In-beam spectroscopy of high-K states in No-254

• Main Author: Ward, A. J.
• Published: University of Liverpool 2016
• Subjects: 539.7
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.721952

The transfermium nucleus No-254 (Z = 102, N = 152) has been studied in a recoil-decay tagging experiment using the SAGE in-beam spectrometer, RITU gas-filled separator and GREAT focal-plane spectrometer at the Accelerator Laboratory of the University of Jyväskylä (JYFL). Both γ rays and conversion electrons from the ground-state band of No-254 have been observed with SAGE. Coincidences between them can be seen and it is possible to measure internal conversion coefficients for some transitions in the band. This shows that they have E2 multipolarity, as expected for a rotational band built on a Kπ = 0+ state. The two previously identified K isomers in No-254 have also been seen. In the prompt data tagged on the slow isomer’s decay the prominent 605 keV transition from previous decay spectroscopy experiments is not seen with the expected intensity. This allows one of the previously proposed level schemes to be ruled out. It is possible that this transition is not seen in the in-beam data at all and the peak at this energy is entirely from inelastic neutron scattering reactions within the SAGE germanium detectors. If this is the case the 605 keV transition could directly depopulate the fast isomer into a band built on the slow isomer without any intermediate structure. There is not enough data to measure γ-ray branching ratios in the band built on the slow isomer so a new method has been developed to determine the single-particle structure of the isomer by comparing the in-beam conversion-electron spectrum above it with Geant4 simulations of the same level scheme with a varying single-particle g factor. This suggests that the structure of the slow isomer is the 7/2+[624]ν ⊗ 9/2-[734]ν two-neutron state.