Formula omitted], a quasi-free neutron decay?

K Riisager,O Forstner,G Nyman,A Heinz,M Carmona-Gallardo,T Giles,R Thies,T Nilsson,A Gottberg,E Rapisarda,J Kurcewicz,O Tengblad,B Jonson,H O U Fynbo ,Peter Steier ,Jacob Johansen ,J A Briz ,María José García Borge ,L M Fraile ,M V Lund ,Stephan Winkler

doi:10.1016/j.physletb.2014.03.062

Abstract

We have observed β−-delayed proton emission from the neutron-rich nucleus 11Be by analyzing a sample collected at the ISOLDE facility at CERN with accelerator mass spectrometry (AMS). With a branching ratio of (8.3±0.9)⋅10−6 the strength of this decay mode, as measured by the BGT-value, is unexpectedly high. The result is discussed within a simple single-particle model and could be interpreted as a quasi-free decay of the 11Be halo neutron into a single-proton state.

Highlights

Beta-minus decay and proton emission take a nucleus in almost opposite directions on a nuclear chart, so β−-delayed proton emission is forbidden in all but a few nuclei where it is heavily suppressed as the available energy is [1] Q βp = 782 keV − Sn, where Sn is the neutron separation energy of the nucleus
We describe here an experiment to detect this decay mode from the one-neutron halo nucleus 11Be that is believed to be the most favourable case [2,3] due to the single-particle behaviour of halo nuclei [4,5,6] that may favour this decay mode and due to the relatively long halflife that is caused by the normal beta-decay of 11Be being hindered since a level inversion gives it a 1/2+ ground state rather than a 1/2−
Most of the backscattered ions are expected to remain close to the sample so γ -rays from their decays will be seen as well, the decay products are not retained in the sample

Summary

Introduction

The βp decay mode may be expected preferentially in oneneutron halo nuclei, partly due to the requirement of low neutron separation energy, partly due to the more pronounced singleparticle behaviour of halo nuclei. Converting the observed spectra for beta-delayed deuteron emission from the two-neutron halo nuclei. Most of the backscattered ions are expected to remain close to the sample so γ -rays from their decays will be seen as well, the decay products are not retained in the sample. This gives a correction which we estimate to be 4 ± 4%

General remarks

Sample collection

Possible contaminants

Findings

Discussion

Conclusion