Abstract
Background: An assessment done under the auspices of the Organization for Economic Co-operation and Developement Nuclear Energy Agency (OECD-NEA) in 2007 suggested that the ß decays of many abundantly produced fission products in nuclear reactors may be incomplete. In this assessment, the fission product Nb98 was assigned the highest priority for study by total absorption spectroscopy due to its large cumulative fission branching fraction and because the ß-decay data from several experiments are discrepant. Purpose: To obtain the complete ß-decay feeding pattern of Nb98 and determine the impact on the average ? energy per Nb98ß decay and ?¯e emission calculations. The complete 98Nb ß-decay feeding pattern includes ground-state to ground-state ß feeding and direct ß feeding to the 0+ first-excited state (both have no associated ? rays), and the ground-state to excited-state ß transitions followed by ? transitions to the ground state of the daughter nucleus, Mo98. Method: The complete ß-decay intensities of Nb98 were measured with the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory (ORNL). The Nb98 was produced by the ß decay of mass 98 fission fragments at ORNL's On-Line Test Facility (OLTF) using proton-induced fission of U238. Results: We find that changes to the current ENSDF assessment of Nb98ß-decay intensity are required. We report improved uncertainties for the ß-decay feeding values and report new ß feedings to high-energy levels in Mo98. Conclusions: A more complete Nb98ß-feeding pattern with improved accuracy and precision is offered. The impacts of the measured changes to the Nb98ß-feeding pattern on both reactor decay heat calculations and predicted detection rates of reactor ?¯e are presented. The Modular Total Absorption Spectrometer measurements of Nb98 demonstrate the importance of reexamining and remeasuring complex ß-decaying fission products with total absorption spectroscopy, including nuclei very near ß stability.
| Original language | English |
|---|---|
| Article number | 064301 |
| Journal | Physical Review C |
| Volume | 105 |
| Issue number | 6 |
| DOIs | |
| State | Published - Jun 2022 |
Funding
We would like to thank the ORNL Tandem operations staff for providing the excellent quality proton beams necessary for this work. This research was also sponsored by the Office of Nuclear Physics, U.S. Department of Energy, under Contracts No. DE-AC05-00OR22725 (ORNL), No. DE-FG02-96ER40983 (UTK), No. DE-FG02-96ER40978 (LSU), No. DE-FG02-96ER41006 (MSU), and No. DE-SC0016988 (TTU), and supported by Grant No. UMO-2016/23/B/ST2/03559 from the Polish National Centre for Science. This manuscript has been partially supported by Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy and managed by UT-Battelle, LLC. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S.Government purposes.