Analysis of the radiation tolerance of the LHCb silicon vertex detector

This note analyses the radiation tolerance of the LHC-B silicon vertex detector in the framework of the latest damage models put forward by the ROSE / CERN RD 48 Collaboration. The calculations assume constant temperature and constant flux for a one year beam period of 240 d. It is found that the ultimate failure of the detectors is due to the damage-induced doping changes causing the loss of sensitive volume. Increases in the leakage current and carrier trapping stay at a tolerable level. Given a suitable operating temperature (5 degree C) and initial resistivity, detectors of 150 _m (480 \Omega cm) and 200 _m (850\Omega cm) thickness are expected to remain fully depleted with 200 V up to equivalent 1-MeV neutron fluences of 5 \Theta 1014cm\Gamma 2and 9 \Theta 1014cm\Gamma 2, respectively. Admitting partially depleted operation, the lower benchmarkfigure of 7000 collected electrons is reached at radiation doses as high as 8 \Theta 1014cm\Gamma 2 and1 \Theta 1015cm\Gamma 2, respectively. A conservative 50 4.065235e-309rror in the quoted values is due to the uncertainty in the experimentally determined constants of the damage models.1