Measurement of spin versus total kinetic energy of Ba 144 produced in spontaneous fission of Cf 252

Le résumé fourni par la source

We measure the average spin of $^{144}\mathrm{Ba}$, a common fragment produced in $^{252}\mathrm{Cf}$(sf), as a function of the total kinetic energy (TKE). We combine a twin Frisch-gridded ionization chamber with a world-class $\ensuremath{\gamma}$-ray spectrometer that was designed to measure high-multiplicity $\ensuremath{\gamma}$-ray events, Gammasphere. The chamber, loaded with a $^{252}\mathrm{Cf}$(sf) source, provides a fission trigger, the TKE of the fragments, the approximate fragment masses, and the polar angle of the fission axis. Gammasphere provides the total $\ensuremath{\gamma}$-ray yield, fragment identification through the tagging of decay $\ensuremath{\gamma}$ rays, and the feeding of rotational bands in the fragments. We determine the dependence of the average spin of $^{144}\mathrm{Ba}$ on the fragments' TKE by correlating the fragment properties with the distribution of discrete levels that are fed. We find that the average spin only changes by about $0.5\phantom{\rule{4pt}{0ex}}\ensuremath{\hbar}$ across the TKE range of 158--203 MeV. The virtual independence of the spin on TKE suggests that spin is not solely generated through the statistical excitation of rotational modes, and more complex mechanisms are required.

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