R. Turchetta

Spatial resolution of silicon microstrip detectors

Abstract The spatial resolution of silicon microstrip detectors is studied as a function of the main detector parameters and of the track angle. Several algorithms for finding the position of particle hits are presented and analysed. Analytic expressions of the spatial resolution are derived for the main algorithms. Using a Monte Carlo simulation, the spatial resolution is calculated for each algorithm and, for each detector design and track geometry, the algorithm that gives the best resolution is determined.

A submicron precision silicon telescope for beam test purposes

Abstract A precise and compact silicon microstrip detector telescope designed to provide reference information for charged particle tracks has been constructed. First operation results are presented. A signal over noise ratio higher than 100 has been obtained, resulting in a spatial resolution of 1.4 μm per detector, for a readout pitch of 50 μm. At a position in the center of the telescope, a track extrapolation error of 0.7 μm can be obtained for reconstructed tracks.

Novel mercuric iodide polycrystalline nuclear particles counters

Polycrystalline mercuric iodide nuclear radiation detectors have been produced in a novel technology. Unlike the normal single-crystal technology, there is no intrinsic limit to the surface on which these detectors can be produced. Detectors with areas up to about 1.5 cm/sup 2/, thicknesses from 30 to 600 /spl mu/m, and with single electrodes as well as microstrip and pixel contacts have been fabricated and successfully tested with photons in the range of 40-660 keV, /spl beta/ particles emitted from a Sr-Y source, and high energy (100 GeV) muons. Results on both charge collection and counting efficiency are reported as well as some very preliminary imaging results. The experimental results on charge collection have been compared with simulation, and a combined /spl mu//spl tau/ product 10/sup -7/ cm/sup 2//V for electrons has been estimated.

High-flux x-ray response of composite mercuric iodide detectors

A theological model is presented which analyses the sensitivity of composite detectors to a flux of x-rays emerging form a radiological x-ray generator. The model describes the many factor which influenced the x-ray response, for the case where the detector is composed of several layers of crystallites separated by a polymeric glue as is the case of composite HgI2 detectors fabricated by the screen print method. The model also describes the variation of the sensitivity with grain size and dielectric constant, taking into account the dielectric constant of the binder showing also the experimental result. Finally, the experimental result of the sensitivity vs. the voltage is shown for single crystal and composite HgI2 detectors and these results are compared with polycrystalline PbI2 and a-Se, which are the main material candidates for medical digital radiology.

Monolithic active pixel sensors for a linear collider

Abstract A novel technique for detecting minimum ionising particles (i.e. m.i.p.) was designed and a first prototype fabricated in a standard CMOS technology, guided by very high vertex detector performances required in future collider experiments. The device architecture resembles CMOS cameras, a recent alternative to CCD sensors for visible light imaging. The performance of the first prototype was evaluated with high energy π − beams at CERN. Preliminary test results demonstrate that the sensors detect m.i.p.s with very high efficiency and signal-to-noise ratio and provide excellent surface resolution.

Radiation-hard polycrystalline mercuric iodide semiconductor particle counters

Abstract Mercuric iodide polycrystalline radiation detectors, which can act as nuclear particle counters and for large area imaging devices, have been fabricated using three different methods. Response to X- and gamma rays, beta particles and to 100 GeV muons, as well as radiation hardness results are briefly described.

Evaluation of mercuric iodide ceramic semiconductor detectors

Mercuric iodide ceramic radiation detectors, which can act as nuclear particle counters, have been fabricated with single continuos electrical contacts and with linear strip contacts. They have been tested with different kinds of γ and β sources as well as in a high energy beam at CERN. The detectors were also successfully tested for radiation hardness with irradiation of 5*10 14 neutrons/cm 2 . The ratio of detected photons over the number of absorbed photons has been measured with T sources of different energies, and it ranges from 20% at 44 keV up to about 30% at 660 keV. An absolute efficiency of 70% has been measured for a 350 gm thick detector for β particles emitted by a 90 Sr source. Charge collection efficiency, defined as the amount of charge induced on the electrodes by a Minimum Ionizing Particle (MIP) traversing the detector, has been measured in two samples. The average collected charge fits well with a linear curve with slope of 35 electrons/(kV/cm) per 100 pro. This result is well described by a dynamic device simulation, where the free carrier mean lifetime is used as a free parameter, adjusted to a value of 1.5 ns, i.e. about 1/100 of the corresponding lifetime in single crystal HgI2 detectors. The response to MIP has also been studied with a high energy (100 GeV) muon beam in CERN. A preliminary beam profile is presented while a more detailed analysis is still in progress and will be presented elsewhere. These results together with the low cost of the material make ceramic HgI 2 detectors excellent candidates for large area particle tracking and imaging applications, even in a radiation harsh environment.

CHARACTERIZATION STUDIES OF PURIFIED HGI2 PRECURSORS

Abstract The ability of HgI 2 powders, used as precursors in mercuric iodide crystal growth, to produce high-quality detectors may be predicted by non-destructive methods like photoluminescence. In fact, it is possible to correlate the presence and the intensity ratio of specific bands in the photoluminescence spectrum of a HgI 2 crystal to its impurity content and stoichiometry. These quantities determine the detector grade that may be achieved using that starting material. Nine different HgI 2 precursors, obtained by different purification methods, have been characterized. The lowest impurity content is achieved via poly-ethylene treatment, which gives also a powder of relatively good stoichiometric quality.

Design of a low noise, self-triggered, monolithic preamplifier dedicated to silicon trackers and X-β imaging

Abstract A monolithic and triggerable charge amplifier has been implemented in a 1.2 μm CMOS technology. Initially developed for the LEP-DELPHI spectrometer (CERN), this architecture is also potentially useful for X and β imaging due to its noise performances (ENC = 110 e− rms + 10 e− rms/pf), low power consumption (Pd = 1.5 mW/channel), internal triggerability and shaping time adjustability between 1 and 2 μs.

VLSI readout for imaging with polycrystalline mercuric iodide detectors

Recently polycrystalline mercuric iodide have become available, for room temperature radiation detectors over large areas at low cost. Though the quality of this material is still under improvement, ceramic detectors have been already been successfully tested with dedicated low-noise, low-power mixed signal VLSI electronics which can be used for compact, imaging solutions. The detectors used are of different kinds: microstrips and pixels; of different sizes, up to about 1 square inch; and of different thickness, up to 600 microns. The properties of this first-generation detectors are quite uniform from one detector to another. Also for each single detector the response is quite uniform and no charge loss in the inter-electrode space have been detected. Because of the low cost and of the polycrystallinity, detectors can be potentially fabricated in any size and shape, using standard ceramic technology equipment, which is an attractive feature where low cost and large area applications are needed.