Direct observation of long-lived isomers in 212Bi

Area of Science:

• Nuclear Physics
• Atomic Physics

Background:

• Long-lived isomers in Bismuth-212 (212Bi) are nuclear states with significant implications for nuclear structure and decay studies.
• Previous measurements of the second isomer's energy and half-life in 212Bi were limited, necessitating further investigation.

Purpose of the Study:

• To investigate the properties of long-lived isomers in 212Bi.
• To accurately determine the excitation energy and half-life of the second isomer in 212Bi.
• To understand the discrepancies observed in previous measurements.

Main Methods:

• Studying 212Bi isomers produced via Uranium-238 (238U) projectile fragmentation at 670 MeV per nucleon.
• Injecting highly charged ions into a storage ring to measure masses and half-lives.
• Comparing experimental data with shell-model calculations.

Main Results:

• Confirmed the excitation energy of the first isomer of 212Bi.
• Observed the second isomer at 1478(30) keV, differing from the previous >1910 keV value.
• Measured an extended Lorentz-corrected in-ring half-life of >30 min for the second isomer, significantly longer than the 7.0(3) min for the neutral atom.
• Identified a substantial internal decay branch for neutral atoms as the cause for energy and half-life differences.

Conclusions:

• The observed energy and half-life differences are explained by an unrecognized internal decay branch in neutral 212Bi atoms.
• Shell-model calculations show good agreement with the determined isomer excitation energy.
• New calculations predict states that could aid future isomer deexcitation studies.