Conversion Electrons in ^154,156Gd

One of the open questions of nuclear structure is the nature of excited 0+ states. Probing the 0+ states in nuclei requires spectroscopy of the 0+ states with respect to other states. One such probe is conversion electrons. The transitions between two 0+ states can only be seen via E0 transitions, which are forbidden via γ-rays. Further, E0 components of J^π → J^π transitions can give similar probes of relationships between bands. Information on E0 components are challenging to measure and sparse in nuclear databases.

The rare-earth region provides a rich landscape to probe pure and mixed E0 transitions. The deformed nature of nuclei in the area leads to a large number of nuclear structure phenomena. In ¹⁵⁴Gd, 16 0+ states have been seen in previous studies, the nature of many are unknown. The first excited 0+ state is of great interest, due to its large E0 strength to the ground state. There is a question of the nature of this state and its potential role as an example of β-vibration, or an indication of shape coexistence. ¹⁵⁶Gd is one of the most well-studied nuclei in the rare-earth region. It has a large number of known levels, lifetimes and mixing ratios, allowing for the study of mixed E0 transitions.

This work reports on results for transitions in ^154,156Gd following the ^152,154Sm(α,2n) reaction using the Internal Conversion Electron Ball (ICEBall) array in coincidence with γ-rays at the University of Notre Dame Nuclear Science Laboratory (NSL).

ICEBall was re-implemented at the NSL 8 years ago and the γ-rays were detected by GEORGINA, a HPGe array at the NSL, and Clovershare, segmented HPGe detectors purchased by the Yale Nuclear Structure Laboratory that are shared by a consortium of universities and laboratories for experimental campaigns. New J^π → J^π transitions where measured for both ^154,156Gd, allowing for the interpretation of excited band structures in the nuclei.