Investigations of a=34 nuclei through fusion evaporation using the GALILEO spectrometer

The nuclear shell model has accurately predicted many experimental trends in the atomic mass region of A=20-60 and beyond. One way to examine this model is by studying mirror nuclei–which have exchanged numbers of protons and neutrons. Differences between the analogue nuclear energy levels and their decay patterns in mirror nuclei are key in quantifying isospin symmetry in the nuclear force. Of particular interest is studying the neutron deficient 34Ar and compare its structure to its mirror nucleus 34S. Whilst 34S has been extensively studied, 34Ar has only been studied at comparatively low energies. In addition, shell model calculations of mirror energies for A=34 Ar-Cl-S seem to disagree with available experimental data. A fusion evaporation experiment was conducted at the Laboratori Nazionali Legnaro (LNL – INFN) in 2015 using a 12C beam to bombard a stationary 24Mg target. The intent was to observe 34Ar in high spin states by observing the 2 neutron channel. Other stronger channels were opened in this reaction which produce a high background, making observing the 34Ar spectrum difficult. Gamma rays were detected by the GALILEO array composed of 25 High Purity Germanium (HPGe) detectors. The EUCLIDES charged particle detector associates charged particles being evaporated, whilst the neutron wall array tagged neutrons. Coincident events between the charged particles, neutrons, and gamma rays are used to create spectra of specific nuclei. The 2p reaction channel, associated with 34S, and pn reaction channel, associated with 34Cl, are analyzed and verified against known transitions in both nuclei. Contamination from other reaction channels complicated the analysis, as transitions from competing channels often overlapped. The 34Ar nucleus was not found in sufficient quantities to be detected, with the experimental reaction cross section calculated to be less than 91 μb.