”Extreme” γ-ray spectroscopy: single-neutron states in [sup 101]Sn and rotation of the proton emitter [sup 145]Tm

Abstract

In‐beam γ‐ray studies of nuclei with a large proton excess are faced with ever decreasing cross sections and large backgrounds due to strong less exotic reaction channels. However, many of the nuclei along the proton drip line α decay, proton decay or emit β‐delayed particles. This offers a very selective tag for prompt γ rays and has been known as the Recoil‐Decay Tagging (RDT) method. RDT has been extensively used with the Gammasphere array of Compton suppressed Ge detectors coupled with the Argonne Fragment Mass Analyzer. Recently, despite a very small cross section of about 50 nb and a long half life of ∼2 s, protons emitted following the β decay of 101Sn were used to identify γ‐ray transitions in 101Sn. As a result, the energy splitting between the neutron g7/2 and d5/2 orbitals outside the 100Sn core was deduced. The structure of light Sn isotopes is discussed in the framework of the shell model in light of the new results. Another state‐of‐the‐art example is the observation of a rotational ground‐state band in the fast proton emitter 145Tm, which decays with a half live of only ∼3 μs. In this experiment, coincidences between the proton decay to the 2+ excited state in the daughter nucleus and the 2+→0+ γ‐ray transition were also measured, which constitutes the first direct proof of proton decay fine structure. Based on the data the possibility of a triaxial shape in 145Tm is considered.