Angular momentum of fission fragments in low energy fission of actinides

Independent isomeric yield ratios (IYR) of ¹²⁸Sb, ¹³⁰Sb, ¹³²Sb, ¹³¹Te, ¹³³Te, ¹³²I, ¹³⁴I, ¹³⁶I, ¹³⁵Xe, and ¹³⁸Cs have been determined in fast neutron induced fission of ²³²Th, ²³⁸U, ²⁴⁰Pu, and ²⁴⁴Cm as well as in thermal neutron induced fission of ²³²U and ²³⁸Pu using radiochemical and offline γ-ray spectrometric techniques. From the IYR, fragment angular momenta (Jᵣₘₛ) have been deduced using a spin-dependent statistical model analysis. These data along with the literature data for ²³⁰Th^, ²³⁴U^, ²³⁶U^, ²⁴⁰Pu^, ²⁴²Pu^, ²⁴⁴Cm(SF), ²⁴⁶Cm^, ²⁵⁰Cf^, and ²⁵²Cf(SF) for fifteen even-Z fissioning systems show the following important features: (i) The Jᵣₘₛ of the odd-Z fission products are higher than those of the even-Z fission products, indicating the odd-even effect. For both the odd-Z and even-Z fission products, the Jᵣₘₛ increase with ZF²/AF. (ii) The Jᵣₘₛ of fragments with spherical 50-p and 82-n shells are lower compared to those of fragments outside the spherical shell, indicating the effect of shell closure proximity. (iii) The Jᵣₘₛ of the fission products increase with mass number in spite of fluctuations in shell closure proximity and odd-even effects but do not show any correlation with the neutron emission curve. (iv) In all fifteen even-Z fissioning systems from Th to Cf, the yield-weighted Jᵣₘₛ values show an anticorrelation with the elemental yields. (v) The odd-even fluctuation on Jᵣₘₛ does not change drastically from Th to Cf, unlike the proton odd-even effect (δₚ) which decreases significantly with the increase of Coulomb parameter (ZF²/AF1/3).