Microscopic investigations of the backward angle anomaly in elastic α-40Ca scattering

doi:10.1016/0375-9474(78)90291-9

Nuclear Physics A

Volume 302, Issue 1, 12 June 1978, Pages 134-158

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Abstract

Elastic α-scattering on ⁴⁰Ca is studied microscopically by the resonating group method (RGM). Absorption effects are simulated by an imaginary potential whose spatial structure is taken to be proportional to the RGM overlap exchange kernel. The experimentally well-known backward anomaly is reproduced by the calculated angular distributions, and a clear connection between the P_l² structures at backward angles and l-phase-shift resonances is shown. In this context the consistency of various methods of defining resonances in the presence of absorption is investigated.

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Phase-shift analysis of d-α elastic scattering between 3 and 43 MeV
1983, Nuclear Physics, Section A
Phase shifts for the d-α elastic scattering have been extracted from differential cross sections and the vector and tensor analyzing powers of $^{4} He(d, d)^{4}$ He scattering in the energy range from 3 to 43 MeV. The analysis includes spin-orbit splitting, mixing of states and absorption to reaction channels. A new parametrization of two-channel scattering matrices is given and compared. Excellent fits have been obtained with a new phase-shift code ONEZERO, which is capable of taking into account all degrees of freedom in strong interactions. The Argand-plot method has been used for resonance analysis of the excited ⁶Li system. Five new broad T = 0 resonances above 15 MeV deuteron energy have been found in ⁶Li, corresponding to D₃, F₂, F₃, G₃ and G₄ resonant states. Problems from phase-shift ambiguities are pointed out.
Explanation of the backangle anomaly and the isotope effect within a microscopic study of elastic α-scattering on the even Ca isotopes
1982, Nuclear Physics, Section A
Elastic α-scattering on the isotopes ^40,42,44,48Ca has been studied microscopically within the framework of the generator coordinate method. For energies above the Coulomb barrier the backangle enhancement of the cross section in elastic α-⁴⁰Ca scattering is explained by several overlapping barrier resonances, while for energies below the barrier the backangle rise is caused by individual long-living resonances which — in agreement with recent experimental data — confirm the concept of an “α-⁴⁰Ca quasimolecule”. The isotope effect showing up in a different behaviour of the cross section at backangles is due to a different absorptive strength of the isotopes. “Neutron blocking” has been ruled out as a possible explanation of the isotope effect.
Explanation of the anomalously small absorption of α-particles in 40Ca nuclei
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Identification of quasimolecular resonances in low energy α-40Ca scattering and effects of compound nucleus excitation
1983, Nuclear Physics, Section A
Measurements of high resolution excitation functions for elastic ⁴⁰Ca(α, α) scattering between E_lab = 4.4 MeV and E_lab = 9.12 MeV have been performed in 4 keV steps. Significant deviations from pure compound elastic fluctuations were observed and were shown to be due to intermediate structures. By different methods of analysis four of these structures have been identified as intermediate resonances with spins and total widths as follows: E_lab = 6.67 MeV (J^π = 0⁺, Γ = 550 keV), E_lab = 7.22 MeV (J^π = 1⁻, Γ = 40 keV), E_lab = 7.75 MeV (J^π = 2⁺, Γ = 300 keV) and E_lab = 8.41 MeV (J_π = 3⁻, Γ = 220 keV). In addition, the data around 9 MeV indicate the existence of a 4⁺ resonance. The resonances are found to form a rotational band and support the picture of an α-⁴⁰Ca quasimolecule in remarkable agreement with microscopic calculations. Additional data for ³⁹K, ⁴¹Ca and ⁴⁸Ca do not show any indication for intermediate resonances. This is explained by the strong influence of cluster structures on the absorption process. The relation between the identified resonances and the “anomalous” α-scattering at higher energies is discussed in connection with microscopic calculations and simple local potential analyses.
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Nuclear Physics A

Abstract

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Cited by (9)

Phase-shift analysis of d-α elastic scattering between 3 and 43 MeV

Explanation of the backangle anomaly and the isotope effect within a microscopic study of elastic α-scattering on the even Ca isotopes

Explanation of the anomalously small absorption of α-particles in <sup>40</sup>Ca nuclei

Identification of quasimolecular resonances in low energy α-<sup>40</sup>Ca scattering and effects of compound nucleus excitation

Existence of core excited <sup>8</sup>Be = α + α cluster structure in α + α scattering

Resonances in low energy elastic scattering of α-particles from<sup>28</sup>Si