Preparation of uranium-223 with low uranium-232 content

Thorium dioxide, previously freed of uranium and protactinium contamination by means of ion-exchange, was irradiated for 70.5 and 140 hr respectively in the core and graphite thermal column positions of the KUR (Kyoto University Reactor). After being cooled for more than 1 1/2 yr, the 233U produced was chemically purified by ion exchange, and the resulting 233U specimens were electro-deposited on a stainless steel plate for submission to α-spectrometric measurement with a silicon surface barrier detector. From the α-spectra thus obtained, the 232U to 233U atomic ratios of the specimens were evaluated and compared with the calculated values. This revealed that the rate of formation of 232U depended largely on the 232Th(n,2n)231Th reaction by fast neutrons, and consequently, on the neutron energy distribution prevailing at the position of irradiation. The purest 233U sample obtained from the thorium target, irradiated with pure thermal neutrons in the graphite thermal column, yielded a 232U to 233U atomic ratio of 3.02x10-9, which corresponded to 6.62x10-6 in α-activity ratio. (auth.)