Two different GaAs crystals, one LEC and one LPE, have been irradiated with photons of various energies, to compare their response in view of a possible application for digital radiography. Experimental results include I–V curves, charge collection efficiency, detection efficiency and energy resolution as a function of bias. A comparison is made with a simulation program that takes into account X-ray interactions, electric field and charge trapping inside the material.

Detectors with a p-i-n structure based on Liquid Encapsulated Czochralski (LEC) grown Semi-Insulating (SI) GaAs have been fabricated. The current-voltage (I–V) characteristics and their response to γ-rays have been studied. Measurements of the peak charge collection efficiency (cce) have been compared with a model assuming a uniform electric field. The comparison indicates that this field is not uniform. The peak cce at 500 V is found to be 52% and 82% in 400 μm and 200 μm thick detectors respectively. The resolution of the 57Co full energy peak is between 10% and 13% at 400 V.

Preliminary results are presented on the performance of double-sided microstrip detectors using Schottky contacts on both sides of a semi-insulating (SI) GaAs substrate wafer, after exposure to 10(14) neutrons cm-2 at the ISIS facility. A qualitative explanation of the device behaviour is given.

Progress in the development of detectors based on semi‐insulating GaAs for experiments at future hadron colliders is presented. Effects of neutron and gamma irradiation at the levels of 1014 ncm−2 and 20 MRad respectively, have been shown to be small. Testbeam studies have shown that microstrip detectors can detect minimum ionizing particles with a good signal to noise ratio despite having low charge collection efficiencies. The problem of charge loss in the detectors is now better understood and new detectors have shown improved charge collection efficiencies.

The GaAs detectors for minimum ionizing particles fabricated with commercial undoped SI GaAs show good quality as minimum ionizing particle detectors. A discussion is given of the present understanding of the charge transport mechanism in the detectors since it influences their charge collection efficiency.

Progress with Schottky diode and p i n diode GaAs detectors for minimum ionizing particles is reported here. The radiation hardness and potential speed of simple diodes is shown to be more than competitive with silicon detectors. A discussion is given of the present understanding of the charge transport mechanism in the detectors as it influences their charge collection efficiency. Early results from micro-strip detectors are also described, (which are relevant for high radiation regions of LHC detectors near the beam pipe and in the forward region).

Progress on the development of GaAs solid state detectors is presented. 80% charge collection efficiency has been achieved, and double sided detectors with metal rectifying contacts have been tested. Measurements of capacitance and tests with SEM are giving more information on the behaviour of these devices.

Purpose of this note is to propose a search for typical signatures produced by charginos, neutralinos and sleptons on the basis of two supergravity model predictions, at the highest e+ e− energy which will be available with LEP-II. The typical signatures are of two main classes: i) «pure leptonic» states; ii) «mixed lepton-jets» states. The «pure leptonic» states consist of acoplanardi-leptons with «leading» and «non-leading» leptonic components plusmulti-di-lepton states. All with at least two missing momenta. The «mixed lepton-jets» states contain at least two jets and one or three leptons plus missing momenta. All these final states represent clear signatures for SUSY. Cross-sections and branching ratios are computed using two «local» supersymmetry models:i.e. the minimalSU(5) supergravity and theSU(5)×U(1) supergravity. The corresponding numbers of «pure leptonic» and of «mixed lepton-jets» final states are computed. We also discuss the upgrading needed in an experimental set-up at LEP-II especially suited for the detection of the supersymmetry signals expected on the basis of the two supergravity models quoted. These models are at present the most reliable in terms of physically sound assumptions.

Microstrip detectors have been constructed from gallium arsenide (GaAs) wafers made from undoped LEC (liquid-encapsulated Czochralski) semi-insulating substrate material. Tests were performed using minimum ionising particles to ascertain their properties as charged particle detectors. The results show that the devices work wellm, with good signal-to-noise ratio (typically 7). The effects of gamma ray and neutron irradiation have been studied and shown to be small up to levels exceeding 20 Mrad and 1014 n/cm2, respectively.

The first phase of a study of GaAs as a base material for solid-state detectors has been completed. The main motivation behind this study is the greater radiation resistance of integrated circuits made of GaAs (compared with Si). Many diodes, of different sizes and shapes but built with the same technique, have been tested electrically and as detectors, using α sources and minimum-ionizing particles. The tests show that these devices work with a full detection effeciency, although there is evidence for trapping of a fraction of the charge produced by the particle inside the semiconductor.