Deciphering $^{98}\mathrm{Nb}$ $\ensuremath{\beta}$ decay with the Modular Total Absorption Spectrometer at ORNL

Deciphering ${}^{98}{Nb}$ $β$ decay with the Modular Total Absorption Spectrometer at ORNL

B. C. Rasco, K. P. Rykaczewski, A. Fijałkowska, M. Karny, M. Wolińska-Cichocka, R. K. Grzywacz, D. W. Stracener, E. F. Zganjar, J. C. Batchelder, J. C. Blackmon, N. T. Brewer, M. P. Cooper, K. C. Goetz, J. W. Johnson, T. King, A. Laminack, J. T. Matta, K. Miernik, M. Madurga, D. Miller, M. M. Rajabali, T. Ruland, P. Shuai, M. Stepaniuk, and J. Winger

Phys. Rev. C 105, 064301 – Published 3 June 2022

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 $β$ decays of many abundantly produced fission products in nuclear reactors may be incomplete. In this assessment, the fission product ${}^{98}{Nb}$ was assigned the highest priority for study by total absorption spectroscopy due to its large cumulative fission branching fraction and because the $β$ -decay data from several experiments are discrepant.

Purpose: To obtain the complete $β$ -decay feeding pattern of ${}^{98}{Nb}$ and determine the impact on the average $γ$ energy per ${}^{98}{Nb} β$ decay and ${\bar{ν}}_{e}$ emission calculations. The complete $^{98} Nb$ $β$ -decay feeding pattern includes ground-state to ground-state $β$ feeding and direct $β$ feeding to the $0^{+}$ first-excited state (both have no associated $γ$ rays), and the ground-state to excited-state $β$ transitions followed by $γ$ transitions to the ground state of the daughter nucleus, ${}^{98}{Mo}$ .

Method: The complete $β$ -decay intensities of ${}^{98}{Nb}$ were measured with the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory (ORNL). The ${}^{98}{Nb}$ was produced by the $β$ decay of mass 98 fission fragments at ORNL's On-Line Test Facility (OLTF) using proton-induced fission of ${}^{238}U$ .

Results: We find that changes to the current ENSDF assessment of ${}^{98}{Nb} β$ -decay intensity are required. We report improved uncertainties for the $β$ -decay feeding values and report new $β$ feedings to high-energy levels in ${}^{98}{Mo}$ .

Conclusions: A more complete ${}^{98}{Nb} β$ -feeding pattern with improved accuracy and precision is offered. The impacts of the measured changes to the ${}^{98}{Nb} β$ -feeding pattern on both reactor decay heat calculations and predicted detection rates of reactor ${\bar{ν}}_{e}$ are presented. The Modular Total Absorption Spectrometer measurements of ${}^{98}{Nb}$ demonstrate the importance of reexamining and remeasuring complex $β$ -decaying fission products with total absorption spectroscopy, including nuclei very near $β$ stability.

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Received 2 February 2022
Accepted 2 May 2022

DOI:https://doi.org/10.1103/PhysRevC.105.064301

Physics Subject Headings (PhySH)

Beta decay Energy levels Nuclear reactors Nuclear structure & decays

90 ≤ A ≤ 149

Nuclear Physics

Authors & Affiliations

B. C. Rasco^1,*, K. P. Rykaczewski¹, A. Fijałkowska^2,3, M. Karny^2,4, M. Wolińska-Cichocka^5,1,4, R. K. Grzywacz^3,1,4, D. W. Stracener¹, E. F. Zganjar⁶, J. C. Batchelder^7,4, J. C. Blackmon⁶, N. T. Brewer^4,1,3, M. P. Cooper³, K. C. Goetz^8,3, J. W. Johnson^1,†, T. King¹, A. Laminack¹, J. T. Matta¹, K. Miernik², M. Madurga³, D. Miller^3,‡, M. M. Rajabali⁹, T. Ruland⁶, P. Shuai^1,3,4,10, M. Stepaniuk², and J. Winger¹¹

¹Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
²Faculty of Physics, University of Warsaw, Pasteura 5, PL-02-093 Warszawa, Poland
³Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37966, USA
⁴JINPA, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁵Heavy Ion Laboratory, University of Warsaw, PL-02-093 Warszawa, Poland
⁶Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
⁷Department of Nuclear Engineering, University of California, Berkeley, Berkeley, California 94720, USA
⁸CIRE Bredesen Center, University of Tennessee, Knoxville, Tennessee 37966, USA
⁹Physics Department, Tennessee Technological University, Cookeville, Tennessee 38505, USA
¹⁰Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
¹¹Department of Physics and Astronomy, University of Mississippi, Starkville, Mississippi 39762, USA

^*rascobc@ornl.gov
^†Deceased.
^‡Present Address: MKS Instruments, Inc., Rochester, NY 14623, USA.

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Vol. 105, Iss. 6 — June 2022

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Physical Review C

covering nuclear physics

Deciphering ${}^{98}{Nb}$ $β$ decay with the Modular Total Absorption Spectrometer at ORNL

Phys. Rev. C 105, 064301 – Published 3 June 2022

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Physical Review C

covering nuclear physics

Deciphering Nb98 β decay with the Modular Total Absorption Spectrometer at ORNL

Phys. Rev. C 105, 064301 – Published 3 June 2022

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Deciphering ${}^{98}{Nb}$ $β$ decay with the Modular Total Absorption Spectrometer at ORNL