Decay Properties and Hyperfine Interactions in Oriented Alpha-, Beta- and Gamma-emitting Nuclei
Doctoral thesis, 1993
The hyperfine interaction has often been described as the bridge between atomic physics and nuclear physics. On the one hand it enables us to study important nuclear phenomena which only manifest themselves in the strong internal fields originating from the surrounding electrons and on the other hand it enables us to study properties of the atomic system or of condensed matter using nuclear probes. In this work I will present three different experiments which all have in common that the hyperfine interaction is central for the technique.
The issue of lattice sites of francium in iron has been studied with two different techniques, integral Low Temperature Nuclear Orientation (LTNO) and emission channelling. Monte Carlo simulations of the system fitted to the channelling spectra reveal a large fraction of Francium in substitutional sites and hint at a possible complex site distribution. Using a two site model for the LTNO data, a large fraction in high field site, in agreement with the channelling data, is deduced. Furthermore, in parallel to the gamma- and alpha anisotropy measurement on 221Fr, alpha-anisotropy measurements have been performed on 225Ac, 217At and 209Po. Preliminary emission channelling data is also reported for 217At and 209Po.
The magnetic dipole moment of the 127,129Sb and 212,213Bi ground states have been measured and compared to results of shell model calculations. The technique of Nuclear Magnetic Resonance on Oriented Nuclei (NMR/ON) has been utilised to measure the magnetic dipole moments of the 127,129Sb ground states and the technique of integral LTNO to measure the moments of the 212,213Bi ground states. Comparison between the shell model particle-core coupling calculations and the measured values hints at a possible systematically very small collective g-factor in these regions. In parallel to the NMR/ON study an integral LTNO experiment was performed on the excited states in 127,129Te.
To reach further out from the valley of stability on the chart of nuclides, alternative methods to LTNO for polarisation have to be applied. One such method is the method of Tilted-Foil Polarisation (TFP). Two different studies have been performed aiming to develop the TFP technique for the measurement of ground-state properties of short- lived nuclei. The primary ion-beam from the ISOLDE facility, CERN, was post accelerated to 520 keV with a High Voltage platform to penetrate the tilted foils. Evidence for asymmetry induced by TFP was observed in the shape of a de-coupling curve between the holding field and the internal defect induced quadrupole interaction.