Radionuclides tritium

Decay products of the principal radionuclides used in tracer technology (see Table 1) are not themselves radioactive. Therefore, the primary decomposition events of isotopes in molecules labeled with only one radionuclide / molecule result in unlabeled impurities at a rate proportional to the half-life of the isotope. Eor and H, impurities arising from the decay process are in relatively small amounts. Eor the shorter half-life isotopes the relative amounts of these impurities caused by primary decomposition are larger, but usually not problematic because they are not radioactive and do not interfere with the application of the tracer compounds. Eor multilabeled tritiated compounds the rate of accumulation of labeled impurities owing to tritium decay can be significant. This increases with the number of radioactive atoms per molecule. 

The radioactive products of the Sedan detonation were present in the fireball and mixed into the mass of earth moved by the detonation. As the fireball cooled, condensation occurred, and radioactivity in various forms was scavenged by earth materials entering the cloud. Apparently a large fraction of the residual tritium from the explosive was present in the cloud as tritiated steam. This tritiated water was entrained by the ejecta as it fell onto the surrounding land surface, and the resulting postshot substratum thus contained a most significant and mobile tracer. Other radionuclides scavenged by the ejected earth mass constitute another type of tracer for Sedan ejecta. 

Field study of Sedan ejecta began in 1965 with the major interest being the fate of residual tritium in the ecological system that has evolved in the Sedan postshot environment. Biological and physical aspects of the movement of radionuclides in this natural laboratory were therefore embraced in the scope of this research. Some of the results of these radiobiological and radioecological studies are reported elsewhere (5, 6, 7,8). This study is concerned with the movement of radionuclides which were deposited in the bulk and missile ejecta in the vicinity of the crater. 

The distribution of radionuclides in Sedan crater ejecta has been determined on a vertical and horizontal basis at selected sites in the area covered by ejecta. The present distribution of residual tritium represents a highly modified pattern caused by rainfall leaching. Maximum tritium concentrations are found at essentially the same depth in a transect of the ejecta field where the ejecta depth is decreasing. The source of tritium in the Sedan crater ejecta is identified as the missile ejecta layer which had greater exposure to detonation products than bulk ejecta. 

P xcept for tritium, carbon-14, and the long lived rare gases, the radio-active atoms produced by a nuclear detonation are accounted for completely within a population of radioactive particles. The nature of the particle population and the manner in which the individual radionuclides are distributed within it will vary with the conditions under which the detonation occurred. Characterization of the radioactive particle population requires ... 

The radionuclides commercially available and most commonly used for a number of the foregoing applications include anhmony-125 banum-133, 207 bismuth-207 bromine-82 cadmium-109, 115 m calcium-45 carbon-14 cerium-141 cesium-134, 137 chlorine-36 chromium-51 cobalt-57, 58, 60 copper-64 gadolimum-153 germanium-68 gold-195. 198 hydrogen-3 (tritium) indium-111, 114 m iodine-125, 129, 131 iron-55, 59 krypton-85 manganese-54 mercury-203 molvbdenum-99 nickel-63 phosphorus-32. 33 potassium-42 promethium-147 rubidium-86 ruthenium-103 samarium-151 scandium-46 selenium-75 silver-110 m sodium-22, strontium-85 sulfur-35 technetium-99 thallium-204 thulium-171 tin-113, 119 m, 121 m. titamum-44 ytterbium-169, and zinc-65. 

Note also that because radionuclides, in general, have different half-lives, the number of nuclei per curie will differ from one species to another. For example, let us calculate how many nuclei are in 1 MBq ( 27 xCi) of tritium (ti/2 = 12.33 y). We know that... 

In other words, 1 MBq of tritium contains about 3 ng of tritium. Thus, an important feature of radionuclides becomes apparent—we routinely work with extremely small quantities of material. Pure samples of radioisotopes are called carrier free. Unless a radionuclide is in a carrier-free state, it is mixed homogeneously with the stable nuclides of the same element. It is, therefore, desirable to have a simple expression to show the relative abundances of the radioisotope and the stable isotopes. This specification is readily accomplished by using the concept of specific activity, which refers to the amount of radioactivity per given mass or other similar units of the total sample. The SI unit of specific activity is Bq/kg. Specific activity can also be expressed in terms of the disintegration rate (Bq or dpm), or... 

In many situations, the experimenter will prefer to buy labeled compounds from commercial suppliers rather than attempt to synthesize them. The radiochemical purity of such purchased compounds cannot be assumed. Radiation-induced selfdecomposition (radiolysis) can result in the formation of a variety of labeled degradation products, which must be removed before experimental use of the compounds. The extent of radiolysis depends on the nature of the labeled compound, how long it has been stored, and the manner of storage. Radiolysis is most significant with low-energy (3 emitters (especially tritium) since the decay energy is dissipated almost entirely with the compound itself. Furthermore, impurities involving other radionuclides may be present. 

The National Bureau of Standards [57] has issued standard reference materials for a-emitting radionuclides in soils. These include 60cobalt, 90strontium, 90yttrium, tritium, and 106ruthenium. 

Tritium and Other Radionuclide Labeled Organic Compounds Incorporated in Genetic Material (1979)... 

Results of several radiochemical studies at the experimental study area we installed at Maxey Flats have already been described in detail elsewhere (8-10). The areal distribution of radionuclides in the surface soil throughout the site has been mapped. Groundwater flow patterns near the experimental study area have also been mapped using tritium as a groundwater tracer. 

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