Microscopic calculation of proton and alpha-particle inelastic scattering to study the excited states of ${}^6$He and ${}^8$He

Abstract

Elastic and inelastic cross sections of the $p+{}^6\text{He}$, $p+{}^8\text{He}$, and $\alpha +{}^8\text{He}$ reactions were investigated using the Melbourne $g$-matrix folding approach with the theoretical densities of ${}^6\text{He}$ and ${}^8\text{He}$ obtained by a microscopic structure model of antisymmetrized molecular dynamics (AMD). Microscopic coupled-channel (MCC) calculations of the $p+{}^6\text{He}$ and $p+{}^8\text{He}$ reactions were performed to investigate transition properties of the ${}^6\text{He}(2_1^{+})$ and ${}^8\text{He}(2_1^{+})$ states. The MCC+AMD calculations reproduced elastic cross sections of the $p+{}^6\text{He}$ reaction at $E=40.9$ MeV/A and of the $p+{}^8\text{He}$ reaction at $E=32.5$ and 72 MeV/A, which have both been measured by inverse kinematics experiments. For $p+{}^6\text{He}$ inelastic scattering to the $2_1^{+}$ state, the calculated result was in reasonable agreement with the $(p,p^{\prime })$ data at $E=24.5$ and 40.9 MeV/A and supported the AMD prediction of the neutron transition matrix element $M_n=7.9$ fm${}^2$. For the $p+{}^8\text{He}$ inelastic scattering to ${}^8\text{He}(2_1^{+})$, the MCC+AMD calculation overshot the $(p,p^{\prime })$ cross sections at $E=72$ MeV/A by a factor of three. According to a phenomenological model analysis, $M_n$ values in the range of 4--6 fm${}^2$ were favored to reproduce the ${}^8\text{He}(2_1^{+})$ cross sections of the $p+{}^8\text{He}$ reaction at $E=72$ MeV/A. For the $\alpha +{}^8\text{He}$ reaction, the MCC+AMD calculation reproduced the elastic cross sections at $E=26$ MeV/A. Theoretical predictions of the ($p,p^{\prime }$) and ($\alpha ,{\alpha }^{\prime }$) cross sections to the ${}^8\text{He}(0_2^{+})$, ${}^8\text{He}(1_1^{-})$, ${}^8\text{He}(2_3^{+})$ and ${}^8\text{He}(3_1^{-})$ states are also given.

Comments: 12 pages, 12 figures