Measurement of Fission Product Yields at the National Synchrotron Light Source II*

The amount of a specific isotope produced in the fission of a heavy nucleus, the Fission Yield (FY), is a fundamental quantity that impacts several applications like reactor physics, nuclear forensics, and nuclear waste; precise knowledge of FYs can also advance the understanding of the fission process itself, as it is one of the observables used to test theoretical models. We distinguish between the independent FY, amount produced directly in fission, and cumulative FY – which include the contribution of the nuclides decaying into the fission product of interest. The most precise determination of cumulative FYs of long-lived fission products to date was performed using mass spectroscopy (AMS) by Maeck et al. in the 1970s at Idaho National Laboratory with uncertainties as low as 1%. The results from Maeck are the foundation of the current recommended FY distributions published in the ENDF/B  data library. However, while yields as low as 0.1% were measured, some refractory elements could not be accessed with AMS.

We present progress on an innovative program that would take advantage of the bright X-ray beams available at the National Synchrotron Light Source II (Brookhaven National Laboratory) to measure high-precision cumulative charge yields of long-lived and stable fission products from neutron-induced fission of actinides using X-ray Fluorescence.  In this first phase of the program, we are developing the workflow and confirming the sensitivity of this method measuring a series of foils irradiated at the University of Massachusetts at Lowell Research Reactor. Various elements transmuted via neutron-capture reactions will beta decay, changing the proton number in the reaction products. The fraction of the elements transmuted in these irradiations, assessed using XRF, will demonstrate the feasibility of this method.