Competition between Allowed and First-Forbidden β Decay: The Case of ^{208}Hg→^{208}Tl.

R Carroll ,R Shearman,Z Patel,C Fahlander,T Berry,S Lalkovski,H Grawe,E Nácher,T Alexander,P Van Duppen,V Vedia,M Huyse,T Stora,R Lică,S Pascu,I Kuti,P Rahkila,J Konki,S Stegemann,J Phrompao,A Gredley,J Kurcewicz,Ch Sotty,O Tengblad,W Gelletly,V Pucknell,Zs Podolyák,N Warr,R.-B Gerst,H De Witte,M Piersa,M Rudigier,R Wadsworth,C Mihai,F Wearing,M Madurga,E Rapisarda,F Rotaru,M Górska,Á Perea ,P T Greenlees ,C Shand ,P H Regan ,L J Harkness-Brennan ,I Marroquín ,R Mihai ,H O U Fynbo ,L M Fraile ,R Mărginean ,S M Razaullah Ansari ,J R Creswell ,Cristina Niță ,A Negreţ ,P M Walker ,M V Lund ,E R Gamba ,D S Judson ,N Mărginean ,A N Andreyev ,R D Page ,Michel Brunet ,I Lazarus ,Steven Judge ,M J G Borge

doi:10.1103/physrevlett.125.192501

Abstract

The β decay of ^{208}Hg into the one-proton hole, one neutron-particle _{81}^{208}Tl_{127} nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z<82 quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the Q_{β} window, only three negative parity states are populated directly in the β decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden β decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process. Furthermore, the observation of the parity changing 0^{+}→0^{-}β decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.

Highlights

The β decay of 208Hg into the one-proton hole, one neutron-particle 28018Tl127 nucleus was investigated at CERN-ISOLDE
The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden β decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process
The A ∼ 195 r-process abundance peak is the consequence of the N 1⁄4 126 neutron shell closure. β-decay half-lives are basic nuclear physics input in r-process calculations

Summary

Introduction

The β decay of 208Hg into the one-proton hole, one neutron-particle 28018Tl127 nucleus was investigated at CERN-ISOLDE. The observation of the parity changing 0þ → 0−β decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators. An ideal nucleus to study the competition between FF and allowed β decay should have a small number of both negative and positive parity levels below the Qβ value, with simple and well-understood wave functions.

Objectives

Results

Conclusion