Nuclear transparency and the onset of strong absorption regime in the12C+24Mgsystem

Abstract

The elastic scattering of 12 C + 24 M g has been studied by means of a phaseshift analysis of 21 angular distributions ranging from E lab = 16 MeV up to E lab = 40 MeV. A tri-dimensional plot of the reflection coefficient of the Smatrix as a function of the angular momentum and the energy shows a well defined region of energy, which separates two regimes: strong absorption for higher energies and the so called "anomalous transparency regime", recently observed in this system at low energies. The Argand diagrams of the S-matrix in angular momentum space also present very contrasting behaviours in the two regions with very rapidly varying phases in the low energy region, which we associate with a parity dependent term in the S-matrix directly related to significant coupling to the elastic transfer of a 12 C nucleus. An anomalous transparency has been observed[1] in the12 C + 24 Mg system at energies around and slightly above the Coulomb barrier (E ≤ 1.5E b ). The angular distributions of the elastic scattering are characterized by oscillations and require a very small imaginary part in the optical potential in order to be fitted. These oscillations are present in practically the whole angular distribution, even at forward and intermediate angles, in contrast to the well-known phenomenon of Anomalous Large Angle Scattering (ALAS), which is observed at slightly higher energies (E ≥ 2.5E b ) and is characterized by oscillating angular distributions and excitation functions at large angles [2]. The oscillations observed in the angular distributions of the systems which exhibit ALAS phenomenon can be reproduced by a background strong absorption S-matrix plus a localized perturbation normally around the grazing angular 1

Elastic scattering analysis of $^{12}$C+$^{24}$Mg by WKB method

“…Sciani et al use a shallow and energy-dependent potential parameter and investigate the elastic and inelastic scattering data of the 12 C+ 24 Mg system by optical and coupled channels methods [1]. Lichtenthäler et al examine elastic scattering data of this system by parametrized phase shift method [2]. Boztosun et al propose a new coupling potential, which has attractive and repulsive terms as distinct from the standard model, in order to explain the elastic and inelastic scattering data of the 12 C+ 24 Mg system, simultaneously [3][4][5].…”