Anomalous neutron yields confirmed for Ba-Mo and newly observed for Ce-Zr from spontaneous fission of Cf-252

摘要

We reinvestigated the neutron multiplicity yields of Ba-Mo, Ce-Zr, Te-Pd, and Nd-Sr from the spontaneous fission of Cf-252 by (i) using both gamma-gamma-gamma-gamma and gamma-gamma-gamma coincidence data, (ii) using up to date level scheme structures, and (iii) crosschecking analogous energy transitions in multiple isotopes, we have achieved higher precision than previous analyses. Particular attention was given to the Ba-Mo pairs where our results clearly confirm that the Ba-Mo yield data have a second hot fission mode where 8-10, and now 11 neutron evaporation channels are observed. These are the first observations of the 11 neutron channel. These 8-11 neutron channels are observed for the first time in the Ce-Zr pairs, but are not observed in other fission pairs. The measured intensities of the second mode in Ba-Mo and Ce-Zr pairs are similar to 1.5(4)% and similar to 1.0(3)%, respectively. These high neutron number evaporation modes can be an indication of hyperdeformation and/or octupole deformation in Ba143-145 and in Ce-146,Ce-148 at scission to give rise to such high neutron multiplicities.