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, 233}Th ^* , ^{233, 234, 236, 239}U ^* , ^{239, 240, 241, 242}Pu ^* , ²⁴⁴Cm(SF), ^{245, 246}Cm ^* , 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.