SYSTEMATICS OF FRAGMENT ANGULAR-MOMENTUM IN LOW-ENERGY FISSION OF ACTINIDES

Independent isomeric yield ratios for Sb-128, Sb-130, Sb-132, Te-131, Te-133, I-132, I-134, I-136, Xe-135 and Cs-138 in Th-229(n(th), f), fo r I-136 in U-233(n(th), f) and Pu-239(n(th), f), for Cs-138 in U-235(n (th), f), for Sb-130, I-136 and Xe-135 in Pu-241(n(th), f) for Sb-128, Sb-130, Sb-132, Te-131, Te-133, I-134, I-136, Xe-135 and Cs-138 in Cm -245(n(th), f) and for Sb-128, Sb-130, Sb-132, I-136 and Xe-135 in Cf- 252(S.F.) have been determined using radiochemical and gamma-ray spect rometric techniques. From the isomeric yield ratios, fragment angular momenta (J(rms)) have been deduced using spin-dependent statistical-mo del analysis. These data along with the literature data in the above f issioning systems as well as in Cf-249(n(th), f) show several importan t features. These features are: (i) Angular momenta for fragments with spherical 50-proton shell, 82-neutron shell and even-Z products are l ower compared to the fragments with deformed 88-neutron shell, no shel ls and odd-Z products indicating the nuclear-structure effects. (ii) F ission fragment J(rms) has a nearly inverse correlation with elemental yield in fissioning systems from Th-230 to Cf-252 possibly due to co upling between the collective and intrinsic degrees of freedom. (iii) Although the percentage odd-even effect in the elemental yield decreas es from Th-230 to Cf-250* and Cf-252, the odd-even fluctuation on fra gment J(rms) remains nearly the same in spite of the inverse correlati on. This possibly indicates the effect of fragment deformation. (iv) F ission-product elemental yield as well as angular momentum have no def inite correlation with fissionability since both are decided near the scission point.