Position reconstruction in a scintillator coupled to proximity focused HPDs using the light division method

The light generated by an ionizing particle crossing a scintillator is collected by means of light guides coupled to two proximity focused Hybrid Photo Diodes (HPDs) and used to measure the position along the slab. Two scintillators with dimensions (20×3.1×0.23) cm3 and (60×5×0.5) cm3 have been tested with a collimated 90Sr source. The relation between reconstructed position and nominal position of the source is linear through all the scintillator length. The accuracy in the position depends on the attenuation length, the number of photoelectrons and the signal-to-noise ratio of the HPD. The resolutions obtained with a MIP for the two slabs are σz=3.8 cm and σz=15.9 cm, respectively. This method will be used in the inner scintillator array of the FINUDA experiment.