V.G. Palmieri

Review of the development of diamond radiation sensors

Abstract Diamond radiation sensors produced by chemical vapour deposition are studied for the application as tracking detectors in high luminosity experiments. Sensors with a charge collection distance up to 250 μm have been manufactured. Their radiation hardness has been studied with pions, proton and neutrons up to fluences of 1.9×10 15 π cm −2 , 5×10 15 p cm −2 and 1.35×10 15 n cm −2 , respectively. Diamond micro-strip detectors with 50 μm pitch have been exposed in a high-energy test beam in order to investigate their charge collection properties. The measured spatial resolution using a centre-of-gravity position finding algorithm corresponds to the digital resolution for this strip pitch. First results from a strip tracker with a 2×4 cm 2 surface area are reported as well as the performance of a diamond tracker read out by radiation-hard electronics with 25 ns shaping time. Diamond pixel sensors have been prepared to match the geometries of the recently available read-out chip prototypes for ATLAS and CMS. Beam test results are shown from a diamond detector bump-bonded to an ATLAS prototype read-out. They demonstrate a 98% bump-bonding efficiency and a digital resolution in both dimensions.

Tracking with CVD diamond radiation sensors at high luminosity colliders

Recent progress on developing diamond-based sensors for vertex detection at high luminosity hadron colliders is described. Measurements of the performance of diamond sensors after irradiation to fluences of up to 5/spl times/10/sup 15/ hadrons/cm/sup 2/ are shown. These indicate that diamond sensors will operate at distances as close as 5 cm from the interaction point at the Large Hadron Collider (LHC) for many years at full luminosity without significant degradation in performance. Measurements of the quality of the signals from diamond sensors as well as spatial uniformity are presented. Test beam results on measurements of diamond-based microstrip and pixels devices are described.

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.

Effect of intense proton irradiation on properties of Josephson devices

We have experimentally investigated the effects of intense proton beam irradiation (up to 10/sup 15/ p/cm/sup 2/) on Josephson junctions and junction arrays. The devices we have studied were realized using state of the art full-Nb technology, employing same materials and thicknesses of common Josephson digital circuit designs. We have analysed in detail the magnetic field dependence of the junction critical current, and the quasiparticle tunneling current, in order to observe possible occurrence of permanent changes produced by the ionizing particles. No evidence of radiation induced damage on the properties of the junctions has been found.

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.

Hybrid Superconducting Pixel Detector

A new position sensitive cryogenic detector for high energy particles based on Josephson Tunnel Junctions (JTJs) is proposed. This consists of a semiconductive substrate to transduce the energy of particles in charge and of a JTJ as a current driven sample and hold circuit. The possibility of coupling to high-speed Josephson logic families and the sensitivity to magnetic fields are also addressed.

Improvement of the phase transition homogeneity of superheated superconducting tin granules

Abstract A considerably improved phase transition homogeneity was observed with superheated superconducting Sn spheres as a result of laser melting and fast cooling. These spheres exhibited a very homogeneous phase transition behaviour independent of the orientation of the spheres with respect to the direction of the external magnetic field. Compared to previously untreated Sn spheres the spread of the phase transition boundaries was reduced by almost an order of magnitude. In addition, we studied mass production of Sn structures using vacuum evaporation and deposition. First encouraging results are reported.

Temperature dependence of the charge collection efficiency in heavily irradiated silicon detectors

Abstract Two silicon diode detectors, Al/n + /n/p + /Al, were exposed to fluences of 1.19×10 14 and 2.23×10 15 equivalent 1 MeV neutrons/cm 2 , respectively. After this exposure the detectors were stored at room temperatures for 2 yr (1.19×10 14 ) and six months (2.23×10 15 ). During this time they were thermally cycled around 4.2 K and room temperature a number of times in order to make measurements. The charge collection efficiency is measured to be (at 77 K) 100% for the less severely irradiated detector and 50% for the detector exposed to high levels of radiation. The same results apply to operation at 4.2 K, while no recovery is observed at 195 K. By examining the signal response of the irradiated detectors to α particles, it is shown that some of the radiation damage after reverse annealing is in the form of electron and hole traps, which are either weakly, or not at all, temperature dependent.

Status report on the ORPHEUS dark matter detector and on its SQUID readout system

Abstract We report the status of the ORPHEUS dark matter experiment. The detector will consist of about 1 kg of superheated superconducting Tin granules and will be operated below 0.5 K. measurements with a 32 cm 3 target, read by a single SQUID channel, are presented. Experience has been gained with cryogenic tests, performed with a test detector chamber, mounted via a side access to the cryostat.

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.