MEASUREMENT AND ANALYSIS OF THE EXCITATION-FUNCTION AND ISOMERIC CROSS-SECTION RATIOS FOR ALPHA-INDUCED REACTION ON IR, AU, RE AND TA NUCLEI

Excitation functions and a few isomeric cross-section ratios for produ ction of (1) Au-192, Au-193, Au-194, Au-195 and Ir-192 nuclides in alp ha-induced reactions on Ir-191,Ir-193, (2) Tl-197, Hg-197m, Tl-198m,Tl -g, Tl-199 and Tl-200 nuclides in alpha-induced reaction in Au-197 and (3) Re-183 and Re-184m,Re-g nuclides in alpha-induced reaction in Ta- 181 and Re-185 are obtained from the measurements of the residual acti vities by the conventional stacked-foils technique from threshold to 5 0 MeV. The excitation function and isomeric cross-section ratios for n uclear reaction Ta-181(alpha, n)Re-184m,Re-g are compared with the the oretical calculation using the code Stapre which is based on exciton m odel for pre-equilibrium phase and Hauser-Feshbach formalism taking an gular momentum and parity into account for the equilibrium phase of th e nuclear reaction. All other experimental excitation functions are co mpared with the calculations considering equilibrium as well as pre-eq uilibrium reaction mechanism according to the geometry dependent hybri d (GDH) model and hybrid model of Blann using the code Alice/91. The h igh energy part of the excitation functions are dominated by pre-equil ibrium reaction mechanism whereas the low energy parts are dominated b y equilibrium evaporation with its characteristic peak. The GDH model provides a potentially better description of the physical process (i.e ., a higher probability for peripheral collisions to undergo precompou nd decay than for central collisions) compared to hybrid model. Howeve r in the energy range of present measurement most of the excitation fu nctions are fitted reasonably well by both GDH model and hybrid model with initial exciton number N-0 = 4(N-n = 2, N-p = 2, N-h = 0). Barrin g a few reactions we have found the overall agreement between theory a nd experiment is reasonably good taking the limitations of the theory into account.