Neutron Halos in Excited States of 12B

A Danilov,T Belyaeva,Y Sobolev,W Trzaska,Y Gurov,S Khlebnikov,E Mukhamejanov,V Maslov,A Demyanova,G Tyurin,S Goncharov,N Burtebaev,D Janseitov,R Sukhorukov,A Ogloblin

doi:10.18502/ken.v3i1.1727

Abstract

An experiment was done to search for states with a neutron halo in 12B. The measurements were carried out at the cyclotron of the University of Jyvaskyla (Finland) using Large Scattering Chamber (LSC). The idea of the work was to search for two states with the expected neutron halo, 1 ̄ and 2 ̄. Differential cross sections with excitation of 12B states, including abovementioned states, were observed. The preliminary calculations on halo radii by the method of asymptotic normalization coefficients for the 2 ̄ and 1 ̄ states which are in a discrete spectrum gave following values: 5.6 fm and 7.4 fm, which is much larger than the radius of the valence neutron in the ground state. But strictly the presence of a neutron halo can be confirmed only for 1 ̄ state. The 2 ̄ state can be considered only as candidate for halo. An unexpected result was obtained for the 3 ̄, 3.39 MeV state, which is in continuum 19 keV above the decay threshold 12B → 11B + n, preliminary estimation for its halo radius is ∼ 6.5 fm. This indicates that the halo can be present in this state as well. But strict conditions for neutron halo are not fulfilled in the same way as for 2 ̄ state. Until now, the neutron halo in unbound states has been observed only for the members of the rotational bands.

Highlights

The evidence of the excited states of light nuclei with nonstandard sizes and enlarged radii, located closely and above the particle-emission threshold, was convincingly demonstrated
Liu et al [2] reported the observation of halos in the first (1/2+, Ex = 3.089 MeV) excited state of 13C, and the second (2 ̄, Ex = 1.674 MeV) and third (1 ̄, Ex = 2.621 MeV) excited states of 12B using the (d,p) reactions on 12C and 11B, respectively, by analyzing the data with the ANC method
We present the results of the measurement and analysis of the 11B(d,p)12B reaction populated the 1+ g.s. and five excited states up to the neutronemission threshold: 0.953 MeV 2+, 1.674 MeV 2 ̄, 2.621 MeV 1 ̄, 2.723 MeV 0+, and 3.389 MeV 3 ̄ states, at incident deuteron energy Elab = 21.5 MeV

Summary

Introduction

The evidence of the excited states of light nuclei with nonstandard sizes and enlarged radii, located closely and above the particle-emission threshold, was convincingly demonstrated (see, e.g., Ref. [1] and references therein). The evidence of the excited states of light nuclei with nonstandard sizes and enlarged radii, located closely and above the particle-emission threshold, was convincingly demonstrated ICPPA 2017 of neutron halos in the short-lived excited states of some stable and radioactive nuclei was revealed, in particular, by the ANC analysis of the neutron-transfer reactions [2,3,4]. We present the results of the measurement and analysis of the 11B(d,p)12B reaction populated the 1+ g.s. and five excited states up to the neutronemission threshold: 0.953 MeV 2+, 1.674 MeV 2 ̄, 2.621 MeV 1 ̄, 2.723 MeV 0+, and 3.389 MeV 3 ̄ states, at incident deuteron energy Elab = 21.5 MeV.

Experiment

Findings

Analysis of the results