Fine structure in the $\hat{I}\pm$ decay of ${}^{223}$U

Abstract

Fine structure in the $\hat{I}\pm$ decay of ${}^{223}$U was observed in the fusion-evaporation reaction ${}^{187}$Re(${}^{40}$Ar, p3n) by using fast digital pulse processing technique. Two $\hat{I}\pm$-decay branches of ${}^{223}$U feeding the ground state and 244 keV excited state of ${}^{219}$Th were identified by establishing the decay chain ${}^{223}$U $\stackrel{\hat{I}{\pm }_1}{\to }$ ${}^{219}$Th $\stackrel{\hat{I}{\pm }_2}{\to }$ ${}^{215}$Ra $\stackrel{\hat{I}{\pm }_3}{\to }$ ${}^{211}$Rn. The $\hat{I}\pm$-particle energy for the ground-state to ground-state transition of ${}^{223}$U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62${}_{-10}^{+14}$ $\hat{I}¼$s. Evolution of nuclear structure for $N$ = 131 even-$Z$ isotones from Po to U was discussed in the frameworks of nuclear mass and reduced $\hat{I}\pm$-decay width, a weakening octupole deformation in the ground state of ${}^{223}$U relative to its lighter isotones ${}^{219}$Ra and ${}^{221}$Th was suggested.

6 pages, 6 figures