Abstract
Solenogam is a recoil spectrometer designed and constructed for use at the Australian National University (ANU) Heavy-Ion Accelerator Facility (HIAF). The design enables the study of nuclear excitations populated by the decay of long-lived states such as isomers and radioactive ground states. Solenogam is comprised of high-sensitivity γ -ray and electron detector arrays coupled to a new 8-T solenoid. While the installation of the 8-T solenoid proceeds, off-line measurements have been made to characterise Solenogam’s performance. Gamma-electron coincidences in the electron capture decay of 182 Re into 182 W were used to investigate conversion coeffcients and γ -e – angular correlations. The measured conversion coeffcients show good agreement with theoretical calculations and have been used to extract E 0/ E 2 mixing ratios for a number of J → J transitions. The angular correlations measured by the array are in qualitative agreement with theoretical calculations. However, the magnitudes of the correlations are attenuated by approximately 40% for reasons unknown at present. These results are the first full use of the Solenogam system for γ -e – coincidence measurements and have proven that the system is capable of highly-sensitive internal conversion analysis of complex decays.
Highlights
Shape coexistence is a phenomenon observed in nuclei near closed proton and mid neutron shells (e.g Z ∼ 82, N ∼ 104)
This was subsequently increased to three high purity germanium (HPGe) and one low energy photon spectrometer (LEPS) detector for the second measurement
The Solenogam array was used to measure conversion coefficients using γ-e− coincidences for a range of transitions in 182W and good agreement was achieved with theoretical values
Summary
Shape coexistence is a phenomenon observed in nuclei near closed proton and mid neutron shells (e.g Z ∼ 82, N ∼ 104). One characteristic of coexisting shapes is the presence of multiple rotational bands with different energy spacings dependent on the moment of inertia Transitions between these rotational structures with J → J spin changes are important as they proceed via E0, M1 and E2 components, whose strengths depend strongly on the wavefunctions (and shapes) of the initial and final states. The first used the Si(Li) array coupled with two high purity germanium (HPGe) gamma-ray detectors. This was subsequently increased to three HPGe and one low energy photon spectrometer (LEPS) detector for the second measurement. It should be noted that the third HPGe detector had a non-standard placement in the array and was located at θ ≈ 45° and φ = 90° In both measurements, one of the HPGe detectors was Compton suppressed. Energy resolution in matrices that sum across all detectors are ≈ 3 keV (0.2%) for the HPGe detectors and ≈ 4 keV (0.4%) for the Si(Li) detectors for the 1408keV 152Eu decay line and corresponding K conversion line, respectively
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