Evidence for enhanced neutron-proton correlations from the level structure of the $N=Z+1$ nucleus $^{87}_{43}$Tc$^{\ }_{44}$

TL;DR

This study investigates the level structure of the neutron-deficient nucleus $^{87}$Tc, revealing rotational behavior and evidence for enhanced neutron-proton correlations near the $N=Z$ line through experimental gamma-ray spectroscopy.

Contribution

The paper provides the first detailed level scheme of $^{87}$Tc and links observed rotational features to enhanced neutron-proton correlations in odd-mass nuclei near $N=Z$.

Findings

Level scheme from 9/2+ to 33/2+ states established

Rotational behavior with sharp backbending observed

Enhanced neutron-proton correlations inferred near $N=Z$ line

Abstract

The low-lying excited states in the neutron-deficient $N=Z+1$ nucleus $^{87}_{43}$Tc$^{\ }_{44}$ have been studied via the fusion-evaporation reaction $^{54}$Fe($^{36}$Ar, $2n1p$)$^{87}$Tc at the Grand Acc\'el\'erateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt $\gamma$-rays, neutrons, and charged particles emitted in the reaction. A level scheme of $^{87}$Tc from the (9/2$^{+}_{g.s.}$) state to the (33/2$^{+}_{1}$) state was established based on 6 mutually coincident $\gamma$-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at $\hbar\omega\approx 0.50$ MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around $N=44$ is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the $N=Z$ line.