Direct observation of long-lived isomers in $^{212}$Bi

TL;DR

This study directly observed long-lived isomers in 212Bi using projectile fragmentation and storage ring techniques, revealing new energy levels and extended half-lives, and providing insights into their decay mechanisms.

Contribution

It provides the first direct observation of the second isomer in 212Bi and refines its excitation energy and half-life, challenging previous assumptions and supporting shell-model predictions.

Findings

Second isomer observed at 1478 keV with >30 min half-life

Confirmation of the first isomer's excitation energy

Discovery of a substantial internal decay branch in neutral atoms

Abstract

Long-lived isomers in 212Bi have been studied following 238U projectile fragmentation at 670 MeV per nucleon. The fragmentation products were injected as highly charged ions into the GSI storage ring, giving access to masses and half-lives. While the excitation energy of the first isomer of 212Bi was confirmed, the second isomer was observed at 1478(30) keV, in contrast to the previously accepted value of >1910 keV. It was also found to have an extended Lorentz-corrected in-ring halflife >30 min, compared to 7.0(3) min for the neutral atom. Both the energy and half-life differences can be understood as being due a substantial, though previously unrecognised, internal decay branch for neutral atoms. Earlier shell-model calculations are now found to give good agreement with the isomer excitation energy. Furthermore, these and new calculations predict the existence of states at slightly higher energy that could facilitate isomer de-excitation studies.