Excitation of giant resonances in the Ca40(e,e’n)39Ca reaction

Decay neutrons from the Ca-40(e,e'n)Ca-39 reaction were studied in the giant resonance region. The cross sections and angular distributions, separated for n0 and n1 decays, were obtained for excitation energies between 19 and 27 MeV, at the effective momentum transfer of 0.35 fm-1. Legendre polynomial coefficients obtained from fitting the data are compared with those from the (e,e'p) reaction. In the energy range 19-21 MeV, the interference coefficients b1 and b3 for the ground state transition are in agreement, but the noninterference coefficient b2 is different. The different behavior of the angular distribution for protons and neutrons may suggest the interference of the decay from a T = 0 quadrupole resonance and the T = 1 giant dipole resonance. A similar tendency was also seen in comparing with the (e, e'p1) reaction. The Legendre polynomial coefficients for the no decay in the (e,e'n) reaction, transformed to the photon point, agree well with those of the (gamma,n0) reaction. The reduced total cross section is-consistent between the (e,e'n) and (gamma,n) reactions, but the cross section for (e,e'n0) is larger than that of (gamma,n0) near the peak of the resonance. The values of the longitudinal-transverse interference term are close to zero in the present region, which is rather small compared with the value near the resonance of the (e,e'p) reaction.