Production cross sections from 82Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line

TL;DR

This study measures production cross sections of neutron-rich isotopes from 82Se fragmentation, revealing shell effects near the neutron drip-line and confirming a subshell closure at N=34 through experimental data and theoretical modeling.

Contribution

It provides new experimental data on neutron-rich isotopes near the drip-line and demonstrates shell effects consistent with shell model predictions at N=34.

Findings

Identification of the most neutron-rich isotopes for elements 22-25.

Confirmation of a subshell closure at N=34.

Data consistent with shell model and Abrasion-Ablation calculations.

Abstract

Production cross sections for neutron-rich nuclei from the fragmentation of a 82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions of 126 neutron-rich isotopes of elements 11 <= Z <= 32 were scanned using an experimental approach of varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including several isotopes first observed in this work. These are the most neutron-rich nuclides of the elements 22 <= Z <= 25 (64Ti, 67V, 69Cr, 72Mn). One event was registered consistent with 70Cr, and another one with 75Fe. The production cross sections are correlated with Qg systematics to reveal trends in the data. The results presented here confirm our previous result from a similar measurement using a 76Ge beam, and can be explained with a shell model that predicts a subshell closure at N = 34 around Z = 20. This is demonstrated by systematic trends and calculations with the Abrasion-Ablation model that are sensitive to separation energies.