Tilted-foil polarisation and magnetic moments of mirror nuclei at ISOLDE

We report here on the first measurement in an experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic moments of short-lived radionuclides. The 60~keV ISOLDE beam from the GPS separator is boosted in energy by a 200~kV high-voltage platform, on which the whole experiment is mounted, in order to achieve sufficiently high energy for transmission through the foils of a tilted-foil setup. The 520~keV $^{23}$Mg(2$^+$) nuclei are polarized by the tilted foil technique and the resulting 0$^o$ - 180$^o$ $\beta$- asymmetry is monitored as a function of the frequency of an rf-applied perturbing magnetic field in an NMR setup.\\ In this experiment, earlier asymmetry measurements were confirmed and an NMR resonance was observed, corresponding to a preliminary value of the magnetic moment of 0.533(6) n.m., in agreement with a previous measurement. The measured asymmetry as function of NMR frequency and the fitted resonance curve are presented in the figure. During the experiment, problems were encountered with the buildup of contamination on the stopper surface. Improvements to the experimental setup are presently being designed, aiming at improved vacuum and possibly lower temperature. This will help pave the way for measurements of magnetic moment of T=3/2 nuclei in the s-d shell and T=1/2 f-shell nuclei. The study of relaxation times and other solid-state phenomena in semi-conductors and other materials of interest will also be possible with this technique.\\ \\\\ \\