Shell-gap reduced level densities in $^{89,90}$Y

TL;DR

This paper investigates how the N=50 shell closure affects nuclear level densities in yttrium isotopes using particle-$\gamma$ coincidences and the Oslo method, revealing shell effects in the level density structure.

Contribution

It applies the Oslo method to measure level densities in $^{89,90}$Y and discusses shell closure effects with a combinatorial quasi-particle model, providing new insights into nuclear structure.

Findings

Shell effects are observed in the level densities.

The N=50 shell closure influences the level density structure.

The combinatorial quasi-particle model explains the observed shell effects.

Abstract

Particle-$\gamma$ coincidences from the $^{89}$Y($p,p' \gamma$)$^{89}$Y and $^{89}$Y($d,p \gamma$)$^{90}$Y reactions were utilized to obtain $\gamma$-ray spectra as function of excitation energy. The Oslo method was used to extract the level density from the particle-$\gamma$ coincidence matrices. The impact of the $N=50$ shell closure on the level densities is discussed within the framework of a combinatorial quasi-particle model.