Determine the excitation energy of the isomer in 154Pm

Determine the excitation energy of the reported isomeric state in promethium-154, which remains unknown, to clarify its impact on mass measurements and comparisons with β-endpoint determinations.

Background

In the A/q = 77.0 series, an isomeric state in 154Pm is known, but its excitation energy has not been measured. The measured mass excess for 154Pm shows a lighter mass compared with a literature value inferred from a β-endpoint measurement of 154Nd → 154Pm, complicating interpretation.

An accurate determination of the isomer’s excitation energy is necessary to ensure consistent mass evaluations and resolve differences with indirect β-endpoint results.