Resonance effects in elastic and first excited level inelastic neutron scattering on 12C from 15.0 to 18.25 MeV

doi:10.1016/0375-9474(80)90401-7

Nuclear Physics A

Volume 344, Issue 3, 11 August 1980, Pages 446-474

https://doi.org/10.1016/0375-9474(80)90401-7 Get rights and content

Abstract

In order to investigate the reaction mechanisms for elastic and first excited level (I^π = 2⁺, E_x = 4.44 MeV) inelastic n-¹²C scattering, angular distributions of several observables have been measured: differential elastic cross sections at E_n = 15.0, 15.85 and 18.25 MeV, elastic polarizations at E_n = 15.85 MeV, differential inelastic cross sections and spin-flip probabilities at E_n = 15.0, 15.85, 16.9 and 18.25 MeV, and inelastic analyzing powers and spin-flip analyzing powers at E_n = 15.85 MeV. Neutron time-of-flight techniques with a scintillating scatterer have been used. Spin-flip data have been determined by means of the (n, n′γ ⊥) correlation. Detailed comparisons of the experimental results were made with the predictions of collective-model CC calculations using the full Thomas form for the deformed spin-orbit potential. Large and energy-dependent spin-orbit deformations (β₂^s.o. ≳ 3β₂^c) were needed indicating nuclear structure effects. The fit to the 15.85 MeV polarization data was considerably improved by adding $d_{32} and f_{52}$ Breit-Wigner resonance amplitudes to the optical-model amplitudes. Inelastic scattering data were analyzed in terms of a microscopic antisymmetrized DWA in which high-lying resonance states are incorporated explicitly as doorway states. Higher-order processes are described by the addition of a phenomenological imaginary part to the transition potential. These analyses reveal the presence of a quadrupole resonance at about 21 MeV excitation in ¹²C. The results are also influenced to a lesser extent by the El giant dipole resonance and a dipole resonance at E_x ≈ 19.5 MeV.

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^†: Present address: Institut für Plasmaforschung der Universität Stuttgart, 7000 Stuttgart 80, Fed. Rep. of Germany.

^††: Present address: Physikalisch-Technische Bundesanstalt, 3300 Braunschweig, Fed. Rep. of Germany.

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Nuclear Physics A

Abstract

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Analysis of neutron+nucleus scattering data with nonlocal optical potentials based on the resonating-group formulation

Analysing power for <sup>12</sup>C(n,n<inf>0,1</inf>)<sup>12</sup>C and evaluation of n-<sup>12</sup>C scattering at 18.2 MeV