| dc.description.abstract | High spin states of the neutron-rich $^{104}$Mo nucleus have been reinvestigated by analyzing the $\gamma$-rays in the spontaneous fission of $^{252}$Cf with Gammasphere. Both $\gamma$-$\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$-$\gamma$ coincidence data were analyzed. A new $\Delta$I=1 band has been discovered with a tentative 5$^-$ band-head, and is proposed to form a class of chiral vibrational doublets with another 4$^-$ band previously found. A new 6$^+$ band is proposed to be the $\gamma\gamma\gamma$ band. The levels of the 4$^-$ and 5$^-$ chiral doublets in $^{106}$Mo have been reassigned. Angular correlation measurements have been performed to determine the spins and parities. The origin of the chiral doublet bands in $^{104, 106}$Mo are interpreted as a neutron h$_{11/2}$ particle and mixed (d$_{5/2}$, g$_{7/2}$) hole coupled to the short and long axis, respectively. New side bands have been observed in $^{106}$Mo. PES calculations have been performed to determine the configurations of the side bands. TPSM calculations have been performed for the chiral doublet bands in $^{104,106}$Mo. The results show reasonably good agreement with the experimental data.
Furthermore, neutron multiplicity yields of Ba-Mo, Ce-Zr, Te-Pd, Xe-Ru and Nd-Sr from the spontaneous fission of $^{252}$Cf have been reinvestigated; by (i) using both $\gamma$-$\gamma$-$\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$ coincidence data, (ii) using up to date level scheme structures, and (iii) cross-checking analogous energy transitions in multiple isotopes, so 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, 9, 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 have not been observed in other fission pairs. The measured intensities of the second mode in Ba-Mo and Ce-Zr pairs are $\sim$1.5(4)$\%$ and $\sim$1.0(3)$\%$, respectively. These high neutron number evaporation modes can be an indication of hyperdeformation and/or octupole deformation in $^{143-145}$Ba and in $^{146,148}$Ce at scission to give rise to such high neutron multiplicities. | |
