The γ-ray spectroscopy studies of low-spin structures in 210Bi and 206Tl using cold neutron capture reactions

N Cieplicka-Oryńczak ,G S Simpson ,S Leoni ,F C L Crespi ,B Fornal ,C Michelagnoli ,G Benzoni ,G De France ,Ł W Iskra ,M Jentschel ,N Pietralla ,C A Ur ,U Köster ,S Bottoni ,P Mutti ,D Bazzacco ,A Blanc ,T Söldner ,A Bracco ,W Urban ,V Werner

doi:10.1051/epjconf/201819305007

Abstract

The γ-coincidence studies of low-spin structures of 210Bi and 206Tl are presented. The 210Bi nucleus, populated in thermal neutron capture reaction, was investigated using EXILL HPGe array at Institut Laue-Langevin in Grenoble. The experimental results were compared to the shell-model calculations allowing to draw the conclusions on the nature of the low-spin excitations populated below the neutron binding energy in 210Bi (4.6 MeV). It has been found that some levels cannot be described by the valence proton and neutron couplings, but may arise from couplings of valence particles to the 3- octupole phonon of the doubly magic 208Pb core. Moreover, preliminary results of a low-spin structure measurements of 206Tl by the γ-coincidence technique, making use of the 205Tl(n,γ)206Tl reaction at the FIPPS prompt γ-ray spectroscopy facility of ILL are shown. The population of a large number of excited states of 206Tl above the ground state up to the neutron binding energy (at 6.5 MeV), within a few units of spin is expected. The analysis involving double and triple γ-coincidences and γγ-angular correlations will allow to significantly extend the experimental information on the energy and spin-parity of the levels in 206Tl. This will help shedding light on the proton-hole and neutron-hole couplings near the doubly magic core 208Pb.

Highlights

Nuclei from vicinity of doubly-closed shells play an important role in studying both: a) the couplings between valence nucleons, being a source of information on the effective nucleon-nucleon interaction and, b) couplings of the valence nucleons with core excitations
The experimental results were compared to the shell-model calculations allowing to draw the conclusions on the nature of the low-spin excitations populated below the neutron binding energy in 210Bi (4.6 MeV)
We report preliminary results of the γ-coincidence measurements of 210Bi and 206Tl, performed at the Institut Laue-Langevin (Grenoble, France) by employing the thermal neutron capture reaction and the two multidetector germanium arrays: a) EXILL in the 210Bi case [9, 10] and, b) the new FIPPS array for 206Tl

Summary

Introduction

Nuclei from vicinity of doubly-closed shells play an important role in studying both: a) the couplings between valence nucleons, being a source of information on the effective nucleon-nucleon interaction and, b) couplings of the valence nucleons with core excitations. In this way they provide a unique opportunity of testing various effective interactions used in mean-field based models, like. Four excitations involving the promotion of a neutron through the energy gap separating neutron shells at N = 126 have been located at 4.2-4.5 MeV in the 205Tl(d,p)206Tl reaction [6], i.e., the members of the πs−1/12νd5+/12 configurations. We report preliminary results of the γ-coincidence measurements of 210Bi and 206Tl, performed at the Institut Laue-Langevin (Grenoble, France) by employing the thermal neutron capture reaction and the two multidetector germanium arrays: a) EXILL in the 210Bi case [9, 10] and, b) the new FIPPS array for 206Tl

Experimental setup and results

Searching for excitations arising from the particle-phonon couplings

Experimental setup: the FIPPS array

Preliminary data analysis and shell-model interpretation

Conclusions and summary