Specific activity nuclear reactors

This can result in a radioactive product from the A(n, t)A reaction where A is the stable element, n is a thermal neutron, A is the radioactive product of one atomic mass unit greater than A, and y is the prompt gamma ray resulting from the reaction. A is usually a beta and/or gamma emitter of reasonably long half-life. Where access to a nuclear reactor has been convenient, thermal neutron activation analysis has proven to be an extremely valuable nondestructive analytical tool and in many cases, the only method for performing specific analyses at high sensitivities... 

The nuclear power industry (270 nuclear reactors in 25 countries in mid-1982) now has a capacity of 200 GWe, which corresponds to an approximate annual plutonium production of 50 tonnes. The amount of plutonium accumulated from the industry is estimated to be 250 tonnes. The specific activity is 5.3X1011 Bq/g Pu for fresh spent fuel, mostly coning from 2ltlPu (6, 10). It is predicted that by the year 2000, the accumulated plutonium will amount to 2400 tonnes (6). 

Although the transient test was orders of magnitude below a nuclear weapon in regard to energy release and temperature achieved, the debris showed many similarities to fallout. These included not only the size and appearance of the particles but also the correlation properties of various radionuclides. Dissimilarities in the correlations and the variation of specific activity with particle type confirm expectations of the importance of escape processes to the formation mechanisms for this type of debris. This study shows that data-correlation techniques developed for fallout characterization are also useful in studying reactor debris. 

CsI8F reacts at a much higher rate than K18 F47 and has been produced routinely by irradiation of 6Li2C03 in a flux of neutrons in a nuclear reactor for 3 h48. High-specific-activity [I8F]fluoronicotine has been needed for use in humans because of the toxicity of nicotine and to minimize the non-specific binding in receptor binding studies. 

Another approach is whole-manuscript neutron activation analysis (NAA) in a nuclear reactor, followed by gamma-ray analysis and autoradiography (4). Gamma-ray analysis permits identification of the elements contained in the manuscript, and autoradiographic analysis indicates the specific locations of these elements. A similar approach applied to art objects of historical interest is energy-dispersive X-ray fluorescence (XRF) analysis, which permits nondestructive semiquantitative elemental analysis (5). 

The discovery of Pu has been described in detail by Seaborg in his Plutonium Story (chapter 1 of the book The Transuranium Elements 1958). First, the separation of Pu from Th caused some difficulties, because both elements were in the oxidation state 4-4. After oxidation of Pu(IV) by persulfate to Pu(VI), separation became possible. Pu is produced in appreciable amounts in nuclear reactors (section 14.1), but it has not immediately been detected, due to its low specific activity caused by its long half-life. After the discovery of Pu, plutonium gained great practical importance, because of the high fission cross section of Pu by thermal neutrons. Very small amounts of Pu are present in uranium ores, due to (n, y) reaction of neutrons from cosmic radiation with The ratio Pu/ U is of the order of 10 In 1971, the longest-lived isotope of plutonium, Pu (ri/2 = 8.00 lO y) was found by Hoffman in the Ce-rich rare-earth mineral bastnaesite, in concentrations of the order of 10 gAg-... 

In the (n, y) reaction with natural arsenic (100% As) in a nuclear reactor with a flux of 10 ncm s, samples of As with specific activity of 920mCig are obtained only. Cyclotron arsenic isotopes As are utilized in short-term biological experiments, As for medium-term experiments. 

Radioactive nuclides are produced principally in the nuclear reactor as the result of (n, y), (n, p) and (n, d) reactions (p. 23). When a high specific activity is required an (n, y) preparative reaction is unsuitable because the product is necessarily diluted by the parent isotope, from which separation is always difficult and generally impossible, as in the Na(n, y) Na conversion, is conveniently made by irradiating LiOH in a reactor ... 

With the commercial development of nuclear reactors, the actinides have become important industrial elements. A major concern of the nuclear industry is the biological hazard associated with nuclear fuels and their wastes 2). In addition to their chemical toxicity, the high specific activity of alpha emission exhibited by the common isotopes of the transuranium elements make these elements potent carcinogens (3, b 9 5, 7). Unlike organic... 

Among the long-lived isotopc.s, Tc is the only one which is obtained in weighable amounts. It is formed in high yield by the fission of U, and quantities of the order of kilograms can be isolated from nuclear reactor fission product waste solutions. Because of the relatively low specific activity of 17 pCi/mg (629 kBq/mg) and the weak /l -radiation ( rnax=0-29 MeV), the laboratory handling of Tc needs no special radiation protection. 

Tc is available through the /l -decay of Mo (Fig. 2.1.B), which can be obtained by irradiation of natural molybdenum or enriched Mo with thermal neutrons in a nuclear reactor. The cross section of the reaction Mo(nih,v) Mo is 0.13 barn [1.5], Molybdenum trioxide, ammonium molybdate or molybdenum metal are used as targets. This so-called (n,7)-molybdenum-99 is obtained in high nuclidic purity. However, its specific activity amounts to only a few Ci per gram. In contrast, Mo with a specific activity of more than in Ci (3.7 10 MBq) per gram is obtainable by fission of with thermal neutrons in a fission yield of 6.1 atom % [16]. Natural or -enriched uranium, in the form of metal, uranium-aluminum alloys or uranium dioxide, is used for the fission. The isolation of Mo requires many separation steps, particularly for the separation of other fission products and transuranium elements that arc also produced. 

Some examples of applications of nuclear activation analytical techniques to elemental determinations in a variety of materials are presented in Table 2.10. The specific contents of some of these and other publications may be briefly highlighted. Cunningham and Stroube Jr. (1987) provide a nice coverage of the application of an instrumental neutron activation analysis procedure to analysis of food, describing the capabilities of INAA for the multielement analysis of foods as carried out for many years, and also currently, by analysts of the US Food and Drug Administration stationed at the NIST Nuclear reactor facility. Salbu and Steinnes (1992) touch upon applications of nuclear analytical techniques in environmental research, and Norman and Iyengar... 

Carbon-14 collection. Carbon-14 is formed in nature by cosmic-ray interactions. It is in all carbon-containing compounds that are in equilibrium with C in air at a specific activity of 0.23 Bq g carbon. Concentration measurements in carbon-containing compounds that are no longer at equilibrium with air, such as dead trees, are used to determine their age —the time period since the end of equilibrium with airborne carbon—in terms of the fractional radioactive decay. Huctuations of cosmic-ray production of C in air over the centuries must be considered in this determination (NCRP 1985a). Carbon-14 is also produced at low rates in nuclear reactors, mostly by the (n,p) reaction with and the (n,o ) reaction with O. 

More confident attribution usually is possible when radionuclides in a sample can have only limited origin from, say, atmospheric fallout and one or two nuclear facilities. For tritium, I, or uranium in the environment, for example, the specific activity (radioisotope/stable isotope ratio) can indicate the origin. Certain activation products can be attributed to specific nuclear medicine or reactor facilities. 

In medicine, 1-131 is supplied in capsules or liquid of a specific activity designed to be sw-allowed by patients. As a product of nuclear fission, it is a dark purple gas that can be inhaled, or absorbed through the skin. 1-131 in fallout from nuclear weapons or reactor accidents can occur in particle form, which can be ingested in food or water. 

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