Inverse-kinematics one-neutron pickup with fast rare-isotope beams

TL;DR

This paper reports on new measurements and reaction model calculations for one-neutron pickup reactions on fast Mg beams, revealing the reaction mechanisms and potential for studying single-particle states in exotic nuclei.

Contribution

It provides the first investigation of the pickup reaction mechanism at high energies using thick targets and -ray spectroscopy, demonstrating the reaction's direct two-body nature and potential for nuclear structure studies.

Findings

Reaction on  target proceeds as a direct two-body process.

Reaction on  target leaves  residual unbound at high excitation.

Method allows low-rate experiments with final-state resolution.

Abstract

New measurements and reaction model calculations are reported for single neutron pickup reactions onto a fast \nuc{22}{Mg} secondary beam at 84 MeV per nucleon. Measurements were made on both carbon and beryllium targets, having very different structures, allowing a first investigation of the likely nature of the pickup reaction mechanism. The measurements involve thick reaction targets and $\gamma$-ray spectroscopy of the projectile-like reaction residue for final-state resolution, that permit experiments with low incident beam rates compared to traditional low-energy transfer reactions. From measured longitudinal momentum distributions we show that the $\nuc{12}{C} (\nuc{22}{Mg},\nuc{23}{Mg}+\gamma)X$ reaction largely proceeds as a direct two-body reaction, the neutron transfer producing bound \nuc{11}{C} target residues. The corresponding reaction on the \nuc{9}{Be} target seems to largely leave the \nuc{8}{Be} residual nucleus unbound at excitation energies high in the continuum. We discuss the possible use of such fast-beam one-neutron pickup reactions to track single-particle strength in exotic nuclei, and also their expected sensitivity to neutron high-$\ell$ (intruder) states which are often direct indicators of shell evolution and the disappearance of magic numbers in the exotic regime.