Verification of detailed balance for $\gamma$ absorption and emission in Dy isotopes

TL;DR

This study measures photo-neutron cross sections of Dy isotopes, confirms detailed balance, and establishes a comprehensive gamma-ray strength function that supports the Brink hypothesis and accurately predicts neutron-capture cross sections.

Contribution

First measurement of photo-neutron cross sections for $^{162,163}$Dy up to 13 MeV, confirming detailed balance and establishing a complete gamma-ray strength function for these isotopes.

Findings

Photo-neutron cross sections measured for the first time.

Confirmed the principle of detailed balance.

Predicted neutron-capture cross sections agree with direct measurements.

Abstract

The photo-neutron cross sections of $^{162,163}\rm{Dy}$ have been measured for the first time in an energy region from the neutron threshold ($S_n$) up to $\approx$ $13$~MeV. The ($\gamma$,n) reaction was induced with quasi-monochromatic laser Compton-scattered $\gamma$ rays, produced at the NewSUBARU laboratory. The corresponding $\gamma$-ray strength functions ($\gamma$SF) have been calculated from the photo-neutron cross sections. The data are compared to reanalyzed $\gamma$SFs of $^{160-164}\rm{Dy}$, which are measured below $S_n$. The excellent agreement with the photo-neutron data at $S_n$ confirms the principle of detailed balance. Thus, a complete $\gamma$SF is established covering in total the energy region of 1 MeV $\leq$ E$_{\gamma}$ $\leq$ 13 MeV. These mid-shell well-deformed dysprosium isotopes all show scissors resonances with very similar structures. We find that our data predict the same integrated scissors strength as ($\gamma,\gamma^\prime$) data when integrated over the same energy range, which shows that the scissors mode very likely is consistent with the generalized Brink hypothesis. Finally, using the $\gamma$SFs as input in the reaction code TALYS, we have deduced radiative neutron-capture cross sections and compared them to direct measurements. We find a very good agreement within the uncertainties, which gives further support to the experimentally determined $\gamma$SFs.