STUDY OF ISOMERIC CROSS-SECTION RATIO AND PRE-EQUILIBRIUM FRACTION IN PROTON AND ALPHA PARTICLE INDUCED NUCLEAR REACTIONS ON 197Au

Abstract

Excitation functions for the reactions 197 Au(p,n) 197g Hg and 197 Au(p,n) 197m Hg have been measured over the energy ranges from threshold up to 20 MeV using stacked foil activation technique. The isomeric cross-section ratio σm/(σm+σg) for the formation of 197g, m Hg was determined. The excitation functions and isomeric cross-section ratios were calculated for the reactions 197 Au(p,n) 197g,m Hg , 197 Au(p,2n) 196 Hg , 197 Au(p,3n) 195g,m Hg , 197 Au(p,4n) 194 Hg , 197 Au(p,5n) 193g,m Hg , 197 Au (α, n )200 Tl , 197 Au (α, 2n )199 Tl , 197 Au (α, 3n )198g,m Tl , 197 Au (α, 4n )197 Tl and 197 Au (α, 5n )196g,m Tl from reaction threshold up to 40 MeV for proton induced reactions and 80 MeV for alpha induced reactions. The results were compared with the theoretical cross-sections calculated by means of the code EMPIRE-II and with the available literature data, which makes use of the Hauser Feshbach model for the compound nuclear calculations and the exciton model for the pre-equilibrium emission part. The isomeric cross-section ratio is found to depend strongly on the relative spins of the isomeric and ground state, energy difference between the levels, presence of intermediate states and some dependence on decay modes and on the onset of pre-equilibrium emission.