Silicon strip detectors and photodiodes were irradiated in an 800 MeV proton beam. The change of the effective doping concentration was monitored by measuring diode C-V curves. Type inversion is observed at a fluence Φ = 1.5 × 1013 cm−2. Further evidence for type inversion is obtained from a study of pulses generated by an infrared LED in silicon strip detectors. A two-level parametrization is used to describe donor removal and acceptor state creation during proton irradiation: Neff = N0 exp(−cφ)−βφ. We measure values of c = (5.5 ± 1.1) × 1014 cm2 and β = (0.031 ± 0.006) cm−1. After type inversion the depletion voltage increases with proton fluence. This may set the limit for the lifetime of silicon detectors at future colliders. However, the occurence of type inversion does not degrade the performance of silicon strip detectors. The effective doping concentration showed a complex post irradiation behaviour. After a short term annealing period the doping concentration increased beyond the value that had been reached immediately after the exposure.

Type inversion in silicon detectors

In the framework of the CERN-RD50 Collaboration, the adoption of p-type substrates has been proposed as a suitable mean to improve the radiation hardness of silicon detectors up to fluencies of 1times10 16 n/cm2. In this work two numerical simulation models will be presented for p-type and n-type silicon detectors, respectively. A comprehensive analysis of the variation of the effective doping concentration (Neff), the leakage current density and the charge collection efficiency as a function of the fluence has been performed using the Synopsys T-CAD device simulator. The simulated electrical characteristics of irradiated detectors have been compared with experimental measurements extracted from the literature, showing a very good agreement. The predicted behaviour of p-type silicon detectors after irradiation up to 1016 n/cm2 shows better results in terms of charge collection efficiency and full depletion voltage, with respect to n-type material, while comparable behaviour has been observed in terms of leakage current density

Numerical Simulation of Radiation Damage Effects in p-Type and n-Type FZ Silicon Detectors

We report on the measurement of the neutron radiation hardness of silicon photomultipliers (SiPMs) manufactured by Hamamatsu Corporation in Japan and SensL in Ireland. Samples from both companies were irradiated by neutrons created by a 1 GeV electron beam hitting a thin lead target at Jefferson Lab Hall A. More tests regarding the temperature dependence of the neutron radiation damage and self-annealing were performed on Hamamatsu SiPMs using a calibrated Am–Be neutron source from the Jefferson Lab Radiation Control group. As the result of irradiation both dark current and dark rate increase linearly as a function of the 1 MeV equivalent neutron fluence and a temperature dependent self-annealing effect is observed.

Radiation Hardness Tests of SiPMs for the JLab Hall D Barrel Calorimeter

We present a study of how temperature affects the change in the depletion voltage of silicon PIN detectors damaged by radiation. We study the initial radiation damage and the short-term and long-term annealing of that damage as a function of temperature in the range from −10°C to +50°C, and as a function of 800 MeV proton fluence up to 1.5×1014 p/cm2. We express the pronounced temperature dependences in a simple model in terms of two annealing time constants which depend exponentially on the temperature.

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Temperature dependence of the radiation induced change of depletion voltage in silicon PIN detectors

Purpose: Intensity modulated radiation therapy (IMRT) utilizes the technology of multileaf collimators to deliver highly modulated and complex radiation treatment. Dosimetric verification of the IMRT treatment requires the verification of the delivered dose distribution. Two dimensional ion chamber or diode arrays are gaining popularity as a dosimeter of choice due to their real time feedback compared to film dosimetry. This paper describes the characterization of a novel 2D diode array, which has been named the “magic plate” (MP). It was designed to function as a 2D transmission detector as well as a planar detector for dose distribution measurements in a solid water phantom for the dosimetric verification of IMRT treatment delivery. Methods: The prototype MP is an 11 � 11 detector array based on thin (50 lm) epitaxial diode technology mounted on a 0.6 mm thick Kapton substrate using a proprietary “drop-in” technology developed by the Centre for Medical Radiation Physics, University of Wollongong. A full characterization of the detector was performed, including radiation damage study, dose per pulse effect, percent depth dose comparison with CC13 ion chamber and build up characteristics with a parallel plane ion chamber measurements, dose linearity, energy response and angular response. Results: Postirradiated magic plate diodes showed a reproducibility of 2.1%. The MP dose per pulse response decreased at higher dose rates while at lower dose rates the MP appears to be dose rate independent. The depth dose measurement of the MP agrees with ion chamber depth dose measurements to within 0.7% while dose linearity was excellent. MP showed angular response dependency due to the anisotropy of the silicon diode with the maximum variation in angular response of 10.8% at gantry angle 180 � . Angular dependence was within 3.5% for the gantry angles 675 � . The field size dependence of the MP at isocenter agrees with ion chamber measurement to within 1.1%. In the beam perturbation study, the surface dose increased by 12.1% for a 30 � 30 cm 2 field size at the source to detector distance (SDD) of 80 cm whilst the transmission for the MP was 99%. Conclusions: The radiation response of the magic plate was successfully characterized. The array of epitaxial silicon based detectors with “drop-in” packaging showed properties suitable to be used as a simplified multipurpose and nonperturbing 2D radiation detector for radiation therapy dosimetric verification. V C 2012 American Association of Physicists in Medicine.

Characterization of a novel two dimensional diode array the "magic plate" as a radiation detector for radiation therapy treatment.

Silicon strip detectors with 5 μm spatial resolution have been used during 1982–1985 in the ACCMOR spectrometer at CERN. After a local beam flux of about 1014 minimum ionizing particles per cm2 we observe a significant increase in dark current and systematic distortions in the measured coordinates which are explained in terms of a decrease in the effective donor concentration.

A. Löffler

Papers

Radiation damage in silicon strip detectors