Molybdenum nuclides

A large number of nuclides have been synthesized on Earth. For instance, technetium was prepared (as technetium-97) for the first time on Earth in 1937 by the reaction between molybdenum and deuterium nuclei ... 

Among the long-lived isotopes of technetium, only Tc can be obtained in weigh-able amounts. It may be produced by either neutron irradiation of highly purified molybdenum or neutron-induced fission of uraniimi-235. The nuclides Tc and Tc are exclusively produced in traces by nuclear reations. Because of the high fission yield of more than 6%, appreciable quantities of technetimn-99 are isolated from uranium fission product mixtures. Nuclear reactors with a power of 100 MW produce about 2.5 g of Tc per day . 

Given a method of preparing Mo organometallic compounds, the p decay transformation of Mo to Tc could be studied. The decay of Mo to Tc yields a nuclide with much lower recoil energy than that formed in the molybdenum (n, y ) process. However, this decay produces a cascade of Auger electrons see Auger Spectroscopy) which can cause bond disruption. These studies are difficult, because the technetium-99m product is produced at radiochemical tracer levels. Macroscopic quantities of products are not available for spectroscopic characterization. 

Similarly, the irradiation of molybdenum with neutrons gives Mo which decays to the metastable y-ray emitting nuclide Tc. This is of great... 

Example Consider the spontaneous fission of americium-244. Two of the daughter nuclides formed are iodine-134 and molybdenum-107. The reaction is ... 

Molybdenum-105 atoms undergo four beta emissions before they reach a stable nuclide. What is the final product ... 

Fig. 5.1.A A modified section of the nuclide churt of some technetium isotopes and isolopes of rullie-niuni and molybdenum. The stable isotopes are indicated by tlie hatched sejuares.

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. 

For technetium, Z = 43, the valley of jS-stability has a minimum in the neighborhood of N = 55 and thus, for Z = 43, /4-values around 97 and 99 are most likely to be stable (recall that odd-odd nuclei are less stable than odd-even). If one considers all the isobars between A = 95 and 102 one finds that for each mass number in this range there is already at least one stable nuclide for the elements with Z = 42 (molybdenum) and Z = 44 (ruthenium). Since adjacent isobars cannot both be stable, this excludes the possibility of... 

There are 365 different nuclides in nature. Of these, 55 are radionuclides. In addition, there are hundreds of radionuclides which have been artificially manufactured, mainly by smashing nuclei together at very high speed in giant devices called particle accelerators. For example, in 1937, technetium (Tc) was made by firing deuterium atoms at molybdenum (Mo) atoms ... 

Nuclide chart showing stable molybdenum isotopes and radioactive products from deuteron bombardments... 

The production of Mo is of paramount importance to nuclear medicine. Molybdenum-99 is not directly used, but serves as the parent radionuclide for the daughter Tc, now used diagnostically in dozens of radiopharmaceuticals. Iodine-131 is widely used to treat thyroid cancer and hyperactive thyroid conditions. Production of both of these nuclides is discussed in some detail in O Sect. 38.8. Xenon-133 is used for studies of pulmonary ventilation and sometimes for cerebral blood perfusion. 

Probably the most comprehensive published assay of DU used in armor pen-etrators was reported on the basis of analysis of an unfired CHARM-3 penetrator (Trueman et al. 2004). A sample from the penetrator was dissolved in 9 M HCl, spiked with U as a yield monitor, and the uranium was separated from impurities on an ion-exchange resin. The isotopic composition of uranium was determined by mass spectrometric techniques. Actinides ( - Am and Np) were determined in the uranium-free solution by gamma spectrometry and 239+24opy and Pu were measured by alpha spectrometry and their presence was confirmed by ICPMS. Technetium-99 was determined by ICPMS when rhenium was used as a carrier and interferences from iron were eliminated by precipitating with ammonia while ruthenium and molybdenum were removed by separation on a chromatographic resin. The content of these radioactive nuclides is summarized in Table 2.7. 

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