Coulomb polarizability of the deuteron and the E1 capture mechanism in the 4He(d, gamma )6Li reaction.

Abstract

The $^{4}\mathrm{He}$ (d,\ensuremath{\gamma}${)}^{6}$Li reaction, which proceeds through the overwhelming E2 transition, but with a small admixture of the E1 transition, is a possible mechanism for the $^{6}\mathrm{Li}$ nucleosynthesis in the Big Bang. The E1 radiation is, however, strongly suppressed in the radiative deuteron capture reaction in self-conjugate nuclei. Usually, the observed small, but not negligible, E1 radiation has been attributed to the spin-dependent electric dipole operator. In this study it is shown how the Coulomb polarization of the deuteron $^{4}\mathrm{He}$(d,\ensuremath{\gamma}${)}^{6}$Li reaction. Expressly we investigate the E1 capture process which proceeds with a small change of the deuteron internal structure in the entrance channel state. The structural change of the deuteron is engendered by the Coulomb field in the system of target and deuteron and such a deviant deuteron state is surveyed by calculating the expectation value of the relative coordinate between the proton and neutron in the deuteron. We then show how the electrically polarized deuteron state releases the usual E1 selection rule, and subsequently we calculate the relative intensity of the E1 versus E2 radiation in the $^{4}\mathrm{He}$(d,\ensuremath{\gamma}${)}^{6}$Li reaction.