Decays of the Three Top Contributors to the Reactor ν[over ¯]_{e} High-Energy Spectrum, ^{92}Rb, ^{96gs}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; C J Zachary

doi:10.1103/PhysRevLett.117.092501

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

Phys Rev Lett. 2016 Aug 26;117(9):092501. doi: 10.1103/PhysRevLett.117.092501. Epub 2016 Aug 22.

Authors

B C Rasco^{1

2

3}, M Wolińska-Cichocka^{1

2

4}, A Fijałkowska^{3

5}, K P Rykaczewski², M Karny^{1

2

5}, R K Grzywacz^{1

2

3}, K C Goetz^{3

6}, C J Gross², D W Stracener², E F Zganjar⁷, J C Batchelder^{1

8}, J C Blackmon⁷, N T Brewer^{1

2

3}, S Go³, B Heffron^{2

3}, T King³, J T Matta², K Miernik^{1

5}, C D Nesaraja², S V Paulauskas³, M M Rajabali⁹, E H Wang¹⁰, J A Winger¹¹, Y Xiao³, C J Zachary¹⁰

Affiliations

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

PMID: 27610847
DOI: 10.1103/PhysRevLett.117.092501

Abstract

We report total absorption spectroscopy measurements of ^{92}Rb, ^{96gs}Y, and ^{142}Cs β decays, which are the most important contributors to the high energy ν[over ¯]_{e} spectral shape in nuclear reactors. These three β decays contribute 43% of the ν[over ¯]_{e} flux near 5.5 MeV emitted by nuclear reactors. This ν[over ¯]_{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 ^{96gs}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 ν[over ¯]_{e} flux between 5 and 7 MeV, the maximum excess increases from ∼10% to ∼12%.