6533b85dfe1ef96bd12be59b

RESEARCH PRODUCT

The elastic scattering of 25MeV α-particles and neutron shell effects in the A = 50 TO A = 93 mass region

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Abstract Experimental elastic scattering angular distributions of 25 MeV α-particles scattered from 28 nuclei ranging from 50Cr to 93Nb have been measured and then analysed in terms of a regular optical model with standard Woods-Saxon geometries for both the real and imaginary potentials. The experimental distributions are well fitted over the whole angular range from 5° to 175° c.m. by the predictions, provided that a smaller than normal diffuseness is used for the imaginary potentials. The usual families of potentials with volume integrals differing by approximately 100 MeV · fm3 are found. The family with volume integral ranging from 540 to 420 MeV· fm3 over the nuclei studied has been chosen as the most appropriate, corresponding to the single family found for α-particle elastic scattering at above 100 MeV. When plotted as functions of the back-angle enhancement parameter γ(θ), the derived parameter at the strong absorption radius, vsar, shows clear grouping into nuclei with similar neutron shell configurations. The derived optical model rms radii also show an abrupt change at the N = 40 neutron sub-shell closure. These effects are shown to be consistent with a contribution to the α-nucleus potential from the neutron pairing interaction.