A GEANT4 Monte-Carlo simulation code for precision β spectroscopy

The measurement of the β asymmetry parameter in nuclear β decay is a potentially very sensitive tool to search for non V–A components in the charge-changing weak interaction. To reach the required precision (percent level) all effects that modify the emission pattern of the β radiation, i.e. the geometry of the setup, the effect of the magnetic field on the trajectories of β particles as well as (back)scattering in the source, on the sample holder and on the detector, have to be correctly taken into account in the analysis of the data. A thorough study of these effects and a new method based on detailed GEANT4 Monte-Carlo simulations that was developed for this purpose is presented here. The code was developed for β asymmetry measurements by means of the Low Temperature Nuclear Orientation (LTNO) method, but can in principle be generalized to other experimental setups using other polarization techniques.