Optical model analysis of the elastic scattering of 20–24 MeV α-particles by 12C, 14N, 16O and 20Ne

doi:10.1016/0375-9474(77)90683-2

Nuclear Physics A

Volume 284, Issue 1, 27 June 1977, Pages 29-40

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Abstract

An optical model analysis is presented for angular distributions of elastic scattering of 20 to 24 MeV α-particles from ¹²C, ¹⁴N, ¹⁶O and ²⁰Ne. Families of parameters are found characterised by differences in the volume integral per interacting nucleon pair for the real potential of the order of 100 MeV · fm³, in agreement with similar analysis fir heavier targets. The value of the real potential at an equivalent semiclassical strong absorption radius is shown to be a significant parameter in this analysis, again in agreement with results for heavier targets. A characteristic of most of the optical model fits is the very small value of the imaginary surface diffuseness parameter.

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The ¹⁶O + ¹²C elastic scattering data have been well described, for the first time, with a shallow folded potential obtained from a single folding method. The constituent parameters of the potential, excepting one, for its real part are generated from the nucleon–¹⁶O and α–¹⁶O potentials, and the cluster structure of ¹²C. Only the repulsive part of the α–¹⁶O potential needs some adjustment to fit the data, reflecting the need to include the Pauli exclusion effects among the unclustered nucleons.
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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, v_sar, 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.
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2. •
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Optical model analysis of the elastic scattering of 20–24 MeV α-particles by 12C, 14N, 16O and 20Ne

Abstract

Phys. Lett.

Phys. Rev.

An. Real. Soc. Esp. Fis. Quim.

Phys. Reports

Phys. Rev.

Phys. Rev.

Phys. Rev.

Phys. Rev.

Phys. Rev.

Phys. Rev.

J. Phys. Soc. Japan

J. Phys. Soc. Japan

Phys. Rev.

Phys. Rev.

J. Phys. Soc. Japan

Optical model analysis of the elastic scattering of 20–24 MeV α-particles by ¹²C, ¹⁴N, ¹⁶O and ²⁰Ne