Nuclear-charge distribution forA=121from thermal-neutron-induced fission ofU235

The fractional cumulative yield of ${}_{}{}^{121}{}_{}{}^{}\mathrm{Ag}$ and the fractional independent yields of ${}_{}{}^{121}{}_{}{}^{}\mathrm{Cd}$, ${}_{}{}^{121}{}_{}{}^{}\mathrm{In}$, and ${}_{}{}^{121}{}_{}{}^{}\mathrm{Sn}$ from thermal-neutron-induced fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ were determined radiochemically to be 0.12±0.05, 0.61±0.09, 0.24±0.08, and 0.03±0.04, respectively. The yield values were used to determine the nuclear-charge-distribution parameters ${\sigma }_Z$=0.55±0.10 and ΔZ=0.50±0.05 for A=121. The ${\sigma }_Z$ for A=121 is close to ${\sigma }_Z$¯=0.52±0.02 for high-yield fission products, and no evidence for an even-odd Z effect was found for A=121. The positive ΔZ value, which corresponds to $Z_P$=48.15, is similar to those for several higher mass numbers reported previously, and it is considerably greater than the negative values predicted by the scission-point theoretical model. The use of a separation distance between nascent fragments greater than 1.4 fm, the value used in the theoretical calculations, could reduce the discrepancy and could also account for the observed enhanced independent yields of tin fission products with $Z_P$ near 50 (A=126–129).