Decays of the Three Top Contributors to the Reactor ${\overline{\ensuremath{\nu}}}_{e}$ High-Energy Spectrum, $^{92}\mathrm{Rb}$, $^{96\mathrm{gs}}\mathrm{Y}$, and $^{142}\mathrm{Cs}$, Studied with Total Absorption Spectroscopy

Decays of the Three Top Contributors to the Reactor ${\bar{ν}}_{e}$ High-Energy Spectrum, ${}^{92}{Rb}$ , ${}^{96 gs}Y$ , and ${}^{142}{Cs}$ , Studied with Total Absorption Spectroscopy

B. C. Rasco, M. Wolińska-Cichocka, A. Fijałkowska, K. P. Rykaczewski, M. Karny, R. K. Grzywacz, K. C. Goetz, C. J. Gross, D. W. Stracener, E. F. Zganjar, J. C. Batchelder, J. C. Blackmon, N. T. Brewer, S. Go, B. Heffron, T. King, J. T. Matta, K. Miernik, C. D. Nesaraja, S. V. Paulauskas, M. M. Rajabali, E. H. Wang, J. A. Winger, Y. Xiao, and C. J. Zachary

Phys. Rev. Lett. 117, 092501 – Published 22 August 2016

Abstract

We report total absorption spectroscopy measurements of ${}^{92}{Rb}$ , ${}^{96 gs}Y$ , and ${}^{142}{Cs}$ $β$ decays, which are the most important contributors to the high energy ${\bar{ν}}_{e}$ spectral shape in nuclear reactors. These three $β$ decays contribute 43% of the ${\bar{ν}}_{e}$ flux near 5.5 MeV emitted by nuclear reactors. This ${\bar{ν}}_{e}$ energy is particularly interesting due to spectral features recently observed in several experiments including the Daya Bay, Double Chooz, and RENO Collaborations. Measurements were conducted at Oak Ridge National Laboratory by means of proton-induced fission of ${}^{238}U$ with on-line mass separation of fission fragments and the Modular Total Absorption Spectrometer. We observe a $β$ -decay pattern that is similar to recent measurements of ${}^{92}{Rb}$ , with a ground-state to ground-state $β$ feeding of 91(3)%. We verify the ${}^{96 gs}Y$ ground-state to ground-state $β$ feeding of 95.5(20)%. Our measurements substantially modify the $β$ -decay feedings of ${}^{142}{Cs}$ , reducing the $β$ feeding to ${}^{142}{Ba}$ states below 2 MeV by 32% when compared with the latest evaluations. Our results increase the discrepancy between the observed and the expected reactor ${\bar{ν}}_{e}$ flux between 5 and 7 MeV, the maximum excess increases from $\sim 10 %$ to $\sim 12 %$ .

Received 4 May 2016

DOI:https://doi.org/10.1103/PhysRevLett.117.092501

Physics Subject Headings (PhySH)

Beta decay

90 ≤ A ≤ 149

Gamma ray spectroscopy

Nuclear Physics

Authors & Affiliations

B. C. Rasco^1,2,3,*, M. Wolińska-Cichocka^5,2,1, A. Fijałkowska^6,3, K. P. Rykaczewski², M. Karny^6,2,1, R. K. Grzywacz^3,2,1, K. C. Goetz^7,3, C. J. Gross², D. W. Stracener², E. F. Zganjar⁴, J. C. Batchelder^8,1, J. C. Blackmon⁴, N. T. Brewer^1,2,3, S. Go³, B. Heffron^3,2, T. King³, J. T. Matta², K. Miernik^6,1, C. D. Nesaraja², S. V. Paulauskas³, M. M. Rajabali⁹, E. H. Wang¹⁰, J. A. Winger¹¹, Y. Xiao³, and C. J. Zachary¹⁰

¹JINPA, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
²Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37966, USA
⁴Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803 USA
⁵Heavy Ion Laboratory, University of Warsaw, PL-02-093 Warsaw, Poland
⁶Faculty of Physics, University of Warsaw, PL-02-093 Warsaw, Poland
⁷CIRE Bredesen Center, University of Tennessee, Knoxville, Tennessee 37966, USA
⁸Department of Nuclear Engineering, University of California, Berkeley, Berkeley California 94720, USA
⁹Department of Physics, Tennessee Technological University, Cookeville, Tennessee 38505, USA
¹⁰Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA
¹¹Department of Physics and Astronomy, Mississippi State University, Mississippi State, Mississippi 39762, USA