Structure of high-lying levels populated in the 96Y →96Zr β decay

K.R Mashtakov,R Chapman,C Bathia,N Pietralla,B Löher,M Scheck,U Friman-Gayer,W Tornow,M Ramdhane,C Romig,P Spagnoletti,J Isaak,J Sinclair,G Rainovski,H Pai,T Beck,U Köster,K Sonnabend,M.M.R Chishti,G Rusev,M Zweidinger,D Savran,M Bowry,J Beller,L P Gaffney ,D O’donnell ,Sean Finch ,A P Tonchev ,O Ağar ,A D Maclean ,E Gregor ,P E Garrett ,G S Simpson ,J M Keatings ,V Yu Ponomarev

doi:10.1016/j.physletb.2021.136569

Abstract

The nature of the high-lying final levels of the 96Ygsβ decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum, has been investigated in high-resolution γ-ray spectroscopy following the β decay as well as in a campaign of inelastic photon scattering experiments. The comprehensive approach establishes 1− levels associated with the Pygmy Dipole Resonance as high-lying final levels in the β decay. Branching ratios extracted from β decay complement photon scattering and allow the absolute E1 excitation strength to be determined for levels populated in both reactions. The combined data represents a comprehensive approach to the wavefunction of the 1− levels below the Qβ value, which are investigated in the Quasiparticle Phonon Model. The calculations reveal that the components populated in β decay contribute only with small amplitudes to the complex wavefunction of these 1− levels. A comparison of the β decay results to data from total absorption γ-ray spectroscopy demonstrates a good agreement between both measurements.

Highlights

The nature of Jπ = 1− levels of 96Zr below the β-decay Q value of 96Y has been investigated in high-resolution γ-ray spectroscopy following the β decay as well as in a campaign of inelastic photon scattering experiments
Following the observation of a lack of high-energy antineutrinos emitted from nuclear reactors [1], nuclear β-decay studies using total absorption γ-ray spectroscopy (TAGS) have shown that a larger number of β decays populate high-lying excited levels of the daughter nucleus than hitherto believed
The average energy shared by the emitted electron and antineutrino is less than previously anticipated from β-decay studies using high resolution γray spectroscopy (HRS)

Summary

Introduction

Structure of high-lying levels populated in the 96Y →96Zr β decay Branching ratios extracted from β decay allow the absolute E1 excitation strength to be determined for levels populated in both reactions.

Results

Conclusion