Absolute Integral Fission Product Chain Yield Measurements at NCERC*

Fission product chain yields were historically determined by chemical separation and beta counting of fissile samples irradiated in carefully controlled fission chamber experiments. These measurements provided the means to extract the absolute fission product yields (yield per fission, or Y_i/f for the i_th  fission product) that are included in the international nuclear data libraries, and ultimately used to model and characterize multiplying systems. However, re-evaluations conducted in the late 2010s for neutron-induced fission of ²³⁵U and ²³⁹Pu highlighted disagreement between several important measurements used in the data library evaluations.

In this presentation we will highlight recent activities to address discrepancies and data gaps using energy-integral measurements for ²³⁵U and ²³⁹Pu. This work relies on the historical combination of fission chambers and radiochemical analyses of fissile samples irradiated on the critical assemblies at the National Criticality Experiments Research Center (NCERC) at the Nevada National Security Site. Details will be provided on the design and performance of the fission chambers, along with the results from irradiations on the Flattop and Godiva critical assemblies. We will conclude with an outline of our plans to complete the work over the next several years.