Abstract
Silicon and diamond detectors operated in a superfluid helium bath are currently being considered for the upgrade of the LHC beam loss monitoring system. The detectors would be installed in immediate proximity of the superconducting coils of the triplet magnets. We present here the results of the in situ irradiation test for silicon detectors using 23GeV protons while keeping the detectors at a temperature of 1.9K. Red laser (630nm) Transient Current Technique and DC current measurements were used to study the pulse response and collected charge for silicon detectors irradiated to a maximum radiation fluence of 1×1016p/cm2. The dependence between collected charge and irradiation fluence was parameterized using the Hecht equation and assumption of a uniform electric field distribution. The collected charge was found to degrade with particle fluence for both bias polarities. We observed that the main factor responsible for this degradation was related to trapping of holes on the donor-type radiation-induced defects. In contrast to expectations, along with formation of donors, acceptor-type defects (electron traps) are introduced into the silicon bulk. This suggests that the current models describing charge collection in irradiated silicon detectors require an extension for taking into account trapping at low temperatures with a contribution of shallow levels. New in situ irradiation tests are needed and planned now to extend statistics of the results and gain a deeper insight into the physics of low temperature detector operation in harsh radiation environment.
Highlights
Silicon and diamond detectors operated in a superfluid helium bath are currently being considered for the upgrade of the LHC beam loss monitoring system
Current pulse response of silicon detectors irradiated at 1.9 K The pulse signals described were measured in the the maximum amplitude and the following decay indicate that the electric field maximum Emax is near the nþ contact, i.e. space charge sign inversion (SCSI) occurred in the fluence interval between the previous and this measurement
Though the difference in the fluence does not exceed 10%, the was irradiated under reverse bias of 100 V, and the Transient Current Technique (TCT) measurements were performed the bias, which may well be due to the reduction of the trapping time during a period of several minutes preceding the arrival of the following spill
Summary
This hinders from the introduction of vacancy-related acceptortype defects (VV, V2O, etc.), which control the accumulation of negative charge in the detector bulk and are responsible for the degradation of silicon detector characteristics, including charge collection This gives us hope that the radiation hardness of silicon detectors will be adequate in superfluid helium media. Verbitskaya et al / Nuclear Instruments and Methods in Physics Research A 796 (2015) 118–125 The work on this project started at CERN in 2011 included tests of nonirradiated silicon and diamond detectors operating at $ 2 K and in situ irradiation test of these detectors at 1.9 K [7,8,9]. We analyze the experimental results looking for specific features of radiation-induced defect formation at such low temperature
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