# Fine structure in the $\alpha$ decay of $^{223}$U

## TL;DR

This study observed fine structure in the alpha decay of uranium-223, identifying decay branches and updating decay energy and half-life, while discussing nuclear structure evolution and deformation effects in isotones.

## Contribution

It reports the first observation of fine structure in $^{223}$U alpha decay, with precise energy and half-life measurements, and insights into nuclear shape evolution.

## Key findings

- Alpha decay branches to ground and excited states identified.
- Alpha particle energy for $^{223}$U decay measured at 8993 keV.
- Half-life of $^{223}$U updated to 62 microseconds.

## Abstract

Fine structure in the $\alpha$ decay of $^{223}$U was observed in the fusion-evaporation reaction $^{187}$Re($^{40}$Ar, p3n) by using fast digital pulse processing technique. Two $\alpha$-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 $\xrightarrow{\alpha_{1}}$ $^{219}$Th $\xrightarrow{\alpha_{2}}$ $^{215}$Ra $\xrightarrow{\alpha_{3}}$ $^{211}$Rn. The $\alpha$-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$^{+14}_{-10}$ $\mu$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 $\alpha$-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.