Problems of Synthetic Actinide Elements

The Synthetic Actinide Eiements—From Discovery to Manufocture, Glemt T. Seaborg (VSAEC) 

The first synthetic actinide element, neptunium, was discovered in 1040. The last element of the actinide series, lawrencium, was created for the first time in 1061. These and the nine other intervening elements have added a new dimension to science, technology, industry, medicine, and politics in an e aordinarily short period of time. Each synthetic actinide element from atomic number 03 to atomic number 98 (with the exception of berkelium, atomic number 07) can now be manufactured in essentially any desired quantity, a truly remarkable achievement. The high points of the history of the actinide elements are traced, production methods are described, and a forecast is given of the manufacturing levels to be expected during the next decade. An analysis is presented of the current and near-term implications the various isotopes of the actinide elements. 

Critical Masses of Fissile Transplutonium Isotopes, H. K. Clark (duPont-SRL) 

Although the nuclides Pu, Am, Am, m, and Cf are not fissile, and hence cannot be made critical in a well-moderated system, they are necessarily accompanied by other nuclides that are fissile. Because the fission cross sections of these other nuclides in some cases are very large, mixtures containing them can become critical when moderated, even though their concentrations are small. Care must therefore be taken when processing the nonflsslle nuclides in a moderating medium to maintain the amounts or concentrations of fissile nuclides below subcritical limits. 

Critical masses were calculated for the fissile nuclides Am, Cm, Cm, Cm, , and Cf as a function of the concentration of the nuclide in water-reflected metal-water mixtures. The cross sections used in these calculations were those currently in use at the Savannah River Laboratory. Values of v were calculated for Am and Cm from the formula of Gordeeva and Smirenkln, which is said to be valid for N 152, where N = A - 2. For Cf, the formula is not valid. CoiMari-son of V for spontaneous fission of Pu, Pu, Cm, m, and f with v for thermal fission of Pu, Pu, em, lm, and f shows ah average difference of about 0.7. On this basis, v for Cfwas taken to be 3.78 + 

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