Angular momentum of fission fragments in low energy fission of actinides

Abstract

Independent isomeric yield ratios (IYR) of $^{128}\mathrm{Sb}$, $^{130}\mathrm{Sb}$, $^{132}\mathrm{Sb}$, $^{131}\mathrm{Te}$, $^{133}\mathrm{Te}$, $^{132}\mathrm{I}$, $^{134}\mathrm{I}$, $^{136}\mathrm{I}$, $^{135}\mathrm{Xe}$, and $^{138}\mathrm{Cs}$ have been determined in fast neutron induced fission of $^{232}\mathrm{Th}$, $^{238}\mathrm{U}$, $^{240}\mathrm{Pu}$, and $^{244}\mathrm{Cm}$ as well as in thermal neutron induced fission of $^{232}\mathrm{U}$ and $^{238}\mathrm{Pu}$ using radiochemical and offline $\ensuremath{\gamma}$-ray spectrometric techniques. From the IYR, fragment angular momenta (${J}_{\mathrm{rms}}$) have been deduced using a spin-dependent statistical model analysis. These data along with the literature data for ${^{230}\mathrm{Th}}^{\ensuremath{\ast}}$, ${^{234}\mathrm{U}}^{\ensuremath{\ast}}$, ${^{236}\mathrm{U}}^{\ensuremath{\ast}}$, ${^{240}\mathrm{Pu}}^{\ensuremath{\ast}}$, ${^{242}\mathrm{Pu}}^{\ensuremath{\ast}}$, $^{244}\mathrm{Cm}$(SF), ${^{246}\mathrm{Cm}}^{\ensuremath{\ast}}$, ${^{250}\mathrm{Cf}}^{\ensuremath{\ast}}$, and $^{252}\mathrm{Cf}$(SF) for fifteen even-$Z$ fissioning systems show the following important features: (i) The ${J}_{\mathrm{rms}}$ 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 ${J}_{\mathrm{rms}}$ increase with ${Z}_{F}^{2}/{A}_{F}$. (ii) The ${J}_{\mathrm{rms}}$ 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 ${J}_{\mathrm{rms}}$ 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 ${J}_{\mathrm{rms}}$ values show an anticorrelation with the elemental yields. (v) The odd-even fluctuation on ${J}_{\mathrm{rms}}$ does not change drastically from Th to Cf, unlike the proton odd-even effect (${\ensuremath{\delta}}_{p}$) which decreases significantly with the increase of Coulomb parameter (${Z}_{F}^{2}/{A}_{F}^{1/3}$).