Single and pair neutron transfers at sub-barrier energies

Abstract

Multinucleon transfer cross sections in the ${}^{96}$Zr+${}^{40}$Ca system have been measured, in inverse kinematics, at bombarding energies ranging from the Coulomb barrier to $\ensuremath{\sim}$25$%$ below. Targetlike recoils have been identified in A, Z and velocity with the large solid angle magnetic spectrometer PRISMA. The experimental data for one- and two-neutron transfer channels have been compared with semiclassical microscopic calculations. For the two-neutron transfer channels the relevance of the transitions to the ground state and to the 0${}^{+}$ excited states of ${}^{42}$Ca are discussed by employing, for the reaction mechanism, the successive approximation. It is found that the transition to the 0${}^{+}$ state at $\ensuremath{\sim}$6 MeV, whose wave function is dominated by the two neutrons in the $2{p}_{3/2}$ shell, is much larger than the ground state one. The comparison with the inclusive data reveals that transitions to states with high multipolarity and non-natural parity are important. This suggests that more complex two-particle correlations have to be incorporated in the treatment of the transfer process.