Programme

O.22 -- Oral, VCTP-51

Date: Tuesday, 4 August 2026

Time: 15:00-15:20

Low-Energy Enhancement in the Gamma-Ray Strength Function

Le Tan Phuc (1,2), Nguyen Ngoc Anh (3), Nguyen Quang Hung (1,2), and Nguyen Dinh Dang (4)

(1) Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh City 70000, Vietnam (2) Faculty of Natural Sciences, Duy Tan University, Da Nang City 55000, Vietnam (3) Phenikaa Institute for Advanced Study (PIAS), PHENIKAA University, Hanoi, 12116, Vietnam (4) Nuclear Many-Body Theory Laboratory, RIKEN Nishina Center for Accelerator-Based Science, 2-1 Hirosawa, Wako City, 351-0198 Saitama, Japan

The low-energy enhancement (LEE), also known as the upbend resonance (UBR), observed in the gamma-ray strength function has attracted considerable attention because of its significant impact on neutron-capture reactions and astrophysical nucleosynthesis. Despite extensive experimental evidence, its microscopic origin remains an open question. In this talk, we present a new microscopic description of the UBR based on the exact thermal pairing plus phonon-damping model. Our calculations demonstrate that the UBR emerges only at finite temperature and originates from non-collective particle-particle and hole-hole excitations. These results provide a microscopic explanation for the observed low-energy enhancement and offer strong theoretical evidence that the Brink-Axel hypothesis is violated in the very low-Eγ region. Key words: gamma-ray strength function, Upbend resonance, Brink-Axel hypothesis, Exact pairing solution, Phonon Damping Model

Presenter: Le Tan Phuc