Statistical γ -decay properties of Ni 64 and deduced (n,γ) cross section of the s -process branch-point nucleus Ni 63

Particle-γ coincidence data have been analyzed to obtain the nuclear level density and the γ-strength function of Ni64 by means of the Oslo method. The level density found in this work is in very good agreement with known energy levels at low excitation energies as well as with data deduced from particle-evaporation measurements at excitation energies above Ex≈5.5 MeV. The experimental γ-strength function presents an enhancement at γ energies below Eγ≈3 MeV and possibly a resonancelike structure centered at Eγ≈9.2 MeV. The obtained nuclear level density and γ-strength function have been used to estimate the (n,γ) cross section for the s-process branch-point nucleus Ni63, of particular interest for astrophysical calculations of elemental abundances. © 2016 American Physical Society

On the X(17) light-particle candidate observed in nuclear transitions

Recently, we observed an anomalous internal pair creation for the M1 transition depopulating the 18.15 MeV isoscalar 1+ state in 8Be. The deviation from the theoretical prediction can be described by assuming the creation and subsequent decay of a new, light boson with a mass of 16.7 MeV/c2. In order to clarify the interpretation, we re-investigated the 8Be anomaly with an improved and independent setup. We have confirmed the signal of the assumed X(17) particle and constrained its mass (m0c2= 17.01(16) MeV) and branching ratio compared to the γ-decay (Bx=6(1)x10−6). We investigated also the high-energy (21 MeV) J=0−->0+ transition in 4He and got a consistent result for the X(17) particle