Experimental signature of collective enhancement in nuclear level density

Abstract

We present a probable experimental signature of collective enhancement in the nuclear level density (NLD) by measuring the neutron and the giant dipole resonance (GDR) $\gamma$ rays emitted from the rare earth ${}^{169}$Tm compound nucleus populated at 26.1 MeV excitation energy. An enhanced yield is observed in both neutron and $\gamma$ ray spectra corresponding to the same excitation energy in the daughter nuclei. The enhancement could only be reproduced by including a collective enhancement factor in the Fermi gas model of NLD to explain the neutron and GDR spectra simultaneously. The experimental results show that the relative enhancement factor is of the order of 10 and the fadeout occurs at $\sim$ 14 MeV excitation energy, much before the commonly accepted transition from deformed to spherical shape. We also explain how the collective enhancement contribution changes the inverse level density parameter ($k$) from 8 to 9.5 MeV observed recently in several deformed nuclei.

arXiv comment6 pages, 4 figures, Accepted in Phys. Rev. C (Rapid Communications)

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Cited by in corpus (5)

• Strong enhancement of level densities in the crossover from spherical to deformed neodymium isotopes
• Alleviating the inconsistencies in modelling decay of fissile compound nuclei
• Evidence for the reduction of nuclear level density away from the $\beta$-stability line
• Weak-coupling to unitarity crossover in Bose-Fermi mixtures: Mixing-demixing and spontaneous symmetry breaking in trapped systems
• Nuclear level densities away from line of $\beta$-stability