Measurement and analysis of the excitation function and isomeric cross section ratios forα-induced reaction on Ir, Au, Re and Ta nuclei

Abstract

Excitation functions and a few isomeric cross-section ratios for production of (1)192Au,193Au,194Au,195Au and192Ir nuclides inα-induced reactions on191,193Ir, (2)197Tl,197m Hg,198m,g Tl,199Tl and200Tl nuclides inα-induced reaction in197Au and (3)183Re and184m,g Re nuclides inα-induced reaction in181Ta and185Re are obtained from the measurements of the residual activities by the conventional stacked-foils technique from threshold to 50MeV. The excitation function and isomeric cross-section ratios for nuclear reaction181Ta(α,n)184m,g Re are compared with the theoretical calculation using the code Stapre which is based on exciton model for pre-equilibrium phase and Hauser-Feshbach formalism taking angular momentum and parity into account for the equilibrium phase of the nuclear reaction. All other experimental excitation functions are compared with the calculations considering equilibrium as well as pre-equilibrium reaction mechanism according to the geometry dependent hybrid (GDH) model and hybrid model of Blann using the code Alice/91. The high energy part of the excitation functions are dominated by pre-equilibrium reaction mechanism whereas the low energy parts are dominated by 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 precompound decay than for central collisions) compared to hybrid model. However in the energy range of present measurement most of the excitation functions are fitted reasonably well by both GDH model and hybrid model with initial exciton numberN 0=4(N n=2,N p=2,N h=0). Barring a few reactions we have found the overall agreement between theory and experiment is reasonably good taking the limitations of the theory into account.