PNNL

Abstract

Two well-characterized targets of high-purity (99.84+/-0.03\%) 235U-oxide and a neutron dosimetry package were exposed to a pulsed neutron irradiation using the Godiva critical assembly at the National Criticality Experiments Research Center. Following irradiation, the fissioned targets were counted with a broad-energy germanium detector. Estimates of the total fissions for each target were made using measurements of well known fission products. The total fission values were then used to measure the fission yields of 21 fission products. Mean values of seventeen of the measured fission products fell within the 95\% confidence level of the Evaluated Nuclear Data Files VII.1/b (ENDF/B-VII.1) using the larger of the two uncertainties: 84gBr, 89Rb, 91Sr, 93Y, 97Zr, 101Mo, 105Ru, 128Sn, 129Sb, 130gSb, 131Sb, 131mTe, 133I, 135I, 141Ba, 142Ba, and 142La. Seven isotopes were measured to better precision than is listed in the ENDF/B-VII.1 database: 89Rb, 93Y, 128Sn, 129Sb, 130gSb, 131mTe, and 133I. Four of the measured isotopes were found to be statistically different from the ENDF/B-VII.1 database: 94Y, 134Te, 134I, and 138Xe. Two of the isotopic analyses conducted in this paper fit the parent and daughter data simultaneously. The parent-daughter pairs measured in this way were the 134Te/I and 142Ba/La pairs. The fission yield results obtained in this way are unique, especially for 134I, because the parent and daughter half-lives are so close. Given the limited number of direct measurements of the 134Te/I pair from fast neutron induced fission and the seemingly high estimate for 134Te from previous work, it is possible that the current published value is more accurate; however, additional measurements of this pair are needed to validate this assertion.