Continuing influence of shell effects at high-excitation energies

How do we infer shell effects at high-excitation energies? A new spectroscopic probe to search for magic numbers

“…Recent studies of f (E γ ) by Guttormsen and co-workers support the validity of the Brink-Axel hypothesis at different bin energies in the quasi-continuum region [46]. This, together with the fact that GDR studies of nuclei at relatively low temperatures T and spins J and cold nuclei in their ground state present similar features [47,48], may allow for combining the LEE and GDR cross sections [4]. As shown in Figs.…”

“…In this work, we propose an alternative spectroscopic probe, namely the nuclear polarizability, to investigate the rise of magic numbers at high-excitation energies. This work expands on the data analysis of our recent publications [4,5] by doing a systematics study for the limited available information and assuming that the enhancement of the photon-strength function continues at lower gamma-ray energies of E γ ≧ 0.1 MeV. Overall, this cutoff shows a greater sensitivity of the nuclear polarizability to the long-range correlations in the nuclear wave functions, as realized from relative sharp drops of the nuclear polarizability in semi-magic nuclei.…”

“…The sudden drop of σ −2 values and κ < 1 for nuclei with neutron magic numbers N = 28, 50 and 82 supports the M1 nature of the LEE predicted by large-scale SM calculations and the validity of the generalized Brink-Axel hypothesis, which seems to allow for structural changes. This work emphasizes the need for additional f (E γ ) measurements at low energies below 1 MeV, and opens a new research avenue to investigate the existence and evolution of magic numbers at high-excitation energies from σ −2 measurements [4].…”

“…Most nuclei present an energy gap with missing data between the LEE and GDR data, which may include the M1 spin-flip resonance and the pygmy dipole resonances (PDR) in neutron-rich nuclei. Therefore, data from ENDF [43] -when availablehave been used to fill the gap [4,5]. Additionally, data near nucleon threshold energies generally present large uncertainties and have been excluded.…”

Combined analysis of the low-energy enhancement of the gamma-strength function and the giant dipole resonance

“…Recent studies of f (E γ ) by Guttormsen and co-workers [39] in the LEE region support the validity of the Brink-Axel hypothesis at different excitation energies. This, together with the fact that GDR studies of hot nuclei (at relatively low temperatures T and spin J ) and cold nuclei (T = 0 for the ground state) present similar features [9,40], may allow for combining the LEE and GDR cross sections [41].…”