Cryogenic temperature performance of heavily irradiated silicon detectors

The charge collection e$ciency (CCE) of silicon detectors, previously irradiated with high neutron #uences, has been measured at 4.2, 77 and 195 K. The CCE recovery measured after 1.2]1014 n/cm2 is 100% at a bias voltage of 50 V. For 2]1015 n/cm2 the most probable signal collected for minimum ionising particles is 13 000 electrons, corresponding to 50% CCE, at a bias voltage of 250 V. Negligible di!erence has been observed between 77 and 4.2 K operation, while no recovery was measurable at 195 K. The timing of the signal was measured to be better than 5 ns. The samples were irradiated and stored at room temperature and cooled only when operated. Reproducible results were obtained after several weeks and several thermal cycles. ( 1999 Elsevier Science B.V. All rights reserved.