EXCITATION-FUNCTIONS AND ISOMERIC CROSS-SECTION RATIOS OF THE CU-63(N,ALPHA) CO-60(M,G), CU-65(N,ALPHA) CO-62(M,G), AND NI-60(N,P) CO-60(M,G) PROCESSES FROM 6 TO 15 MEV

Excitation functions were measured for the Cu-63(n,alpha)Co-60m, Cu-65(n,alpha)Co-62m, and Cu-65(n,alpha)Co-62g reactions over the neutron energy range of 6.3 to 14.8 MeV. Use was made of the activation technique in combination with high-resolution gamma-ray spectroscopy. The neutrons were produced via the H-2(d,n)He-3 reaction using a deuterium gas target at a variable energy compact cyclotron (E(n) = 6.3-11.9 MeV) and via the H-3(d,n)He-4 reaction using a solid Ti-T target at a neutron generator (E(n) = 13.7-14.8 MeV). From the available experimental data isomeric cross section ratios were determined for the isomeric pair Co-60m,g in Cu-63 Cu(n,alpha) and Ni-60(n,p) reactions, and for the pair Co-62m,g in the Cu-65(n,alpha) reaction. Statistical model calculations taking into account precompound effects were performed for the formation of both the isomeric and ground states of the products. The calculational results on the total (n, p) and (n, alpha) cross sections agree well with the experimental data; in the case of isomeric states, however, some deviations occur. The experimental isomeric cross section ratios are reproduced only approximately by the calculation; at 15 MeV the spin distribution of the level density has a significant effect on the calculation. For low-lying levels the isomeric cross section ratio depends strongly on the spins of the levels involved and not on their excitation energies. At a given neutron energy the population of the higher spin isomer appears to be higher in the (n, alpha) process than in the (n, p) reaction.