Systematics of fragment angular momentum in low-energy fission of actinides

Abstract

Independent isomeric yield ratios for 128Sb, 130Sb, 132Sb, 131Te, 133Te, 132I, 134I, 136I, 135Xe and 138Cs in 229Th(nth, f), for 136I in 233U(nth, f) and 239Pu(nth, f), for 138Cs in 235U(nth, f), for 130Sb, 136I and 135Xe in 241Pu(nth, f), for 128Sb, 130Sb, 130Sb, 132Sb, 131Te, 133Te, 134I, 136I, 135Xe and 138Cs in 245Cm(nth, f) and for 128Sb, 130Sb, 132Sb, 136I and 135Xe in 252Cf(S.F.) have been determined using radiochemical and gamma-ray spectrometric techniques. From the isomeric yield ratios, fragment angular momenta (Jrms) have been deduced using spin-dependent statistical-model analysis. These data along with the literature data in the above fissioning systems as well as in 249Cf(nth, f) show several important features. These features are: (i) Angular momenta for fragments with spherical 50-proton shell, 82-neutron shell and even-Z products are lower compared to the fragments with deformed 88-neutron shell, no shells and odd-Z products indicating the nuclear-structure effects. (ii) Fission fragment Jrms has a nearly inverse correlation with elemental yield in fissioning systems from 230Th∗ to 252Cf possibly due to coupling between the collective and intrinsic degrees of freedom. (iii) Although the percentage odd-even effect in the elemental yield decreases from 230Th∗ to 250Cf∗ and 252Cf, the odd-even fluctuation on fragment Jrms remains nearly the same in spite of the inverse correlation. This possibly indicates the effect of fragment deformation. (iv) Fission-product elemental yield as well as angular momentum have no definite correlation with fissionability since both are decided near the scission point.