E. Borchi

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.

Deep-level transient spectroscopy measurements of majority carrier traps in neutron irradiated n-type silicon detectors

Abstract The effect of damage produced in silicon detectors by neutron irradiation at room temperature is examined by using the experimental technique of deep-level transient spectroscopy. The production of three defects, the A centre, the E centre, and the divacancy, is reported. The divacancy is especially important in neutron damage in silicon. There is evidence of some defects generated during annealing. It has been found that the properties of the point defects outside the clusters are the main results obtained with DLTS methods.

Pulse height distribution and radiation tolerance of CVD diamond detectors

The paper reviews measurements of the radiation tolerance of CVD diamond for irradiation with 24 GeV/c protons, 300 MeV/c pions and 1 MeV neutrons. For proton and neutron irradiation, the measured charge signal spectrum is compared with the spectrum calculated by a model. Irradiation by particles causes radiation damage leading to a decrease of the charge signal. However, both the measurements and the outcome from the model shows that for tracker applications this drawback is at least partly counterbalanced by a narrowing of the distribution curve of the charge signal. In addition, we observed after proton irradiation at the charge signal spectrum a decrease of the number of small signals. As a result, the efficiency of a CVD diamond tracker is less affected by irradiation than the mean charge signal. (11 refs).

Thermoluminescence analysis of - and -irradiated chemical vapour deposited diamond films

The thermoluminescent (TL) response of a set of synthetic diamond films obtained by chemical vapour deposition was investigated using gamma and beta radioactive sources over the dose range from 60 mGy to 3.5 Gy. A TL response linear with dose was generally observed. A numerical curve-fitting procedure was applied to deconvolute the complex-structured TL glow curves, which were found to be composed at most by five peaks in the temperature range between C to C. A short preheat treatment after irradiation allowed us to obtain a very stable smooth-shaped glow curve composed of a unique peak close to C. This isolated structure followed first-order kinetics over the whole dose range. The activation energy of the main peak, eV, was determined considering all samples and all irradiation doses using both the peak shape method and the fitting procedure. The corresponding frequency factor was estimated to be within the range -. The TL sensitivity of the diamond films calculated considering the isolated high-temperature peak compares favourably with that measured with a set of LiF TLD100 and TLD700 standard dosimeters.

Electron-ion pseudopotentials in the noble metals

Abstract Pseudopotential form-factors for Cu, Ag and Au are evaluated by means of a simple model potential.

A method of TSC analysis of shallow levels applied to silicon

A distortion of the thermally stimulated currents (TSC) line-shape and peak position has been observed in the temperature range 8 - 20 K in n-type silicon. This behaviour has been explained through the Poole - Frenkel effect, considering both the change of the depletion depth due to the thermal release of carriers and the corresponding variation of the emission constant due to the change in the electric field. A numerical fit has been developed, the results of which are in good agreement with the experimental data. The method is quite general and can be applied to the shallow-level analysis of less popular semiconductor materials.

A comparative study of the thermoluminescent response to beta irradiation of CVD diamond and LiF dosimeters

Abstract The thermoluminescent (TL) response of Chemical Vapour Deposited (CVD) diamond films to beta irradiation has been investigated. A numerical curve-fitting procedure, calibrated by means of a set of LiF TLD100 experimental spectra, has been developed to deconvolute the complex structured TL glow curves. The values of the activation energy and of the frequency factor related to each of the TL peaks involved have been determined. The TL response of the CVD diamond films to beta irradiation has been compared with the TL response of a set of LiF TLD100 and TLD700 dosimeters. The results have been discussed and compared in view of an assessment of the efficiency of CVD diamond films in future applications as in vivo dosimeters.

Studies of deep levels in high resistivity silicon detectors irradiated by high fluence fast neutrons using a thermally stimulated current spectrometer

Measurements of deep level spectra for high resistivity silicon detectors irradiated by high fluence fast neutrons (up to 10/sup 14/ n/cm/sup 2/) have been performed using a thermally stimulated current (TSC) spectrometer. Nine new defect levels with peaking temperatures of respectively 26 K, 34 K, 41 K, 47 K, 90 K, 110 K, 135 K, 147 K and 155 K begin to appear for fluences over 10/sup 13/ n/cm/sup 2/. All peaks are strongly dependent on the filling forward voltage V/sub fill/, or injection current, especially for high fluences. Energy levels inside the band gap and trap concentrations corresponding to each of the TSC peaks totaling at most 18, have been studied systematically and possible relations to lattice defects have been discussed. >

The local hardening effect on electromagnetic showers. A way for signal equalization in Si/high-Z hadron calorimeters

Abstract The condition for obtaining the linear response of a calorimeter to hadronic showers and an energy resolution improving as the incident energy increases is the equalization between the electromagnetic and the hadronic signals. This equalization is obtained within a new approach exploiting a local hardening effect that is realized by inserting low-Z absorbers next to the silicon readout detectors. In this way, the calorimeter response to the electromagnetic component of the hadronic shower is reduced. A systematic investigation of the visible energy response for electromagnetic showers in Si/U and Si/W calorimeters has been carried out for incoming electron energies of 2, 4, and 6 GeV. The insertion of low-Z material (G10 plates) in front or at the rear of the silicon detectors allows a fine tuning of the calorimeter response.

Silicon sampling hadronic calorimetry: A tool for experiments at the next generation of colliders

Abstract The SICAPO Collaboration project to build a perfectly compensating hadron calorimeter using silicon as the active medium, is described. The insertion of low-Z material (G10 plates) in front or at the rear of the silicon detectors allows fine tuning of the calorimeter response to electromagnetic showers. This is a new approach to obtaining compensation. The tuning can be exploited to obtain e/π = 1 (compensation condition). The expected performance ranks this calorimeter among the best candidates to face the severe constraints requested by the next generation of colliders.