Summary. During the past year the work carried out in this program has included experiments on the x-ray output produced by the separated fission product beta sources, the interpretation of such experiments for the effective design of high level secondary x-ray sources, and the design and testing of prototype sources of secondary radiation for specific industrial applications. In this report results of work carried out during the past fours months are reported: (1) analysis of beta-excited x-rays; (2) performance of Kr85 prototype x-ray source; and (3) design of high level Pm147 x-ray sources.

From the point of view of predicting melting behavior of fuel elements containing fission products after 50 percent burn-up, the fuel can be considered to consist of 2000 moles Th, 150 moles U, 55 moles of rate earth metal, 31 moles of Zr, 25 moles of Mo, 20 moles of Rh-Ru-Tc, and 15 moles of alkaline earth metal. All other fission products are present in too small amounts to have any important effect upon the melting point or will have vaporized. However, the presence of alkali metal vapor should be considered.