SHELL AND ODD-EVEN EFFECTS IN PREEQUILIBRIUM NUCLEON EMISSIONS IN THE CONTINUUM FROM NUCLEON-INDUCED REACTIONS
Department of Nuclear Engineering, Kyushu University, Fukuoka 812, Japan
We have investigated the shell and odd-even effects in preequilibrium particle emissions in the continuum from (p,p'), (n,n'), (p,n), and (n,p) reactions. Double differential cross sections were measured for 18-MeV (p,xp) reactions on 90Zr, 93Nb, 92,94,96,98,100Mo, 106Pd, and Ag, and for 14.1-MeV (n,xn) reactions on Ag, Cd, In, Sn, Sb, and Te. The shell and odd-even effects were not appreciably observed in the preequilibrium (p,p') and (n,n') spectra in excitation energies above 4 MeV. This was reasonably interpreted on the basis of the state densities generated from the Nilsson model and the modified uniform spacing (MUS) model. Neutron energy spectra from 25-MeV (p,n) reactions on nuclei in the Zr-Mo and Cr-Ni regions were analyzed in terms of the exciton model in which the effective Q value and the state densities generated from the MUS model were employed and the pairing correlation was taken into account. The calculated spectra showed good agreement with not only the experimental ones in the continuum region of 12-18 MeV, but also those with pronounced structures above 18 MeV. The same model was also applied to the analyses of 18-MeV (p,n) reactions and 14-MeV (n,p) reactions.
KEYWORDS: nucleon induced reaction, preequilibrium process, shell and odd-even effects, state density, effective Q value