Identification of isomeric states in the N=73 neutron-deficient nuclei 132 Pr and 130 La

Le résumé fourni par la source

Decays from isomeric states in the neutron-deficient $N=73$ nuclei ${}^{132}$Pr and ${}^{130}$La have been observed for the first time. Half-lives of 486(70) ns and 2.46(4) $\ensuremath{\mu}$s were measured for two isomeric states in ${}^{132}$Pr. The decay from the 486 ns $({8}^{\ensuremath{-}})$ isomer has been interpreted as a hindered $E1$ transition from the bandhead state of the excited $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{7/2}$ configuration. The decay from the 2.5 $\ensuremath{\mu}$s $({8}^{+})$ isomer is consistent with the Weisskopf estimate for a low-energy $E2$ transition. An analogous 0.74(3) $\ensuremath{\mu}$s decay from an $({8}^{+})$ isomer in the neighboring isotone ${}^{130}$La has also been observed which similarly can be explained if the transition has $E2$ character. The Weisskopf interpretation for the isomer hindrance is strengthened by the lack of evidence for shape or $K$ isomerism due to the $\ensuremath{\gamma}$-soft shapes predicted by configuration-constrained potential-energy-surface calculations.

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