Development of a dedicated laser-polarization beamline for ISOLDE-CERN

This thesis presents measurements of the b-asymmetry of spin-polarized 35Ar in different crystals and at different temperatures. These measurements form the first phase of a research project that aims to measure the b-asymmetry parameter with a relative precision of 0.5%. This thesis details technical developments of the beamline that was used to perform these measurements. These developments include the specifications of the different magnetic fields and the design and construction of the different coils. Furthermore, an existing rate equation formalism was extended to permit calculations in which an arbitrary number of levels and lasers interact. This extension proved crucial in optimizing the optical pumping scheme of 35Ar and achieving maximal polarization. In addition, analysis techniques based on likelihood maximization and Monte-Carlo probing of the resulting parameter distribution are described here. After implantation of the spin-polarized 35Ar into NaCl and KCl crystals, an asymmetry of about 1% was observed at low temperatures (10K). This result is compared to theoretical estimates, taking into account several processes which were investigated numerically: the optical pumping process, the rotation of the nuclear spin in the applied magnetic fields and the path of the emitted b-particles. This comparison shows agreement between the data and the simulations, although the b-scattering simulations do come with a large systematic uncertainty due to problems with the simulation software. Furthermore, a growth of an impurity layer on top of the crystal surface limited the measurement time: after every hour of measurement, a two hour cycle of heating and cooling down the crystal was required to restore the observed signal. Future technical challenges will include improving the vacuum system to extend the useful measurement time at cryogenic temperatures and reduce the duty cycle loss. Preliminary studies of techniques to enhance the polarization indicate that laser re-ionization would be most interesting for the future of the project.