Single-particle spin effect on fission fragment angular momentum

Abstract

Independent isomeric yield ratios (IYR) of 128Sb, 130Sb, 132Sb, 131Te, 133Te, 132I, 134I, 136I, 135Xe, and 138Cs have been determined in the fast neutron-induced fission of 243Am using the radiochemical and γ-ray spectrometric technique. From the IYR, fragment angular momenta (J rms) have been deduced using the spin-dependent statistical model analysis. From the J rms-values and experimental kinetic energy data deformation parameters (β) have been deduced using the pre-scission bending mode oscillation model and the statistical model. The J rms- and β-values of fission fragments from the present and earlier work in the odd-Z fissioning systems ( 238Np * , 242Am * and 244Am * ) are compared with the literature data in the even-Z fissioning systems ( 230, 233Th * , 233, 234, 236, 239U * , 239, 240, 241, 242Pu * , 244Cm(SF), 245, 246Cm * , 250Cf * and 252Cf(SF)) to examine the role of single-particle (proton) spin effect. It was observed that i) in all the fissioning systems J rms- and β-values of the fragments with spherical 82n shell and even-Z products are lower than the fragments away from the spherical neutron shell and odd-Z products, which indicate the effect of nuclear structure. ii) For both even-Z and odd-Z fission products J rms-values increase with Z F 2/A F due to increase in Coulomb torque. iii) The J rms- and β-values of even-Z fission products are comparable in all the fissioning systems. However, for odd-Z fission products they are slightly higher in the odd-Z fissioning systems compared to their adjacent even-Z fissioning systems. This is possible due to the contribution of the extra single-particle (proton) spin of the odd-Z fissioning systems to their odd-Z fragments. iv) The yield-weighted fragment angular momentum and elemental yields profile shows an anti-correlation in even-Z fissioning systems but not in the odd-Z fissioning systems.