A GEANT4 Monte-Carlo simulation code for precision ββ spectroscopy

The measurement of the ββ asymmetry parameter in nuclear ββ decay is a potentially very sensitive tool to search for non VV–AA components in the charge-changing weak interaction. To reach the required precision (percent level) all effects that modify the emission pattern of the ββ radiation, i.e. the geometry of the setup, the effect of the magnetic field on the trajectories of ββ 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 ββ 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.