A. Esposito

Optimization of electric field distribution by free carrier injection in silicon detectors operated at low temperatures

We present a study of the modeling of the electric field distribution, which is controlled by injection and trapping of nonequilibrium carriers, in Si detectors irradiated by high neutron fluences. An analytical calculation of the electric field distribution in detectors irradiated by neutrons up to fluences of 1 /spl middot/ 10/sup 14/ to 5 /spl middot/ 10/sup 15/ cm/sup -2/ shows the possibility of reducing the full depletion voltage at low temperatures via hole injection. For this calculation, we use the detector operating parameters and equivalent neutron fluences expected for Large Hadron Collider experiments. The results of the calculation are in good qualitative agreement with published experimental data, lending strong support for the model and for an earlier proposal of electric field manipulation by free carrier injection.

First realization of a tracking detector for high energy physics experiments based on Josephson digital readout circuitry

We have designed and realized a prototype of a high energy particle microstrip detector with Josephson readout circuits. The key features of this device are: minimum ionizing particle sensitivity, due to the use of semiconductive sensors, fast speed and radiation hardness, due to the use of superconductive circuitry, and current discrimination, which allows the use of several types of semiconductors as detector (Si, GaAs, CVD-diamond) without loss in performances. The Josephson circuitry, made by a combination of RSFQ and latching logic gates, realizes an 8-bit current discriminator and parallel to serial converter and can be directly interfaced to room temperature electronics. This device, which is designed for application as vertex detector for the Compass and LHC-B accelerator experiments, has been tested with small radioactive sources acid will undergo to a test beam at the CERN SPS facility with 24 GeV/c protons. Current results and future perspectives will be reported.

Josephson tunnel junctions as fast nuclear particle position detectors

Abstract We present here some problems and solutions in using Josephson junctions as fast nuclear particle position detectors. The process of induced switching is modelled in terms of a reduction of the critical current due to a disturbed volume: the hotspot. The spurious thermal induced switching process is also taken into account. Calculations in order to choose the junction parameters are presented. The all refractory junctions fabrication technology developed is capable of satisfying design prescriptions.

Charge collection efficiency recovery in heavily irradiated silicon detectors operated at cryogenic temperatures

The charge collection efficiency (CCE) of high resistivity silicon detectors, previously neutron irradiated up to 2/spl times/10/sup 15/ n/cm/sup 2/, was measured at different cryogenic temperatures and different bias voltages. In order to study reverse annealing (RA) effects, a few samples were heated to 80/spl deg/C and kept at room temperature for several months after irradiation. For comparison other samples (NRA) where kept at -10 C after irradiation. The RA and NRA samples, measured at 250 V forward and reverse bias voltage, present a common temperature threshold at 150 K. Below 120 K the CCE is constant and ranges between 55% and 65% for the RA and NRA sample respectively. Similar CCE was measured for a device processed with low resistivity contacts (OHMIC), opening the prospect for a consistent reduction of the cost of large area particle tracking.

Development of radiation-hard particle detectors using Josephson tunnel junctions

Josephson tunnel junctions, due to their ultra-fast switching between different voltage states, are in principle capable of very fast position detection. This feature, together with the high radiation hardness of the constituting materials and the possibility of direct interfacing to ultra-fast superconductive logic families, makes Josephson tunnel junctions interesting candidates for new ultra-fast pixel detectors to be used at future colliders. Possible explanation of the detection mechanism in terms of an energy balance model is proposed, together with the identification of crucial parameters for detection sensitivity. A new approach for realising a detector integrated with read-out electronics is presented. Radiation hardness for both detector and electronics is discussed. High sensitivity to magnetic field is also addressed.