Improved Cumulative Fission Yield Measurements with Fission Spectrum Neutrons on 235U

Two isotopically-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 with half-lives between 636 and 119,700 seconds. 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 likely that the value in this paper is more accurate; however, additional measurements of this pair are needed to validate this assertion.

Duke Scholars

Author Anton P. Tonchev Physics