Coulomb Disintegration ofLi6

Abstract

The disintegration of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ projectiles into alpha particles and deuterons in the Coulomb field of a heavy target nucleus is studied theoretically by use of refined cluster model wave functions. Transitions to the assumed ${}_{}{}^3{}_{}{}^{}D$ states in ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, followed by alpha-deuteron breakup, as well as transitions to the alpha-deuteron continuum, are considered. A semiclassical, first-order time-dependent perturbation treatment is used. A very good agreement with measurements of the total breakup cross section with a gold target is obtained for bombarding energies below the Coulomb barrier. The long-range term in the relative-motion part of the cluster wave function is shown to be decisive for the magnitude of the breakup probability. No fitting of the nuclear model parameters is performed. The quadrupole transitions to the $3^{+}$ state at 2.18 MeV are found to be dominating for sub-barrier energies. The theoretical value of the reduced matrix element for excitations to this state is calculated to be $B(E2; 1\to 3)=85\times {10}^{-52\mathrm{}}{e}^2$ ${\mathrm{cm}}^4$. This value is about 20 times the single-particle estimate, but is consistent with the alpha-deuteron disintegration experiments. This large number is interpreted as originating from the large diffuseness of the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ nucleus.