First observation of low-energy {\gamma}-ray enhancement in the rare-earth region

TL;DR

This study reports the first observation of low-energy gamma-ray enhancement in the rare-earth nucleus 151,153Sm, revealing new nuclear structure phenomena and potential implications for astrophysical nucleosynthesis models.

Contribution

It presents the first measurement of low-energy gamma-ray strength in the rare-earth region, including the simultaneous observation of the upbend and scissors resonance in 151,153Sm.

Findings

Detected gamma-ray strength enhancement down to 500 keV.

Observed both upbend and scissors resonance in the same nucleus.

Indicates significant impact on r-process nucleosynthesis reaction rates.

Abstract

The {\gamma}-ray strength function and level density in the quasi-continuum of 151,153Sm have been measured using BGO shielded Ge clover detectors of the STARLiTeR system. The Compton shields allow for an extraction of the {\gamma} strength down to unprecedentedly low {\gamma} energies of about 500 keV. For the first time an enhanced low- energy {\gamma}-ray strength has been observed in the rare-earth region. In addition, for the first time both the upbend and the well known scissors resonance have been observed simultaneously for the same nucleus. Hauser-Feshbach calculations show that this strength enhancement at low {\gamma} energies could have an impact of 2-3 orders of magnitude on the (n,{\gamma}) reaction rates for the r-process nucleosynthesis.