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

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.