RUI: Nuclear Magnetic Moment Measurements Using On-Line B-NMR Spectroscopy

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Nuclear ground state magnetic moments of short-lived B-unstable nuclei are measured using B radiation-detected nuclear magnetic resonance (B-NMR) spectroscopy in conjunction with recoil mass separation and tilted foil polarization. After separation from the beam and other reaction products, recoil nuclei are polarized by passage through an array of tilted carbon foils, after which they are implanted in a crystal host immersed in a strong magnetic field whose direction coincides with the polarization axis. Angular distribution of the B-decay is asymmetric parallel and anti-parallel to the polarization axis owing to the parity- violating nature of B-decay. Search for the NMR involves applying a weak RF magnetic field oriented perpendicular to the polarization axis, and finding the frequency at which decay asymmetry disappears. Knowledge of this frequency and of the magnetic field in which the nucleus precesses allows simple extraction of the nuclear magnetic moment. The current focus of this project is 23Mg, the last T = 1/2 mirror nucleus in the sd- shell whose magnetic moment is unknown. Successful measurement of its moment will supply an important nuclear datum to the study of mirror nuclei in the sd-shell, and will contribute to the understanding of the shell model structure of the nucleus. Similar measurements are planned for other nuclei, both in the sd- and fp-shells.