A simulation study of the effect of drift electric fields on the response of radiation detectors using the PENELOPE code

The effect of the presence of a drift electric field on the response of gaseous and semiconductor radiation detectors to energetic X-rays (energies EphEph from 20 to 200 keV) is investigated using the PENELOPE code to simulate the photo-absorption and the slow-down of the electrons produced in Si, Ge, and Xe gas at 1 atm. For typical drift fields, the energy EdEd deposited in the detection media is calculated taking into account the energy exchanged by the electrons with the field. The analysis of the calculated EdEd distributions shows that the effect of the field on the distributions is negligible in Si and Ge semiconductor detectors, but not in Xe gas detectors, where for E/p=0.8Vcm-1Torr-1 the fluctuations introduced by the field for Eph≈180keV approach the intrinsic values for Xe, and the intrinsic discontinuity in linearity when EphEph crosses the Xe KK-edge (34.56 keV) is further reduced by ≈4%≈4%. The simulation data also suggest that this field effect may cause some deviations to the expected Gaussian response of Xe detectors to the absorption of monoenergetic photons.