Exploring the spin states of90Zr populated by (p,p’), (p,d), and (p,t) reactions

S Ota,H I Park,R.O Hughes,N.J Foley,J.T Burke,E Mccleskey,R.A.E Austin,T J Ross,J.E Escher,B Abromeit,M Mccleskey,N.D Scielzo,J.J Ressler,A Saastamoinen,R.J Casperson,I.J Thompson

doi:10.1051/epjconf/201612212003

Abstract

The 90 Zr nucleus was produced by three different reactions: 90 Zr( p , p ’), 91 Zr( p , d ), and 92 Zr( p , t ), and the spin-parity ( J π ) population of the 90 Zr states produced by these reactions was studied to investigate the surrogate reaction approach, which aims at indirectly determining cross sections for compound-nuclear reactions involving unstable targets such as 89 Zr( n , γ ). Discrete γ-rays, associated with the de-excitation of 90 Zr and 89 Zr, were measured in coincidence with light ions at 90 Zr excitation energies extending above the neutron separation energy. Low-lying states populated by ( p , d ) and ( p , t ) reactions agreed well with the previous measurements. The measured γ transition systematics were used to gain insights into the J π distribution of 90 Zr around the neutron separation energy and it was found that the ( p , p ’) reaction preferentially produces lower J states than ( p , d ) and ( p , t ) reactions in the studied energy region.

Highlights

Radiative neutron-capture (n,γ) cross sections at neutron energies of a few tens of keV to a few MeV are crucial inputs for nuclear-energy applications, astrophysical studies, and radiochemical applications
The outgoing particle from the surrogate reaction is detected in coincidence with an observable that is characteristic of the decay channel of interest and the measured coincidence probability is used to constrain the reaction cross section
A primary difficulty in determining (n,γ) cross sections is the difference in the spin-parity (Jπ) distributions of the compound nucleus created by the (n,γ) and the surrogate reactions

Summary

Introduction

Radiative neutron-capture (n,γ) cross sections at neutron energies of a few tens of keV to a few MeV are crucial inputs for nuclear-energy applications, astrophysical studies, and radiochemical applications. The cross sections for most short-lived isotopes remain poorly known due to their inaccessibility as target materials. To address this problem, various types of indirect methods to infer the (n,γ) cross sections have been investigated, such as the surrogate reaction method [1,2,3,4]. In order to extract (n,γ) cross sections from surrogate data, it becomes necessary to take into account the Jπ distribution of the decaying compound nucleus. Details about the modelling based on the γ-ray decay probabilities can be found in [10] With this background, we studied spin states in the nucleus 90Zr populated by 90Zr(p,p’)90Zr, 91Zr(p,d)90Zr, 92Zr(p,t)90Zr reactions. The low level densities in the Zr mass region due to the presence of closed proton and neutron shells, leads to a competition between γ decay and neutron emission that is sensitive to the Jπ distributions of the decaying compound nuclei and can be expected to be visible in the measured discrete γ-ray emission probabilities

Experiment

Particle singles spectra

Spin population in continuum region

Below the neutron separation energy

Above the neutron separation energy

Summary and Outlook