Year: 2025
Type: article
Abstract: The low-energy enhancement (LEE) in γ-ray strength functions has been experimentally identified in a large number of nuclei during the past two decades; however, the origin of the enhancement is not fully understood. Building on previous theoretical work, we investigate the LEE and its relation to the scissors mode (SM) with an independent theoretical approach. We apply a novel angular-momentum-projected shell-model method that explicitly endows degrees of freedom to describe the scissors motion. Taking the recently measured γ-ray strength functions in Neodymium isotopes as examples, we find that the LEE arises from a quasi-free scissors motion appearing only in weakly-deformed nuclei, which can be viewed as an approximate free-rotation of neutrons with respect to protons. This leads us to propose a new type of collective motion, scissors rotation, to contrast the scissors vibration widely known in well-deformed nuclei. The observed LEE is naturally interpreted as the first evidence for this collective excitation mode.
Source: Physical Review Letters
Authors: Fang-Qi Chen, Y. F. Niu, Yang Sun, Mathis Wiedeking
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: U.S. Department of Energy, Lanzhou University, National Research Foundation, National Natural Science Foundation of China, Office of Science, National Key Research and Development Program of China, Fundamental Research Funds for the Central Universities, Nuclear Physics, Lawrence Berkeley National Laboratory
OpenAlex ID: W4408054629