could involve many of them in tomographic tests using a radiopharmaceutical. Nuclear imaging is used more and more widely, such as for brain disease diagnosis. Cerebrovascular diseases occur at roughly the same rate as cardiac troubles. In these cases, organic radiochemicals are labelled with fluorine, oxygen, nitrogen or carbon radionuclides for imaging. Tumours may be located with similar methods, using either simple radiopharmaceuticals or complex radionuclide-labelled antibodies. As an example, let us discuss in some detail thallium-201 which is used as an agent for myocardial imaging studies. There is an ever-increasing use of thallium-201 (Z~ in nuclear medicine in the last two decades (Pennel et al., 1992). The 2~ given intravenously as thallous chloride is used in myocardial perfusion scintigraphy, because its rapid clearance from the circulating blood into the myocardial tissue reflects, reasonably well, the myocardial perfusion. Myocardial perfusion scintigraphy has gained worldwide acceptance as a non-invasive approach to the evaluation of patients with suspected coronary heart disease (Steien and Aaseth, 1995). The isotope, 2~~ is a cyclotron-produced radioactive compound, decaying to mercury-201 (2mHg) with a physical half-life of 73 h, the decay being accompanied by emission of gammaphotons of 135 and 167 keV, but the main emission is X-rays of 67-82 keV. After intravenous administration of a tracer dose of thallous-201 chloride, the cation disappears quickly from the circulation, with a biological half-life in the blood of less than 1 min, as the 2~ is rapidly taken up by different tissues, especially heart and skeletal muscle (Kazantzis, 1986; Pennal et al., 1992). In apparently healthy individuals subjected to standardised physical exercise on a bicycle ergometer before intravenous administration of 2~ chloride (80 MBq), it was found that 3.9% of the

Chapter 4

80 Table 4.7

Thallium-201 activity in various organs, given as percentage body burden (mean and range), at different time intervals after an intravenous injection of 80 MBq [2~ thallous chloride (after Steien and Aaseth, 1995) Organ

Heart Brain Thyroid Liver Kidneys Lower extremities

Time interval after 2~

injection

30s

4h

24h

3.9 (3.6--4.1) 1.4 (1.0-1.7) 0.8 (0.7-1.0) 3.5 (2.9-4.3) 6.5 (5.2-9.0) 42 (40-46)

2.2 (2.0-2.4) 1.4 (1.1-1.7) 1.2 (0.8-1.3) 3.4 (2.5-4.4) 6.0 (4.8-8.3) 38 (35-42)

1.8 (1.3-2.3) 2.1 (1.8-2.9) 1.1 (0.9-1.6) 3.6 (2.5-5.1) 6.0 (4.6-8.1) 31 (28-33)

dose was rapidly taken up by the heart (Table 4.7). The washout rate from the heart was relatively low, with 2.2% of the body burden being retained after 4 h and 1.8% after 24 h. In the thyroid gland, as in the brain, the uptake was rather small, and the 2~ deposits in these tissues were not subjected to apparent washout/redistribution during the observation period (Table 4.7). The lower extremities with their considerable amount of muscles showed the highest 2~ uptake (42%), and a significant washout was observed during the subsequent 24 h period. The hydrated thallous ion is similar in size to the hydrated potassium ion, and early literature reported that the uptake of T1 cations in muscle cells made use of the specific uptake mechanism developed for potassium. However, later studies, taking account of the complexity of potassium transport, and the different types of potassium channels, have found some differences between the cellular TI uptake and the potassium uptake. Thus, digoxin that inhibits the Na/K ATP-ase enzyme system as well as the potassium ion-transport, did not affect the 2~ transport. Furthermore, once inside myocardial or other cells, 2~ shows a low washout rate compared with potassium, probably owing to its interactions with intracellular constituents. The crucial physiological factor that interferes with the 2~ uptake by heart muscle cells, in vivo, is local hypoxia. Thus, hypoxia induced by physical stress in patients with coronary heart disease, can be scintigraphically visualised at 2~ uptake defects, provided that the imaging is performed soon after the isotope injection. After a redistribution period of 3-4 h, the 2~ uptake is accomplished even in poorly perfused muscle cells, indicating that the 2~ distribution after a 3 h equilibration period will reflect the viable mass of the myocardium. 4.2.2.3 Radionuclides in the treatment of disease

There are relatively few situations in which the administration of a radiopharmaceutical to the patient can be used for treatment of disease. The oldest and best known of these applications is the treatment of overactivity of the thyroid gland and of some types of

Man-made Radioactivi~'

81

thyroid cancer, by giving the patient a carefully calculated amount of iodine- 131. Other examples are the use of strontium-89 to palliate pain provoked by bone metastases of prostatic, mammary and possibly other carcinomas; or the treatment of phaeochromocytoma and other tumours of the cromoffin tissue with iodine-131 labelled metaiodobenzyl-guanidine. Much hope for the future lies in the development of tumour-specific antibodies which could be used to target radionuclides to tumours and thereby destroy them. Teletherapy is radiation treatment where the radiation source is not in direct contact with the tumour to be treated. The radiation used for the treatment can be of different types and energies and originate from different sources. Gamma-emitting radioactive sources such as cobalt-60 are often used, because they are convenient, need virtually no maintenance, and are almost ideal gamma emitters. Many of these sources are in use for cancer treatment. Brachytherapy is a treatment where the radiation source is in direct contact with the tumour. This method is used widely for a number of special medical cases. As cancer of the cervix is quite a common disease in many developing countries, brachiotherapy has become the method of choice for treatment because many patients can be treated relatively cheaply and effectively. One of the first big projects of this kind in a developing country was organised in Egypt with the co-operation of the World Health Organisation (WHO) and the IAEA. This method, however, is only applicable when the tumour has not spread more than a few centimetres. Fortunately, this is the case with many patients. Should the tumour be larger however, the more costly teletherapy must be applied. The usefulness of brachytherapy for cancer treatment can be assessed when one realises that roughly one quarter of all cancer cases in countries like Nigeria are suitable for such treatment. With a relatively inexpensive and uncomplicated application of radiobrachytherapy, one can not only treat but, in especially early cases, also cure many patients. In the last two decades, scientists have developed homing materials (monoclonal antibodies, peptides) that attach themselves to various types of cancer cells. Methods of linking radioactive isotopes to these homing materials have also been discovered, resulting in so-called "smart bullets" that can be delivered directly to the locations of cancer cells. Scientists have demonstrated this procedure by attaching yttrium-90, a beta-emitter, to a monoclonal antibody as a potential treatment for non-Hodgkin's lymphoma, a type of cancer, with very positive results. Researchers are now assessing yttrium-90 for use in treating many types of cancers. Together, these cancers are diagnosed in an estimated 210,000 people each year in the U.S. alone. Since alpha particles have a smaller range than beta particles, by using them the radiation is delivered to cancer cells without damaging surrounding healthy tissue. The successful use of alpha-emitters for cancer therapy depends on the identification of a homing material for each type of cancer to be treated. Chemical processes that can attach an alpha-emitter to the desired homing material must also be found. If this therapy proves successful, specific alpha-emitters must be produced at a large rate that allows for full-scale treatment of affected populations.

82

Chapter 4

Three alpha-emitters, bismuth-213, astatine-211, and radium-223, have been shown to have the properties needed for cancer therapy. All three have been successfully linked to a homing material. Pre-clinical trial results have been promising. Clinical human trials for treatment of a type of leukaemia began at New York City's Memorial Sloan Ketting Cancer Center in October 1996. The University of California at Los Angeles is also studying bismuth-213 for lung cancer therapy. The National Cancer Institute is conducting studies to determine the value of this therapy in treating brain cancer. Pre-clinical trials Using astatine-211 for brain cancer therapy have been initiated at Duke University Medical Center. Studies using radium-223 are under way at Pacific Northwest National Laboratory, Idaho State University, Washington State University, the New Jersey School of Medicine, and UCLA. If the use of alpha-emitters for cancer therapy proves successful, it has been estimated that some 30-50,000 cancer patients could be treated in the United States each year.

4.2.3 Industrial applications Many beneficial applications of radiation and radioisotopes in industry are well established. Use of radioisotopes and radiation in modern industry is of great importance for process development and improvement, measurement and automation, and quality control. Today, almost every branch of industry uses radioisotopes and radiation in some form. The use of radioisotope thickness gauges is a prerequisite for the complete automation of high speed production lines such as for steel-plate or paper. Tracer experiments give exact information on the condition of expensive processing equipment and increase its usable life. The use of isotopes has grown rapidly in virtually all industries. For dams, aircraft, bridges, and piping, isotope use has become critical to ensuring structural integrity. As an example, let us mention that radioisotopes are the only tool available today for scanning the interior structure of a jet engine or an oil pipeline to detect flaws prior to failure. Several radioisotopes are used to ensure safety in industry and transportation. For example, iridium-192 is used to verify the structural integrity of aircraft, ships, bridges, and other structures, for weld inspection, and other purposes. Californium-252 is used to gauge the moisture content of soil in road construction and the building industries. Various isotope applications are used to monitor the quality of materials and structures. Isotopic tracer techniques measure wear, corrosion, moisture, leakage, and many other factors. Neutron radiography creates images of materials that are not as dense as those captured in X-ray photos. This method is used chiefly to check uranium fuel in nuclear reactors for flaws, to find cracks in the inner plastic or aluminium parts of airplanes, or to detect tiny fissures in gas turbine blades. Californium-252 is used for neutron radiography and neutron activation analyses. Some of the more common industrial uses of isotopes to ensure safety include" 9 wear and corrosion analysis;

Man-made Radioactivi~'

9 9 9 9

83

leak, flaw, and malfunction investigations; elimination of static electricity; light sources for space and other remote locations and emergency lighting; and smoke detectors.

4.2.3.1 R a d i o i s o t o p e s as tracers

The fact that minute amounts of radioactive substance can be measured readily and precisely makes radioisotopes an important tool for investigations in which transport of material is involved and exact information about spatial and temporal distribution of the material is required. A wide range of different industries use tracer techniques including: 9 coal, 9 oil, gas and petrochemical; 9 cement, glass, building materials; 9 ore processing; 9 pulp and paper, iron and steel; 9 non-ferrous metals; and 9 automotive. The main areas where radioisotope tracers may be used are: 9 p r o c e s s i n v e s t i g a t i o n s - - r e s i d e n c e time, flow rate, velocity, modelling, parameter estimation; 9 m i x i n g m m i x i n g time, mixer optimisation, mixer performance; m a i n t e n a n c e - - l e a k detection, investigation of malfunctions, material transport; 9 w e a r a n d c o r r o s i o n m e n g i n e wear corrosion of process equipment, lubrication studies. 9 In the processing industries, one of the major applications of radioisotope tracers is for residence time investigations in which important parameters for plant optimisation, modelling, and automation are obtained. Once optimum performance of the plant has been reached, tracer experiments may be carried out to indicate deviations from optimum conditions. Often the reasons for malfunction are found, like unwanted by-pass streams, or obstruction of vessels and pipes which can cause changes in flow-rate or the appearance of dead zones. Often the necessity for a shut-down can be tested and vital information for repair work to be done can be obtained prior to shut-down. Typical examples are reported from the petrochemical industry for the optimisation of fractionating columns. Mixing is a very important step in some processes. It consumes time and energy and expensive equipment is necessary. Optimisation of mixing processes, therefore, is an important goal that can be reached by the application of tracers. The study of wear on machine parts, which were labelled by radioisotopes, is an important stage in the development work of the automotive industry. The design of a new motor necessitates hundreds of wear tests to be carried out. These tests can be made by using the radioisotope tracer technique. The surface activation technique, in 9

84

Chapter 4

which only a thin layer of the part under investigation is activated by bombardment with ions from an accelerator, guarantees extremely high sensitivity and uses only small amounts of radioactive material. Impressive figures are available concerning savings in the automotive industry due to the use of radioisotope tracers for wear studies. Reports say that in the development of a new engine the costs for testing a new cylinder liner amount to about US $360 000 for each liner when using conventional wear measuring methods. By using radioisotope tracer techniques, the costs are cut below US 50 000. For a series of measurements on 10 linear modifications, which are usually made during the development process, the savings made by applying radioisotope techniques would be around US$ 3,100,000. Similarly, the savings can be calculated for tests on bearing cups. For a series of tests on 20 beating-cup modifications, the costs amount to US$ 3,500,000. When applying radio-isotope techniques, the same results can be obtained for only US $ 400 000 resulting in a saving of US $ 3,100,000 (after IAEA Report). In addition to savings, there are further technical advantages of great importance. When using radioisotopes, the entire test can be run without dismantling the engine which allows more accurate results to be obtained. A very important factor in development is time. The results from the test series using radioisotopes are usually available within six months; the conventional tests may take up to five years. In general, tracer techniques are used throughout industry to improve the efficiency of the processes, to save time, energy and raw material, to reduce down-time of equipment, and to facilitate development work.

4.2.3.2 Radioisotope instruments The greatest impact of radioisotopes in industry has resulted from the use of radioisotope instruments. Due to the nature of the ionising radiation emitted from radioisotopes, a few unique advantages are provided with this technique: 9 Because radiation has the ability to penetrate matter, measurements can be made without direct physical contact of the sensor with the material being measured. 9 On-line measurements on moving material can be made; measurement is nondestructive. 9 The stability of the source is excellent and little maintenance is required. 9 Excellent cost/benefit ratios can be achieved. Radioisotope instruments became available for all kinds of measurements just when the trend towards automation in industry was strong. Radioisotope instruments can perform certain measurements such as mass per unit area which cannot be made by other equipment. For other measurements, like level or distance, there are now other competing methods available. Radioisotope gauges for measuring mass per unit area (sometimes also called "thickness gauges") are unequalled in their performance and are used in almost every kind of industry in which sheet material is produced. In the paper industry, not only the mass per unit area of the paper sheet itself is measured by radioisotope gauges, the

Man-made Radioactivity

85

production of the felt, which is used to support the still very wet pulp in the first stages of paper production, relies heavily on the use of radioisotope gauges to guarantee its extreme uniformity, as well. The latter is of vital importance for the paper machines operating at high speed. Similarly, the production of steel plate at the speed of modern rolling mills could not be done without accurate measurement of thickness at every moment of the production and automatic control of the rolling stands. In the plastics industry, radioisotope gauges are used to improve the uniformity of the product, and hence savings can be made in raw material and in energy needed for production. Microprocessor technology had a great impact on the development of radioisotope instruments. Linearisation of complex calibration curves, compensation for the decay of the radioisotope, and performance of important calibration checks can be handled easily by the microprocessor. In this way, radioisotope instruments of modern design added yet another dimension of reliability and sophistication to their proven excellence. Density gauges based on the absorption of gamma radiation are used wherever the automatic determination and control of the density of liquids, solids, or slurries is important. The oil industry relies heavily on such instruments. Other applications are in the handling of slurries in mineral processing or even in the food industry. One of the earliest users of radioisotope instruments was the tobacco industry, where density gauges make sure the right amount of tobacco is packed into each cigarette. The coal industry has benefited greatly through the applications of nuclear techniques. Nucleonic gauges and on-stream analysers are now regularly employed for monitoring and controlling the ash and moisture content in coal and coke. Nuclear techniques make possible the on-line determinations of sulphur and nitrogen (the causes for acid rain) in coal; both of these are important for pollution control. Hundreds of millions of tonnes of coal are analysed annually by this method, a process which has become routine in the coal industry. Radiation from radioisotope sources can be used to excite characteristic X-rays in samples upon which the beam of radiation is directed. Detection and analysis of these X-rays yield information about the composition of the sample. This opens the field of analytical applications of X-ray fluorescence analysis. The most frequent applications are in the ore processing and the metal coating industries. In ore processing, a sample stream of the slurry of ground ore is fed to a measuring head containing the radioisotope source and the X-ray detector. The exact composition of the slurry can be determined and the operation of the plant controlled to give optimum performance. Great savings can be achieved by better utilisation of raw ore, energy, and chemicals used for the process. Although the cost of such an instrument, including installation, is high it can be recovered usually within one year of operation. In metal coating, such as galvanising or tin-coating of steel plate, the exact amount of coating must be applied. A surplus of material is extremely expensive; undercoating results in complaints and early corrosion. Through the use of radioisotope gauges,

86

Chapter 4

coating processes can be controlled to meet tight limits and thus up to 10% of material (zinc, tin) can be saved. At the same time, the reject rate due to undercoated strip is reduced. In the production of sheets and plates cut to a certain length, special steps are taken to measure the exact length of material when it passes the gauge. Digital counting techniques are preferred for this type of measurement because the timing of the measurement can be made to fit exactly the desired stretch of material. Level measurements can be made by installing a source and a detector on opposite sides of a tank or silo. When filled, the material absorbs the radiation otherwise sensed by the detector. This technique is most useful where circumstances such as pressure, heat, or the presence of toxic, corrosive, or abrasive substances make access to the tank and installation of conventional gauges difficult or impossible. Level gauging using movable source detector combinations is a useful tool for the inspection of process equipment such as chemical reactors. Checking catalyst levels in chemical reactors or monitoring the operation of large fractionating columns in refineries are two applications widely used. Again, savings can amount to impressive figures if one considers that down-time costs due to production losses of a distillation column in a petroleum refinery can be in the order of US$ 300 000 per day (IAEA Report). Yet another extremely useful application of radioisotopes which can save considerable costs and prevent severe damage is in quality control during the construction of pre-stressed concrete bridges. The strength of these bridges is based on bracing cables which run through encasing tubes in the bottom section of the bridge girder. If the bracing cables do not lie in a straight line, considerable damage to the building may result when the necessary stress is applied to the cables. Parts of the concrete slab may be caused to fly off due to the unexpected forces, representing not only a severe hazard, but also necessitating a complete reworking of the structure. A radioisotope source, which is inserted into the encasing tubes and pulled through before the bracing cables are pulled in, is used to determine the exact position of the tubes. If any deviation from their target position is observed, corrective measures may be taken before damage to the building occurs. Such deviations can originate when the encasing tubes are detached from their fastenings by the force of the concrete cast into the sheathing. Neutron moisture gauges are especially well suited for measuring moisture in bulk material such as sand. Their use in the production of glass and concrete continues to grow. Portable instruments are indispensable for checking thicknesses of bituminous material in the construction of roads and dams. A gamma density measurement completes the important information about the quality of the construction. A novel, routine use of neutron sources is in the rapid detection of hidden explosives. Instruments have been developed that can detect small amounts of explosives by measuring gamma rays emitted when neutrons are captured by nitrogen atoms which are present in explosives. Nuclear techniques such as nuclear bore-hole logging and radiometric in-situ analysis play an increasingly important role in the exploration for oil, gas, and metalliferous minerals.

Man-made Radioactivity

87

Radiography using x- or gamma-rays is well established and is a routinely used technique of non-destructive quality control. It is applied for checking welds, castings, assembled machinery (such as jet engines), and in ceramics. Radioisotopes as a source of radiation offer the advantage that they do not require electrical power so that they can be used readily in the field. Different sources are available as well, ranging from low to high energy. The small size of radioisotope sources allows inspection of parts or machinery which could not be examined by X-ray tubes. The most frequent application of gamma radiography is checking the welds in pipelines. This is done most conveniently by putting the source inside the centre of the pipe and attaching the film to the outside of the weld. For checking long pipelines, sophisticated, self-propelled crawlers which travel in the pipe are used. These devices can be positioned exactly at the desired position from the outside. At a command the exposure is made. Then the crawler is instructed to move on to the next weld. Practically all new gas- or oil-pipeline systems are checked with this type of equipment. 4.2.3.3 Radiation in manufacturing Radiation can induce certain desired chemical reactions. It can, for example, be used in the making of plastic, or to graft plastic to other materials. Some polymers whose cross-linkage is induced by radiation can be tailored to shrink when heated--a desirable property in some packaging applications. The wood and printing industries make extensive use of electron-beam radiation to cure surface coatings. The rate of production of wire and cable insulated with radiation cross-linked polyvinylchloride is increasing steadily. Such insulation has better resistance to heat and chemical attack and increased cut-through resistance, and is more compact. The products are used in the automobile industry, telecommunications, the aerospace industry, and in home electrical appliances. Other important products include radiation cross-linked foamed polyethylene which is used for thermal insulation, floor mats, crash padding, floating jackets, and wood/plastic composites cured by gamma irradiation. These have been used successfully for flooring in places such as department stores, airports, hotels, and churches where their excellent abrasion resistance, the beauty of the natural grain, and low maintenance costs are important. This latter technique is also being used in the conservation of objects made of stone and wood of interest to our cultural heritage. The vulcanisation of rubber sheet by radiation--instead of using sulphur in the manufacture of tyres--is being used commercially by several tyre companies. A "super-absorbent" material manufactured by radiation grafting techniques has come onto the market recently. The material is capable of absorbing and holding large amounts of liquid. Products manufactured from it include disposable diapers, tampons, and air-freshener elements. Radiation is beginning to be used to decompose septic or poisonous waste. Some cities irradiate human waste products. Radiation replaces the otherwise necessary addition of chemicals such as chlorine, itself a poison.

88

Chapter 4

Radiation processing has great potential in a new area of application known as radiation immobilisation of bioactive materials such as drugs, enzymes, antigens, and antibodies on polymeric materials. Such immobilisation assures better stability and longer shelf-life for the sensitive biological molecules and offers the possibility of producing slow and sustained drug delivery systems for prolonged controlled therapy of many diseases.

4.3 MANUFACTURING OF RADIOISOTOPES Radioisotopes, as well as stable isotopes, can be produced by accelerators, mainly cyclotrons, reactors or by devices constructed for isotope separation. In this chapter we shall mention some of the most important locations in several countries which are in the business of manufacturing and selling isotopes. 4.3.1 U.S.A. Although there are several private isotope production facilities we shall mention here only isotope production and distribution carried out by the U.S. Department of Energy (DOE). The U.S. Department of Energy's national laboratories offer unique isotope production and separation facilities and processes, such as reactors, associated hot cells, accelerators, and calutrons. The location of these laboratories is shown in Fig. 4.2.

Fig. 4.2. United States Department of Energy isotope origins.

Man-made RadioactiviO,

89

The production, acquisition and distribution of isotopes, and performance of related services, continue long-standing activities conducted by the United States Department of Energy and its predecessor agencies. Materials in inventory or produced in nuclear reactors, charged particle accelerators and separated stable isotopes, DoE offers for sale. The isotopes are mostly in intermediate forms suitable for incorporation in diverse pharmaceuticals, generator kits, irradiation targets, radiation sources, or other finished products. The 85-megawatt High Flux Isotope Reactor at Oak Ridge National Laboratory provides the world' s highest steady-state neutron fluxes. The neutron currents from the four horizontal beam tubes are also very high. The reactor operates about 43 weeks per year, and is used primarily to produce transuranic isotopes. Built-in experimental irradiation facilities also provide versatility, significant experimental capabilities, and the capability of producing a wide variety of isotopes. Products produced at this facility include californium-252, used primarily for cancer therapy, and iridium-192, used for industrial radiography. Sandia National Laboratories' Annular Core Research Reactor (ACRR) is a 2 megawatt, pool-type research reactor that is used to produce isotopes for medical applications. The ACRR and Sandia's nearby hot cell facility, along with Los Alamos National Laboratory' s (LANL) chemistry and Metallurgy Research Facility, have been chosen for US domestic production of molybdenum-99 and related medical isotopes. In addition, the US DoE processes byproducts from nuclear operations to obtain isotopes. For example, Pacific Northwest National Laboratory obtains yttrium-90 from strontium-90, a waste product. Researchers throughout the U.S. are now assessing the effectiveness of yttrium-90 in treating prostate and many other types of cancers. The Isotope Production Facility at LANL operates about 22 weeks per year. This accelerator facility produces radioisotopes using either the primary proton beam or neutrons from the beam stop of the Los Alamos Neutron Science Center (LANSCE), a halfmile-long accelerator that delivers medium energy protons. The unique characteristics of the LANSCE accelerator include a high energy, high beam current that allows production of higher quality radioisotopes, as well as exotic radioisotopes that cannot be produced in other facilities. Three major products produced at the site are germanium-68, a calibration source for positron emission tomography (PET) scanners; strontium-82, the parent of rubidium-82, used in cardiac PET imaging; and sodium-22, a positron-emitter used in neurologic research. The Brookhaven Linear Isotope Producer (BLIP) at Brookhaven National Laboratory uses a linear accelerator that injects 200 MeV protons into the 33 GeV Alternating Gradient Synchrotron. The BLIP facility operates about 16 weeks per year and produces radioisotopes such as strontium-82, germanium-68, copper-67, and others that are used in medical diagnostic applications. The electromagnetic calutrons at Oak Ridge National Laboratory separate isotopes with the same atomic number, but different mass, to produce enriched stable isotopes. During this process, mixed isotope material is vaporised (heated) and then ionised. The ionised particles are accelerated, and their trajectories are bent by a magnetic field. The

90

Chapter 4

Fig. 4.3. The U.S. Departmentof Energy isotope sales by production category. lighter particles separate from the heavier particles as they travel in an arc and are deposited on collectors, from which they are removed, chemically purified, and stored. The Oak Ridge National Laboratory's calutrons operate as needed to maintain an appropriate inventory of enriched stable isotopes. Many of these isotopes, such as strontium-88, thallium-203, and zinc-68, are required to produce other isotopes used to help diagnose cancer and heart disease and provide cancer therapy. Only one bank of calutrons is expected to operate during fiscal years 1998 through 2000. The contact point for information in this field is: 9 U.S. Department of Energy Office of Isotope Production and Distribution, Room A430 GTN, Washington, DC 20585, USA. Telephone: (301)903-5161; Fax: (301)903-5434; Telex: (710)828-0475. Two separate Government operations which supply products are: 9 The New Brunswick Laboratory Reference Materials Sales, Bldg. 350, 9800 South Cass Avenue, Argonne, IL 60439, USA. Telephone: (708) 972-2767; Fax: (708) 972-6252. 9 National Institute of Standards and Technology Radioactivity Standards Reference, Sales Office, Bldg. 245, Rm C114, Gaithersburg, MD 20899, USA. Telephone: (301) 975-5531; Fax: (301) 926-7416 It might be of interest to present a complete list of isotopes produced by DoE facilities; this is shown in Table 4.8. It is also interesting to see the distribution of isotope sales by production category: around 60% of radioisotopes are for medical use (as shown in Fig. 4.3.). Finally, let us mention that a variety of anodised, electroplated, deposited and polysurface disc and large area planar alpha and beta standards are available from: 9 Isotope Products Laboratories, 1800 N. Keystone Street, Burbank, CA 91504, USA. Telephone: (818) 843-7000 Fax: (818) 843-6168.

Man-made Radioactivio,

91

Table 4.8 Isotopes produced by DoE facilities Element

Radioisotope

Actinium-227

Ac-227

Aluminium

A1-26

Americium

Am-241 Am-243

Stable isotope

Natural target

Sb-121 and -123

Antimony

Ar-36 to 40

Argon Arsenic

As-72 As-73 As-74

Astatine

At-211

Barium

Ba-133g -133m

Berkelium

Bk-249

Beryllium

Be-7

Bismuth

Bi-205 -206 -207

Ba-130 to -138

Natural target

Natural target

Boron Br-76 -77 -80m

Br-79 and -81

Cadmium

Cd-109

Cd-106 to -116

Caldium

Ca-45

Ca-40 to -48

Californium

Cf-249 Cf-252

Carbon

C-14

C-12 and C-13 Natural target

Cerium

Ce-141

Ce-136 to-142

Caesium

Cs-137

Natural target

Chlorine

C1-36

C1-35 and-37

Chromium

Cr-51

Cr-50 to -54

Cobalt

Co-60

Natural target

Copper

Cu-64 Cu-67

Cu-63 and-65

Bromine

tp

pp

C1-35 and-37

Chlorine

continued

Chapter 4

92

Table 4.8 (continuation) Element

Radioisotope

Curium

Cm-244 Cm-248

Dyprosium

Dy-165

Stable isotope

Dy-156 to-164

Erbium

Er-162 to -170

Europium

Eu-151 and -153

Fluorine

F-18

Natural target

Gadolinium

Gd-153

Gd- 152 to - 160

Gallium

Ga-67

Ga-69 and -71

Germanium

Ge-68

Ge-70 to -76

Hf-172

Hf- 174 to - 180

Hydrogen

Deuterium

Tritium

Indium

In-114m

In-113 and -115

Iodine

1-124 1-125

Gold Hafnium

Natural target

Helium-3

He3-Rg & Pg, He3995

1-129 Iridium

Ir-192

Ir-191 and -193

Iron

Fe-52

Fe-54 to-58

Fe-55

Fe-59 Krypton

Kr-85P Kr-85E

Lanthanum Lead

Kr-78 to-86 La- 138 and - 139

Pb-203

Lithium

Pb-204 to -208 Li-6 and-7 Natural target

Lutetium

Lu- 175 and - 176

Magnesium

Mg-28

Mg-24 t o - 2 6

Manganese

Mn-54

Natural target

Mercury

Hg-203

Hg- 196 to -204

Molybdenum

Mo-92 to - 100

Neodymium

Nd-142 to-150

Neon

Ne-20 to -22

continued

Man-made Radioactivi~.

93

Table 4.8 (continuation)

Element

Radioisotope

Neptunium

Np-236 Np-237

Nickel

Ni-63

Ni-58 t o - 6 4

Niobium

Nb-95

Natural target

Nitrogen Osmium

Stable isotope

N-14 a n d - 1 5 Os- 194

Oxygen

Os- 184 to - 192 O-16 to -18

Palladium

Pd-103

Phosphorus

P-33

Platinum

Pt-195

Plutonium

Pu-237 Pu-238 Pu-239 Pu-240 Pu-241 Pu-242

Polonium

Po-210

Pd-102 to -110 Pt- 190 to-- 198

Potassium

K-39 to -41

Praseodymium

Natural target

Promethium

Pm-147

Radium

Ra-224

Rhenium

Re-186

Re- 185 and - 187

Re-188 Rubidium

Rb-83

Rb-85 a n d - 8 7

Ruthenium

Ru-97

Ru-96 to - 104

Samarium

Sm-145 Sm-153

Sm-144 t o - 1 5 4

Scandium

Sc-47

Natural target

Selenium

Se-72 Se-75

Se-74 t o - 8 2

Silicon

Si-32

Si-28 t o - 3 0

Na-22M Na-22S

Natural target

Silver Sodium

Ag-107 a n d - 1 0 9

continued

Chapter 4

94

Table 4.8 (continuation)

Element

Radioisotope

Stable isotope

Strontium

Sr-82

Sr-84 to-88

Sr-85 Sr-89 Sr-90 Sulfur

S-35

S-34 and-36 S-32 t o - 3 6 Ta- 180 and - 181

Tantalum

Ta-182

Technetium

Tc-95 Tc-95m Tc-96 Tc-99

Tellurium

Te-127

Terbium

Te- 120 to - 130 Natural target

Thallium

T1-204

Thorium

Th-229

Thulium

Tm-170

Natural target

Tin

Sn-117m Sn-119m

Sn-112 to -124

Titanium

Ti-44

Ti-46 t o - 5 0

Tungsten

W-188

W- 180 to

Uranium

U-233 U-234 U-235 U-236 U-238

Fissile target

TI-203 and-205

- 186

Vanadium

V-48 V-49

V-50 to -51

Xenon

Xe-127

Xe- 124 to - 136

Xe-133 Ytterbium

Yb- 169

Yttrium

Y-88 Y-90

Zinc

Zn-62 Zn-65

Zn-64 t o - 7 0

Zirconium

Zr-88

Zr-90 to -96

Yb-168 to-176

Man-made Radioactivity

95

4.3.2 France

The Bureau National de M6trologie (BNM) has designated The "Laboratoire de Messure des Rayonnements Ionisants" (LMRI) as "Approved Calibration Center". It is a laboratory of the "Commisariat a l'Energie Atomique (CEA)" implanted in the Nuclear Research Center of Saclay. It belongs to the "D6partement des Applications et de la MEtrologie des Rayonnements Ionisants" (DAMRI) whose laboratories are specialised in radioactivity for research and industrial applications of radionuclides. In addition, the LMRI elaborates and distributes radioactivity standards and references, and provides calibrations, measurements and testings in radioactivity and dosimetry, for measuring instruments and ionising radiation sources. These services are intended for research, industry and medicine. The certified values of the produced standards are linked to the national standards by the Primary Laboratory of the "Bureau National de MEtrologie". This traceability is achieved through the utilisation of measuring instruments which are periodically calibrated standards provided by the Primary Laboratory. At international level, traceability is established for a certain number of radionuclides, with national laboratories with which the Primary Laboratory performs direct comparisons or indirect comparisons through the International Reference System of the "Bureau International des Poids et Mesures". An official calibration certificate containing all necessary information is provided with each standard. Because of some physical or chemical phenomena, such as, for example, adsorption in wall containers, the quality of a standard deteriorates with time. In addition, due to the uncertainty about the half-life, it is recommended not to use a standard beyond a certain space of time. This time is twice as long as the half life for radionuclides with "short half life" (T~/2 < 1 year) and 1 year for those with "long half life" (T1/2 -> 1 year). According to official regulations, solid standard sources are generally submitted to classical tests of non-contamination by wiping or by immersion, as required. However, in view of the meteorological quality required, some standards being brittle and of low level activity, these tests are not performed in order to avoid any alteration of the standards or of their accuracies. On the other hand, the sealed sources are submitted to strict tests. The radionuclides which can be fabricated together with their characteristics (lifetime energies of emitting radiation) are shown in Table 4.9. Radioactive standard solutions are usually supplied in sealed glass ampoules. However, for high activities, standards are supplied in capped glass vials for easier handling. For safety, large volume standard solutions for environmental survey are delivered in plastic vials. Multigamma standard solutions differ from other solutions by the fact that they are characterised in terms of photon emission flux per unit mass in 4rt sr (expressed in s-~ g-~). The energies of gamma-rays given as reference are also certified. For calibration, either in energy or in efficiency of NaI(T1) or Ge(Li) detectors, the following compositions are proposed:

96

Chapter 4

Table 4.9 Radionuclides and radiation energies (MeV)

Radionuclide

T1/2

1l~

2.50X102 days

l l0Ag

(x

~max

it

2.235 2.892

0.658 0.706 0.764 0.885 0.937 1.384 1.505 1.808 0.060

26A1 241Am

7.16x 105 years 4.33x102 years

195Au

1.83x102 days

198Au

2.70 days

133Ba

1.05•

7Be 2~

5.32x101 years 3.28x101 years

82Br

3.53•

hours

0.265 0.445

14C

45Ca

5.73• 103 years 1.63• 102 days

0.156 0.257 0.257

l~176

4.63•

139Ce 14ICe

1.174 5.443 5.486

XK

0.030 0.099 0.129 0.412 0.676 0.081 0.161 0.223 0.276 0.302 0.356 0.384 0.477 0.570 1.063 1.770 O.554 0.619 0.698 0.777 0.827 1.044 1.317 1.475

0.067

days

0.088

1.38• days 3.25x101 days

0.166 0.145

0.022 0.026 0.033 0.036

0.285 0.961

! years

0.435 0.580

0.072 0.031 0.035

0.075

Man-made RadioactiviO'

97

Radionuclide

T1/2

~max

144Ce+144pr

2.85x 102 days

0.185 0.238 0.318 2.996

252Cf

9.67• 102 days

36C1 244Cm

3.01 x 105 years 1.81xlO 1 years

57Co

2.72x 102 days

58Co

7.08x101 days

0.475

60Co

1.93x103 days

0.318

5~Cr

134Cs

2.77x101 days 7.55x102 days

137Cs+137mBa

3.02x101 years

169Er

9.40 days

J52Eu

1.35x 101 years

6.075 6.118

XK 0.080 0.134 0.697 1.489 2.186 0.043 0.100

0.036

0.014 0.122 0.136 0.811 0.864 1.675 1.173 1.333 0.320 0.563 0.569 0.604 0.796 0.802 1.168 1.365 0.662

0.006

0.709 5.666 5.763 5.805

0.089 0.415 0.658

0.511 1.173 0.343 0.352 0.387 0.698 1.475

0.006

0.005 0.032

0.032

0.008 0.122 0.245 0.296 0.344 0.411 0.444 0.689 0.779 0.867 0.964 1.086 1.112 1.213 1.299 1.408 continued

Chapter 4

98

Table 4.9 (continuation) Radionuclide

TI/2

55Fe

9.79x 10 2 days

59Fe

4.45x101 days

67Ga

3.26 days

3H 2O3Hg

1.23x101 years 4.66x101 days

0.018

166mHo

1.20x 10 3 years

1231

XK

~max

0.006 0.007

0.273 0.466

0.192 0.335 1.099 1.291 0.091 0.185 0.300 0.394

0.008

0.212

0.279

0.072

0.032 0.072 1.314

0.081 0.184 0.280 0.411 0.529 0.712 0.810 0.830

0.049

1.32x101 hours

0.159 0.529

0.027

125I

5.99x 101 days 1.57x 10 7 years

0.051

0.035 0.039

0.027

129I 1311

8.02 days

0.334 0.606

111in

2.80 days

192ir

7.38• 101 days

0.256 0.536 0.672

0.296 0.308 0.316 0.468 0.604 0.612

40K

1.26• 109 years

1.312

1.469

42K

1.24• 101 hours

1.996 3.521

1.524

85Kr

1.07•

0.173 0.687

0.514

0.080 0.284 0.364 0.637 0.722 0.171 0.245

years

0.030

0.023

Man-made Radioactivi~

99

Radionuclide

T1/2

[~max

176Lu

3.79• 101~years

0.589

54Mn 99Mo+99mTc

3.12• 2.75 days

0.436 0.848 1.214

22Na

9.50x 102 days

0.545

24Na

1.50x 101 hours

1.390

63Ni 237Np+233pa

1.00x 102 years 2.14x 106 years

32p 21opb 147pm 21Opo 238pu

1.43x 101 days 2.22x 101 years 9.58x 102 days 1.38x 102 days 8.77x101 years

239pu

2.41 x 104 years

l~176

3.93x 101 days

0.113 0.226

0.040 0.497 0.610

3.73x 102 days

0.979 2.407 3.029 3.541

0.512 0.622 1.050

35S

8.74x101 days

0.167

125Sb+125mTe

1.01xl03 days

0.095 0.125 0.303 0.446 0.622

l~

+l~

days

4.766 4.771 4.788

0.066 0.156 0.174 0.232 0.260 0.572

XI< 0.088 0.202 0.307 0.835 0.140 0.181 0.739 0.778 0.511 1.275 1.368 2.754

0.056

0.030 0.087 0.143 0.195 0.312 0.340

0.098

0.005

1.710 0.047 0.225 0.803

5.305 5.456 5.499 5.105 5.143 5.156

0.176 0.428 0.463 0.600 0.636

0.027

continued

l O0

Chapter 4

Table 4.9 (continuation) Radionuclide

TI/2

75Se

1.20• 102 days

113Sn+113mIn

1.15• 102 days

85Sr

6.49•

XK

~max

days

89Sr

5.06• 101 days

9~176

2.82• 101 years

99Tc 99mTc 228Th

2.14• 105 years 6.01 hours 6.99• 102 days

2~

3.04 days

2~ 232U

1.38• 103 days 6.98• years

233U

1.59• 105 years

235U

7.04• 108 years

127Xe

3.64•

133Xe 88y

5.41 days 1.07• 102 days

0.346 0.755

9Oy

2.67 days

2.284

0.121 0.136 0.265 0.280 0.401 0.255 0.392 0.514

0.010

0.140 0.084 0.132 0.216 0.135 0.167

0.018

0.024 0.013 0.015

1.492 0.546 2.284 0.294 5.340 5.423

0.071

0.763 5.263 5.320 4.824

0.058 4.783

4.218 4.365 4.400 4.556 4.599

days

0.042 0.054 0.097 0.146 0.164 0.291 0.317 0.109 0.143 0.163 0.185 0.205 O.057 0.145 0.172 0.203 0.375 0.081 0.898 1.836

0.029

0.013 0.090 0.105

0.028 0.029 0.032 0.033 0.031 0.014

Man-made Radioactivity

101

Radionuclide

TI/2

ot

~max

Y

XK

169yb

3.20• 101 days

0.050

days

0.330

0.063 0.109 0.130 0.177 0.198 1.115

65Zn

2.44•

95Zr+95Nb

6.40x101days

0.366 0.399

0.008 0.009

0.724 0.756 0.766

9 europium-152 in the 100 to 1500 keV energy range, (Fig. 4.4b) 9 barium-133 in the 30 to 400 keV energy range, (Fig. 4.4a) 9 the mixed radionuclide (241Am, l~ 57C0, 139Ce,5~Cr, ll3Sn, 85Sr, 137C8,6~

88y)

in the 60 to 1836 keV energy range (Fig. 4.4c). Compared to the above standard solutions, this mixture provides a simpler spectrum, but varies greatly in time because of difference between the half-lives of the radionuclides. Solutions are generally supplied in sealed ampoules. However, solutions with high activity concentrations are supplied in capped vials, in order to allow easy handling. For environmental survey, multigamma standard solutions are characterised by: 9 low activity concentrations in large volumes, approximating the experimental conditions for the monitoring of radioactive effluents; 9 a packaging allowing the use of the standard without opening the container, for the direct calibration of NaI(T1) and Ge(Li) detectors. The standard sources have been designed in order to allow the calibration of all the classical detectors of or, [3, e-, 7, n, X radiation (ionisation chambers, Geiger-Mtiller or proportional counters, scintillation or solid-state counters, etc.). They are classified as: alpha sources, electron sources, beta sources, gamma sources, neutron sources, X-ray sources, heat flux sources, and sources for radiation protection dose meters. Other solid sources are supplied as references and standards for biology and medicine including: iodine-125 mock standard, sources and accessories for gammacameras, and gamma reference sources for dosimeters. Alpha sources as standard sources are characterised either in terms of activity (Bq) or in terms of emission flux in 2rt sr (s-l). The radionuclide is electroplated, either on a polished stainless steel disc 25 or 30 mm in diameter and 0.5 mm thick, or polished platinum disc 22 mm in diameter and 0.1 mm thick. The contribution of the sources to the FWHM of a spectrometer is about 1 keV, the total FWHM being thus for a commercial spectrometer less than 15 keV. All these sources can be used for energy calibration of efficiency calibration for all detectors and c~ measuring devices (see Table 4.10 for the list of alpha sources).

Chapter 4

102

a) o~

i -

i~

r

L

t~

eq

oO e~

. . . . . . . . . . . .

..;,

i

...... _

L_ . . . . . . . . .

i iI ....................

t

0

I~

il

i

100

200

.......

300

keV

b)

F eq

:

i

t _

i

i~

eq

!I L i

.... _

~

~

eq

......

"'IL~

J-

i

b _

500

_

J

1500

1000

keV

..,..

t~

e~

oc

i

k,, ' i il 0

500

1000

1500

keV

Fig. 4 . 4 . G a m m a ray e n e r g y spectra. (a) B a r i u m - 1 3 3 ; (b) E u r o p i u m - 1 5 2 ;

(c) m i x t u r e s o f r a d i o n u c l i d e s .

Man-made Radioactivit3,

103

Electron sources for spectrometry as standard sources are characterised in terms of electron emission flux in 4rt sr solid angle, expressed in s-1. They are point sources (~3<4 mm) very thin and deposited on a metallised mylar film (1 mg x cm -2 thick); they are mounted on a metallic ring which provides rigidity and easy handling. The contribution of the source to the F W H M of a spectrometer is less than 1 keV, the total F W H M being thus for a semiconductor detector, less than 3 keV (for the list of the sources available see Table 4.11). Sources for calibration of beta detectors as standard sources are characterised in terms of emerging [~ emission flux in 4rt sr solid angle, expressed in s-~. Intended for the Table 4.10 Alpha sources Radionuclide

Half-life

c~ energies (MeV)

241Am

4.33x102 years

5.443 5.486

244Cm

1.81 x 101 years

5.666 5.763 5.805

21~

1.38x102 days

5.305

238pu

8.77x101 years

5.456 5.499

239pu

2.41 x 104 years

5.105 5.143 5.156

233U

1.59•

4.783 4.824

years

Table 4.11 Electron sources for spectrometry Radionuclide

Half-life

Radiation energies (MeV)

l~176

4.63• 102 days

0.062 0.084

139Ce

1.38• 102 days

0.127 0.165 0.165

137Cs+137mBa

3.02• 101 years

0.624 0.656

ll3Sn+ll3mln

1.15•

0.364 0.388

days

104

Chapter 4

Table 4.12 Sources for calibration of beta detectors Radionuclide

Half-life

Radiation energies ~max(MeV)

14C 144Ce+l~Pr

5.73x103 years

0.156

2.85x 102 days

36C1

3.01x105 years

0.185 0.238 0.318 2.996 0.709

6~

1.93x 103 days

0.318

134Cs

7.55x102 days

137Cs+ 137mBa

3,02x 101 years

22Na

9.50x 102 days

0.089 0.415 0.658 0.511 1.173 0.545

147pm

9.58x 102 days

0.225

89Sr

5.06x 101 days

1.492

9~176

2.82x 101 years

2~

1.38x103 days

0.546 2.284 0.763

calibration in efficiency of [3 detectors and counting systems, these sources are hot sealed between two thin plastic foils and gold-coated. For rigidity and ease of handling, the foils are mounted on a metallic ring. This ring can be removed if necessary so that the source can be used with or without the ring holder to calibrate all 13 detectors, including windowless 2rt or 4rt counters (see Table 4.12). Two categories of gamma standard sources are provided: 1. Sources for activity calibration: These sources enable a direct calibration of y-ray spectrometers, for radionuclides for which standards are available. Moreover, with the kits of y-ray sources, the efficiency/energy curve can be plotted; in this case, knowledge of decay scheme parameters of the radionuclides involved is needed (y branching ratio, internal conversion coefficient, etc.). 2. Sources for efficiency calibration: These y-ray emission standard sources, and the associated kits, enable a direct and accurate plot of the efficiency/energy curve of y-ray spectrometers, without use of the decay parameters of radionuclides. The multigamma standard sources enable a direct and rapid plot of the efficiency/energy curve of y-ray spectrometers, without use of the decay parameters of radionuclides (Fig. 4.4c). These two methods differ mainly by their accuracies. For calibration at high energies, a 6.13 MeV special source is proposed.

Man-made RadioactiviO'

105

Gamma-ray sources for activity calibration as standard sources are characterised in terms of activity, expressed in kBq. They can be used for the calibration of all gamma-ray detectors and spectrometers NaI(T1) or Ge(Li) (see Table 4.13 for the list of radionuclides available and their characteristics). Four types of sources are available: 1. Gamma-ray point sources: The point-source is hot sealed between two thin plastic foils (overall thickness: 24 mg x cm-2). The source is mounted in a plastic ring which provides rigidity and easy handling. 2. Gamma-ray large sources: The activity of the source is uniformly distributed on the surface of a disc 50 mm in diameter. It is hot sealed between two thin plastic foils mounted between two plastic discs (overall thickness: 460 mg x cm -2) for rigidity and easy handling. 3. Gamma-ray plastic sources: The semi-point source is deposited in the leak-proof cavity of a rigid plastic holder. 4. Gamma-ray cylindrical sources: The point source is mounted at the end of a plastic rod (diameter 9 mm). A disc can be fitted to this rod to facilitate its use in automatic samples changer. These sources are particularly suited for the calibration of welltype NaI(T1) scintillation counters. Gamma-ray sources for efficiency measurements as standard sources are characterised in terms of photon emission flux in 4re sr, expressed in s-~, for each specified gammaray. The activity of the source is indicated. When an activity standard is used to determine the efficiency of a y-ray spectrometer as a function of photon energy, certain decay scheme parameters are required (gamma branching ratio, internal conversion coefficient, etc.). In this case, the calibration uncertainty is the combination of the uncertainty on the activity of the standard and of the uncertainties on the parameters of the decay scheme. The X-ray sources have been designed to allow direct calibration efficiency/energy without knowledge of the decay schemes. For the list of radionuclides and their properties see Table 4.14. Beyond 3.5 MeV, no radionuclide is usable as a reference. The usual methods of calibration used at low energies (sets of different sources or multigamma sources) cannot be applied. Two methods are presently used for such calibrations: 1. A semi-empirical formula allowing the extrapolation of the calibration curve towards higher energies. 2. Calibration by means of high energy gamma rays from (n,y) or (p,y) reactions produced in accelerators or nuclear reactors. These methods are time consuming, expensive and often inaccurate. The 6.13 MeV reference is a composite source of 238pu and ~3C; it emits, by de-excitation of ~60, a 6.13 MeV gamma ray:

13C(~,rt)160"

~

gamma 6.13 MeV.

The spectrum contains the 6.13 MeV peak accompanied by two escape peaks (5.62 and 5.11 MeV). These three peaks are entirely separate from the 238pu gamma ray spectrum.

106

Chapter 4

Table 4.13 Gamma-ray sources for activity calibration Radionuclide

Half- life

"~energies (MeV)

241Am

4.33• years 1.05• 101 years

0.060

133Ba

l~176

4.63• 102 days

0.088

145Ce

3.25• days 2.85• 102 days

0.145

144Ce+144pr

57Co

2.72•

days

0.014 0.122 0.136

6~

1.93• 103 days

1.173 1.333

51Cr

2.77• 3.02•

days years

0.320

537Cs+137mBa 2~ 131I

4.66• 101 days 8.02 days

54Mn 22Na

3.12x 102 days 9.90• 102 days

0.279 0.080 0.284 0.364 0.637 0.722 O.835

l~176

3.93• l05 days

l~176

3.73• 102 days

85Sr 88y

6.49• days 1.07• 102 days

65Zn

2.44•

days

0.081 0.161 0.223 0.276 0.302 0.356 0.384

0.080 0.134 0.697 1.489 2.186

0.662

0.511 1.275 0.040 0.497 0.610 0.512 0.622 1.050 0.514 0.898 1.836 1.115

107

Man-made Radioactivi~

Table 4.14 Gamma-ray sources for efficiency measurements Radionuclide 241Am

Half-life

3' energies (MeV)

4.33x102 years

0.060

4.63x 10e days

0.088

139Ce

1.38x102 days

0.166

57Co

2.72x 102 days

0.014 0.122 0.136

51Cr

137Cs+137mBa

7.55x 102 days 3.02x101 years

0.320 0.662

54Mn

3.12x102 days

0.835

ll3Sn+ll3mln

1.15x102 days

85Sr

6.49x101 days

0.255 0.392 0.514

65Zn

2.44x102 days

1.115

l~

l~

The 6.13 MeV gamma-ray is emitted without D6ppler effect; the sharpness of the ray allows us to test the resolving power of Ge high energy detectors. The half-life of the source is similar to that of 238pu, i.e. about 87 years.

4.3.3 Germany A number of interesting sources is manufactured and distributed by "DuPont": 9 DuPont Nemours (Deutschland) GmbH, Postfach 401240, D-6072 Dreieich, W. Germany, Telephone: (06103) 803-0, Telex: 4-17993 NEN D, Fax: (06103) 87897; 9 E.I. DuPont de Nemours & Co. (Inc.), 331 Treble Cove Road, North Billericay, MA 01862, USA. Toll-free 800-225-1572 (Telephone: 617-482-9595) Telex: 6817017, Fax: 617-663-7315 9 DuPont Canada, Inc., P.O. Box 660, Station A, Montreal, Quebec H3C 2V1, Canada, Telephone: 514-397-2748, Telex: 05-267687, Fax: 514-397-2720. Their products include: radiopharmaceuticals, radioimmunoassay kits for medical diagnosis, radiolabelled and liquid scintillation chemicals for research, and radioactive sources used in nuclear medicine, research and industry. Some of their sources and uses are listed below: 9 63Ni: The physical and chemical properties of 63Ni uniquely suit it to applications where a source of safe localised ionisation is required. [Half-life: 96 years; Beta energy (maximum): 66 keV, (average): 17 keV]. The long half-life decay of 63Ni

Chapter 4

108

to stable 63Cuprovides a constant ionisation level, while the pure low energy beta decay minimises the need for external shielding. 9 85Kr: The 10.7-year half-life and 0.69 MeV E max beta particle make Kr-85 ideal for weight and thickness gauging in manufacturing process control for paper, plastic film and rubber sheet. X-ray sources: X-ray fluorescence analysis is a technique for elemental identification and quantification. X-ray fluorescence sources provide stable outputs for energy, direction and intensity. Unlike competing technologies, radioisotope sources do not require external power supplied. X-ray fluorescence sources are useful either for single- or multi-element analysis. Characteristic X-ray line spectra of the elements are excited in a specimen by the source X-rays. A source is selected whose X-ray energy is slightly above the X-ray energy threshold, or "absorption edge", of the element being analysed (see Table 4.15). In energy dispersive analysis, the X-rays from the sample interact with a semi-conductor detector that gives pulses directly proportional to the energy of each X-ray. The detected count rate of the characteristic X-ray pulses is proportional to the weight fraction of the element(s) in the sample. Several sources with different X-ray photon energies can be used to analyse several elements from sodium to uranium. Proper selection of source and secondary exciter targets provide optimum sensitivities. Wherever possible, calibrated sources produced by DuPont are directly calibrated against standards certified by the National Bureau of Standards (NBA) using instruments in DuPont laboratories. DuPont participates in a Measurement Assurance Program organised by the Atomic Industrial Forum and NBA. 9

Table 4.15 X-ray fluorescence sources/exciter systems Source nuclide

Half-life

Excitation mode

Photon emission and energies

Abundance Element X-rays excited usefully

Fe-55

2.7 y

Direct

Mn K X-rays; 5.9 and 6.5 keV

28%

Na-V K X-rays Zn-Ce L X-rays

Cd- 109

462.6 d

Direct

Ag K X-rays; 22 and 25 keV

102%

Ca-Mo k X-rays W-U L X-rays

Am-241

432.2 y

Direct Secondary*

Gamma rays; 59.6 keV Mo target 17.4; 19.6 keV K X-rays

36%

Sm-Tm K X-rays V-Tc K X-rays Pr-Pu L X-rays

Co-57

271.7 d

Direct

Gamma rays; 14, 122, 136 keV

10%, 86%, 11%

Ta-U K X-rays

*Secondary mode target energy selection can be made from virtually any element which can be formed into a target.

Man-made RadioactiviO,

109

Table 4.16 Calibrated beta reference sources. Individual beta reference sources calibrated with an accuracy of _+3 to 5% (at 99% confidence). Nuclide

Half-life

Nominal activity

Principal energies (Emax 13)

Bismuth-210

22 y (Lead-210 parent)

740 Bq (0.02 ~tCi)

1.16 MeV 13

Calcium-45

164 d

0.37 MBq (10 ~tCi)

0.25 MeV 13

Carbon- 14

5730 y

5550 Bq (0.15 ~Ci)

0.156 MeV [3

Caesium- 137

30 y

1480 Bq (0.04 ~tCi) 0.37 MBq (8 ~tCi)

0.52; 1.1 MeV 13 0.662 MeV 3t

Chlorine-36

3x105 y

740 Bq (0.02 ~tCi) 740 Bq (0.02 ~tCi) 0.074 MBq (2 ~tCi)

0.714 MeV [3

Cobalt-60

5.25 y

1480 Bq (0.04 ~tCi) 0.030 MBq (0.8 ~tCi)

0.31 MeV 13 1.17; 1.33 MeV y

Nickel-63

96 y

0.185 MBq (5 ~tCi)

0.066 MeV [3

Phosphorus-32

14d

0.37 MBq (10 ~Ci)

1.71 MeV [3

Promethium- 147

2.6y

3700 Bq (0.1 ~tfi) 3700 Bq (0.1 ~tCi)

0.224 MeV 13

Strontium-90 Yttrium-90

28.5 y

740 Bq (0.02 ~tCi) 740 Bq (0.02 ~tCi) 3700 Bq (0.1 ~tCi)

0.546 (2.27) MeV 13

Sulfur-35

87 d

0.37 MBq (10 ~tCi)

0.167 MeV

Technetium-99

2x 105 y

1480 Bq (0.04 ~tCi) 1480 Bq (0.04 ~Ci)

0.292 MeV [3

E a c h c a l i b r a t e d r e f e r e n c e s o u r c e is supplied with a calibration certificate listing: 9 the s o u r c e nuclide, activity and date o f calibration; 9 the radiation e m i t t e d by the source (half-life and principal radiations with abundance); 9 a d e s c r i p t i o n o f the p h y s i c a l f o r m o f the source; 9 a d e s c r i p t i o n o f the m e t h o d o f calibration; 9 the r a d i o a c t i v e impurities, if any; 9 A n analysis o f the r a n d o m and s y s t e m a t i c errors a s s o c i a t e d with the calibration measurement. T h e list o f c a l i b r a t e d b e t a r e f e r e n c e s o u r c e s is s h o w n in T a b l e 4.16, while calibrated g a m m a r e f e r e n c e s o u r c e s are s h o w n in T a b l e 4.17.

110

Chapter 4

Table 4.17 Calibrated Gamma Reference Sources Nuclide

Half-life

Nominal activity

Principal energies (Ema x [~)

Americium-241

432.2 y

0.185 MBq (5 ~tCi)

0.060 MeV y

Barium-133

10.5 y

3700 Bq (0.1 ~tCi) 0.259 MBq (7 ~tCi) 0.037 MBq (1 ~tCi)

0.080, 0.302, 0.356 MeV y (others at 0.276, 0.054, 0.161 MeV)

Cadmium- 109

462.6 d

0.037 MBq (1 ~tCi) 0.296 MBq (8 ~tCi) 0.296 MBq (8 ~tCi)

0.088 MeV y 0.023 MeV X-ray

Caesium-137

30 y

3700 Bq (0.1 ~tCi) 3700 Bq (0.1 ~tCi) 0.037 MBq (1 I.tCi) 0.259 MBq (7 ~tCi) 0.037 MBq (1 ~tCi) 0.037 MBq (10 ~tCi) 0.296 MBq (8 ~tCi)

0.662 MeV y 0.031 MeV X-ray

Chromium-51

27.7 d

0.37 MBq (10 ~tCi)

0.320 MeV y 0.0049 MeV X-ray

Cobalt-57

271.7 d

3700 Bq (0.1 ~tCi) 3700 Bq (0.1 ~tCi) 0.259 MBq (7 ~tCi) 0.037 MBq (1 laCi) 0.37 MBq (10 ~tCi)

0.122, 0.136, 0.01 MeV 7 0.006 MeV X-ray

Cobalt-60

5.27 y

3700 Bq (0.1 [aCi) 0.030 MBq (0.8 ~tCi) 0.259 MBq (7 ~tCi) 0.030 MBq (0.8 ~tCi) 0.030 MBq (0.8 ~tCi)

1.173, 1.333 MeV 7

Gadolinium- 153

242 d

3700 Bq (0.1 ~tCi)

0.97, 0.103 MeV 7 0.043 MeV X-ray

Iodine- 125

59.6 d

0.37 MBq (10 ~tCi)

0.035 MeV y 0.027 MeV X-ray

Iodine-129

1.6 x 107 y

2960 Bq (0.08 ~tCi) 2960 Bq (0.08 ~tCi)

0.039 MeV y 0.029 MeV X-ray

Iodine- 131

8.021 d

0.296 MBq (10 ~tCi)

0.364, 0.637 MeV y

Manganese-54

312.14 d

5500 Bq (0.15 ~tCi) 0.259 MBq (7 ~tCi) 0.037 MBq (l~tCi)

0.836 MeV y 0.0054 MeV X-ray

Sodium-22

2.6 y

3700 Bq (0.1 ~tCi) 0.259 MBq (7 ~tCi) 0.037 MBq (1 ~tCi)

0.511, 1.27 MeV y

Man-made Radioactivity

111

4.3.4 United Kingdom AEA Technology is the commercial division of the United Kingdom Atomic Energy Authority: Their address is: 9 AEA Technology, 220 Harwell, Didcot, Oxfordshire OX11 0RA, U.K. Telephone: (+44) 235 434212; Fax: (+44) 235 434522. Their 9 9 9 9 9 9

production line includes" Solid alpha and beta sources High purity tracer solutions Bulk dispensed radionuclides Plutonium and uranium s t a n d a r d s - certified nuclear reference materials Standard sources for non-destructive plutonium assay Californium fission fragment sources.

Some 9 9 9 9 9 9

of the special sources the company has supplied include: 36C1 and 9~ check sources for contamination-in-air monitors Very high resolution 241Am source, <10 keV FWHM 20 Bq natural uranium sources on 100 x 160 mm plates 241Am source of specified activity in epoxy resin High-intensity 238pu sources for diagnostic probes Mixed-actinide sources (23Su + 238pu + 239pu + 244Cm + 252Cf) for alpha energy calibration.

Their stock of alpha radiation sources are listed in Table 4.1 8. Table 4.18 Alpha Radiation Source Isotope(s)

Principal alpha energy (MeV)

Nominal activity (kBq)

e39pu, e41Am, 242Cm

5.157, 5.486, 5.805

0.06-0.08, 0.5-0.7, 5-8, 4-6

241Am, ea3Am, 244Cm

5.486, 5.274, 5.805

0.003-0.2, 0.08-0.9, 0.001-0.010

237Np, 241Am, 244Cm

4.788, 5.486, 5.805

0.06-0.4, 0.1-0.6, 0.5-1.4

233U, 238pu, 239pu, 244Cm, 25~

4.824,5.499, 5.157, 5.805, 6.118 0.1-0.2, 0.1-1.0, 2.0-5.0

natu, 239pu, 241Am

4.196, 4.775, 5.157, 5 . 4 8 6

0.002-0.005

239p

5.157

0.8, 0.4-5.5

24~

5.168

0.6-9.3

241Am

5.486

0.7-0.8, 0.04-66, 0.3-1.5, 0.1-2.8

244Cm

5.805

1.5-3.5

1 12

Chapter 4

The high purity tracer solutions specially formulated for environmental analysis and equilibrium studies include a wide range of radionuclides. The list of radioisotopes includes: 93mNb

2~opb

208p0

209p0

210po

223Ra

226Ra 232Th

227Ac 23~Pa

227Th 233pa

228Th 232U

229Th

23~

233U

234U

235U

236U

237U

238U

natU

235Np

237Np

236pu

238pu

239ptl

240pt1

241pu

ea2pu

241Am

243Am

242Cm

244Cm

2s~

All of them are in carrier-free solutions and sealed in glass ampoules for highest purity with certified isotopic composition and each sample individually documented. The list of plutonium and uranium standards used as certified nuclear reference materials in safeguards-related measurements is shown in Table 4.19. Another institution of interest in the U.K. is: 9 Centre for Ionising Radiation Metrology, National Physical Laboratory, Teddington, Middlesex TW 1 1 0LW, U.K. Telephone: (+44) 18 1 977 3222; Fax: (+44) 18 1 943 6 16 1, E-mail: [email protected]. NPL radioactivity standards include: 9 Gamma-ray emitting standards: 7Be, ~SF, 24Na, 42K, 43K, 465c, 47Ca, 475c, 51Cr, 54Mn' 55Fe, S6Co' 56Mn ' 57C0 ' 58C0 ' 59Fe ' 6~ ' 64Cu ' 65Zn ' 67Cu ' 67Ga ' 68Ga ' 75Se ' 82Br' 85Sr' 86Rb ' 87mSr' 88y, 95Nb ' 99M0 ' 99mTc ' 106Ru ' 109Cd ' ~ I n , 1J3In, Jl3Sn, 1231, 1241, 125i, 1255b ' 129I, 131I, 1321, 133Ba ' 134Cs ' 137Cs ' 139Ce' 141Ce ' 144Ce ' 152Eu ' 153Gd ' 1535m ' 154Eu' 155Eu' 16~ ' 169yb ' 17~ 182Ta ' 192ir' 197Hg ' 198Au ' 199Au ' 2~ ' 2~ ' 2~ ' 232U, 233pa, 237U, 237Np, 238pu, Z39Np, 241Am, 242r~ t'u, and 243Am"

9 Pure beta-ray emitting standards: ~4C,32p, 355, 89Sr ' 90Sr+90y, 99Tc ' 147pm ' and 2~ 9 Gamma-ray reference sources: 22Na, 54Mn, 56C0, 57C0, 58C0, 6~ 75Se, 88y, 109Cd ' ll3Sn, 133Ba, 137Cs, 139Ce, 152Eu and 169yb. 9 Gas standards: Tritium (3H), Radon(222Rn), 85Kr and ~33X. Standards of radioactive surface contamination: 9 beta-emitters: 3H, 14C, 147pm, 36C1, 9~176 9 alpha-emitters: 237Np, 238U, 241Am photon-emitters: 55Fe. 9 NPL secondary standard radionuclide calibrator standards: 7Be, 18F, 22Na, 42K, 465c ' 47Ca ' 475c ' 51Cr ' 54Mn ' 57C0 ' 58C0 ' 59Fe ' 6~ ' 65Zn ' 6VGa ' 755e ' 82Br, 85Kr' 85Kr, 86Rb ' 87mSr ' 88y, 99Mo ' 99Tc ' 106Ru ' m9Cd ' ~ I n , 1135n, 123I, 124I, 125I, 131I, 133Ba, 133Xe, 9

134Cs ' 137Cs ' 139Ce ' 141Ce ' 144Ce ' ~5:Eu ' 153Gd ' 153Sm ' 154Eu' 16~ ' 169yb ' 192ir' 197Hg ' 198Au ' 199-/A_u, ZOlT1' 203pb' 203Hg ' 233pa ' 237Np ' 239Np ' 241_ /-km.

9 Pure beta-emitters: 32p, 89Sr and 90y; Brachytherapy sources: 192Irwire and hairpin sources. 9 Environmental standards: 241Am, 243Am, laG, 134Cs, 137Cs, 152EH, 129I, 242pu, 9~

99Tc, 232U,mixed,

gas and natural matrix" milk powder

(137Cs& 134Cs),222Rn(gas).

Man-made Radioactivi~.

113

Table 4.19

Certified nuclear reference materials (Characterised and certified for analysis and safeguards) Application

Material

Composition, certified values

Elemental Analysis

Uranium dioxide pellets Plutonium-gallium alloy

Isotopic Analysis

Uranyl nitrate solution ( 1:1:1) Uranyl nitrate solution (1:1:1) Plutonium nitrate solution (1:1 : 1) Plutonium nitrate solution (1:1:1) Plutonium nitrate solution (6% 24~ Plutonium nitrate solution (3:3:3:1) Plutonium nitrate solution (34% 24~

(88.136_+0.006)wt% U (98.075-+0.017) wt% Pu 233U:235U (0.9991,+0.0004) 238U:235U (0.9994,+0.0006) 233U'235U (0.9991,+0.0004) 238U'235U (0.9994,+0.0006) 24~ (0.9999,+0.0006) 242pu:239pu (0.9999_+0.0010) 24~ (0.9999-+0.0006) 242pu:239pu (0.9999-+0.0010) 24~ (0.0638_+0.0007)

Burnup Analysis

U+Pu+Nd nitrate solution U+Pu+Nd nitrate solution Nd isotopic mixtures

24~ (0.9662,+0.0011) 242pu:239pu (1.0253,+0.0019) 244pu:239pu (0.3358,+0.0008) 24~ 239pu (0.54 37,+0.0003 )

99.2% U, 0.5% Pu, 0.3% Nd In preparation 67% U, 30% Pu, 3% Nd In preparation 142Nd/143Nd (0.087966,+0.000097) 144Nd/la3Nd (1.512985,+0.000670) 145Nd/143Nd (0.861148-4-0.000476) 146Nd/143Nd (0.766473,+0.000385) 148Nd/la3Nd (0.432400,+0.000337) 15~ (0.195368,+0.000190)

4.3.5 Russia Information from Russia is limited and is based on personal communications. The address below is of interest for the many radioisotopes they produce, but especially highly enriched actinide isotopes as shown in Table 4.20 (see Vesnovskii and Polynov, 1992; Vesnovskii et al., 1992; Vesnovskii et al., 1993): 9 Dr. S.P. Vesnovskii, Radiochem. Dept., Russian Federal Nuclear Center, 607200 Arzamas-16 Nizhny Novgorod Region, Russia, Fax: 831-30-54565. Electromagnetically enriched radioactive Cm, Am and Pu isotopes are available also through the following enterprise: 9 All-Union Foreign Economic Association "Techsnabexport" Staromonetniy Per., 26, 109180 Moscow, Russia, Tel.: 233-48-46, Telex: 411328 TSESU, Fax: 233-18-59.

114

Chapter 4

Table 4.20 Highly enriched actinide isotopes u-233 u-235 U-238 Pu-238 Pu-239 Pu-240 Pu-241 Pu-242 Am-241 Am-242m Am-243 Cm-243 Cm-244 Cm-245 Cm-246 Cm-247 Cm-248

99.947% 99.993% 99.997% 99.6% 99.3% 100% 93% 99.98% >99.9% 73% 99.998% 93.6% -100% 99% 80-95% 73-85% 97%

The isotopes of Cm, Am and Pu are supplied as: 9 oxides, nitrates, chlorides in glass ampoules; 9 thin layers on solid backings of all sorts. Highly enriched curium isotopes: Cm-243: 93.3-99.99%; Cm-244: 99.9%; Cm-245: 98.4-99.998%; Cm-246: 99.5-99.8%; Cm-247: 70.3-90.2%; Cm-248: 95.8-97.0, americium isotopes: Am-242m: 66.8-73.6%; Am-243: 99.2-99.94%, and plutonium isotopes: Pu-238: 99.6; Pu-239: 99.9977%; Pu-240: 99.9-100%; Pu-241: 99.699.998%; Pu-242: 97.8-99.96%, are available for scientific and applied research in physics, chemistry, geology, medicine, biology and other fields.

4.3.6 Others Many reactors and accelerators around the globe are involved in the business of radioisotope production. Most of them satisfy only local needs; many would be glad to find customers outside their region. As a matter of interest, we mention: 9 Institute of Physics & Nuclear Engineering, Bucharest, M~gurele, P.O. Box MG6, R-76900 Romania. Telephone: 401 780-59-40, Fax: 401 312-11-45, Telex: 11350. They produce 192Ir, a radioactive source used in brachiotherapy. The source in the shape of a wire (~ = 1 mm, h = 40 mm) is packaged in a stainless steel cylinder and is used for the treatment of malignant tumours. In addition, they produce sets of standard radioactive sources and solutions, whose activities are certified with an expanded uncertainty of only a few percent. The description of different sets and their characteristics are shown in Table 4.21.

0

0

~, i ,

r r~

o

0

0 r~

~

0

r r~

0 . ,...~

r

<

~ ,i~

~

8~

0

.>_ ~.

"~ = .= .~

iR

E

.=

,., ~

r~

~

,-~

~.-~

E E

E

<

cq

+1

QQ

C',I

m

c,l

m

...-

E

[-

+

,ll,

~

+1

E

VI

"-~

C'-I

r.~

+1

[.~l]

VI

Q~|

:

E

,.~

"~.~ .~ ~ ~ . ~ ; -..~ ~ . z 9

.,~

~'~= q.)

~5

Man-made Radioactivi O,

C'.I

[-,

r.~ .ill.

t.0

o~

r.~

E E

u

r,j

.-,

E E C~

Q|


r r.~

E E r,3 r,D

~

•

o

l~

o

r.~

E

EE~

E E

~E

r.,j

II

~Q

II

QQ

+1 vI

o ~

,..

#

-~

.~

,i~

_

•

,,,,i.

x

%

r

e... c~

r.~ "I., ~

._o

0

. ,,.i4

0 r.~

r.~

115

116

Chapter 4

REFERENCES Even, G.W., Tracer techniques in hydrology. Appl. Radiation Isotope 34, 1 (1983) 451-475. Holmshaw, R. (ed.), Physics of Industrial Radiology. Heywood Books, London, 1966, 498 pp. International Atomic Energy Agency, Isotopes in Everyday Life. IAEA, Vienna, 1993. International Commission on Radiological Protection. Recommendations of the International Commission on Radiological Protection (adopted 17 Jan, 1977). ICRP Publication 26. Annals of the ICRP, Sowby, F.D. (ed.), Pergamon Press, Oxford, 1977. Kazantzis, G., In: Friberg, L., Nordberg, G.F. and Vouk, V.B. (eds.), Handbook of the Toxicology of Metals. Elsevier, Amsterdam, 1986, Ch. 22, pp. 549-567. Pennal, D.J., Underwood, R., Costa, D.C. and Ell, P.J., Thallium Myocardial Perfusion Tomography in Clinical Cardiology. Springer-Verlag, London, 1992. Radiological Research and Radiotherapy, Vols. I and II. Proc. Int. Syrup. on Radiological Research needed for the improvement of Radiotherapy. Vienna 22-26 Nov. 1976. IAEA Vienna, 1977. Stein, S. and Aaseth, J., Thallium-201 as an agent for myocardial imaging studies. Analyst 120 (1995) 779. The Application of Radioactive Tracers in the Water Industry, in Four Essay Reviews on Applications of Radiation Measurement in the Water Industry 1984, HMSO, in this series. Vesnovskii, S.P., Polynov, V.N., Nikitin, E.A. and Vjachin, U.N., Quality and availability of actinide isotopes from All-Russian Scientific Research Institute of Experimental Physics in Arzamas-16. Nucl. Instrum. Meth. Phys. Res. A334 (1993) 37. Vesnovskii, S.P., Polynov, V.N. and Danilin, L.D., Highly enriched isotope sample of uranium and transuranium elements for scientific investigation. Nucl. Instrum. Meth. Phys. Res. A312 (1992) 1. Vesnovskii, S.P. and Polynov, V.N., Highly enriched isotopes of uranium and transuranium elements for scientific investigation. Nucl. Instrum. Meth. Phys. Res. A312 (1992) 9. Witsenboer, A.J., de Goeij, J.J.M. and Reiffers, S., Production of '23I via proton irradiation of 99.8% enriched '"4Xe. J. Labelled Compounds Radiopharm. 23 (1986) 1284.