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), for 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 spectrometric techniques. From the isomeric yield ratios, fragment angular momenta (J(rms)) 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 Cf-249(n(th), 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 J(rms) has a nearly inverse correlation with elemental yield in fissioning systems from Th-230* to Cf-252 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 Th-230* to Cf-250* and Cf-252, the odd-even fluctuation on fragment J(rms) 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.