Gamma ray and internal conversion electron spectroscopy study of ¹⁵⁶Pm

The study of isotopes in the rare-earth region can help understand the evolution of nuclear shapes with increasing neutron number. This region is also of interest to nuclear astrophysics due to the presence of a peak abundance around A ∼160 in the nucleosynthesis of rare-earth elements. Furthermore, the existence of isomers in this region may affect the production rate of elements by slowing or accelerating their nucleosynthesis in the r-process environment. In this context, the ¹⁵⁶Pm isotope was previously identified and partially studied in various beta-decay and fission reaction experiments. However, an expanded level scheme and a measurement of its low-lying long-lived isomeric state half-life were missing. Therefore, an experiment has been conducted at the ATLAS/CARIBU facility at Argonne National Laboratory to study the beta-decay properties of the deformed odd-odd nucleus ¹⁵⁶Pm. The LSU-Argonne Conversion Electron Spectrometer (LACES) coupled to the X-Array/Scintillator and Tape Using Radioactive Nuclei (SATURN) decay station was employed to make simultaneous measurements of conversion electrons and gamma-rays. This setup yielded a precise measurement of the half-life of the low-spin K^π = 1⁺ isomeric state at 150.3 keV. An expanded level scheme with the transition multipolarity assignments based on internal conversion coefficients will also be presented.