Low-energy enhancement in the magnetic dipole γ-ray strength functions of heavy nuclei

Fanto, Paul; Alhassid, Yoram

doi:10.1103/physrevc.109.l031302

Low-energy enhancement in the magnetic dipole γ-ray strength functions of heavy nuclei

Journal Article · Thu Mar 07 00:00:00 EST 2024 · Physical Review. C

DOI:https://doi.org/10.1103/physrevc.109.l031302· OSTI ID:2378620

Fanto, Paul ^[1]; ^[2]

Yale University, New Haven, CT (United States); Yale University
Yale University, New Haven, CT (United States)

A low-energy enhancement (LEE), which was observed experimentally in the gamma-ray strength function (γSF) describing the decay of compound nuclei, would have profound effects on r-process nucleosynthesis if it persists in heavy neutron-rich nuclei. The LEE was shown to be a feature of the magnetic dipole (M1) strength function in configuration-interaction shell-model calculations in medium-mass nuclei. However, its existence in heavy open-shell nuclei remains an open question. Here, using a combination of many-body methods, we identify a LEE in the M1 γSFs of heavy samarium nuclei. In particular, we use the static-path plus random-phase approximation (SPA+RPA), which includes static and small-amplitude quantal fluctuations beyond the mean field. Using the SPA+RPA strength as a prior, we apply the maximum-entropy method (MEM) to obtain finite-temperature M1 γSFs from exact imaginary-time response functions calculated with the shell model Monte Carlo (SMMC) method. We find that the slope of the LEE in samarium isotopes is roughly independent of the average initial energy over a wide range below the neutron separation energy. As the neutron number increases, strength transfers to a low-energy excitation, which we interpret as the scissors mode built on top of excited states.

View Accepted Manuscript (DOE)

Research Organization:: Yale University, New Haven, CT (United States)

Sponsoring Organization:: USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)

Grant/Contract Number:: AC02-05CH11231; NA0003960; SC0019521

OSTI ID:: 2378620

Alternate ID(s):: OSTI ID: 2474375

Journal Information:: Physical Review. C, Journal Name: Physical Review. C Journal Issue: 3 Vol. 109; ISSN 2469-9985

Publisher:: American Physical Society (APS)Copyright Statement

Country of Publication:: United States

Language:: English

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