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We measured the charge collection efficiency and energy resolution at 60 keV and 122 keV for single-element Cd/sub 0.8/Zn/sub 0.2/Te semiconductor detectors 2/spl times/10/spl times/10 mm/sup 3/, irradiated transverse to the electric field, in view of their possible use for digital radiography. Charge collection efficiency, energy resolution and charge collection time have been measured as a function of the bias voltage. The detector's imaging performance was evaluated, using a scanning procedure, by measurements (at 60 keV) of the line spread function and edge response function of the imaging system; metallic test objects and bone tissue were imaged. Image contrast values as low as C=10% were obtained for a minimum 5:1 S.N.R.

We report here experimental results of the response of two Cd 0.8 Zn 0.2 Te detectors when irradiated with 511 keV photons transverse to the electric field, in view of their possible use for positron emission tomography. Measurements include charge collection time, coincidence resolution time, electron mobility and lifetime, charge collection efficiency, energy resolution and detection efficiency.

A digital autoradiography system based on double sided silicon strip detectors (1.6 × 1.6 mm2 active surface with 100 μm pitch) has been developed and successfully tested with beta-emitting tracers. It is shown here that the system is able to perform imaging of organic material with specific sensitivity as small as 0.002 nCi/mm2, and to record activity measurements with good linearity in the range 0.002–20 nCi/mm2. Autoradiographic images of clusters of mammary cells marked with ortho-(32P)phosphate, obtained with an exposure time of about 10 min are presented.

The use of a double sided mu -strip silicon crystal for X-ray detection is being investigated. The detector is 300 mu m thick and the read-out pitch is 100 mu m for both sides. It operates in capacitance charge division mode by means of floating strips between read-out strips. The detector has been irradiated by /sup 241/Am and /sup 109/Cd sources. Different zones within the 100- mu m read-out pitch have been individually exposed. The following characteristics have been studied as a function of the impact point of the photon: (a) the charge collection mechanism; (b) the relative detection efficiency; (c) the energy resolution; and (d) the spatial resolution. The absolute efficiency of the detector has been measured at three energy values. >

We present some additional results obtained with the BETAview system, a digital system for real time /spl beta/-imaging based on semiconductor pixel detectors and on a single photon counting read-out chip. We describe the system assembled with a Si detector, 300-/spl mu/m thick, segmented into 64 /spl times/64 square pixels with 170-/spl mu/m pitch. The solid-state pixel array detector is bump-bonded pixel by pixel to a low threshold, single particle counting electronics, the photon counting chip (PCC) developed by the Medipix1 Collaboration for biomedical applications. Each cell (corresponding to a detector pixel) of the front-end chip has a maximum count rate of 2 MHz, a minimum nominal threshold of 1400 e/sup -/ (corresponding about 5 keV in Si), and contains a 15-bit counter. The detector sensitive area is about 1 cm/sup 2/, but several detectors could be assembled in arrays. The measured background counts were about 3.5/spl times/10/sup -2/ cps/cm/sup 2/, which implies a very high sensitivity of the device. The detection threshold used in this experiment was /spl sim/15 keV. We show the results obtained in the real-time monitoring of two biological dynamic processes: an amino acid uptake by living cells and the thermal denaturation process of oligonucleotides. Specifically, we have followed over time the accumulation of a marked amino acid ([/sup 14/C]L-Leucine) into Octopus vulgaris eggs cells. The results, described in Section III-B, show that after about 20 min from the beginning of the uptake process, the radioactively marked eggs become clearly visible over the background culture radioactive medium. In Sections III-C and III-D, we also describe the successful performance of the /spl beta/-imaging system in genetic studies involving the real time reconstruction of denaturation and kinetics curves for two different /sup 32/P-radiolabeled nucleotides.

A portable system has been developed for the control and the readout of a 64/spl times/64 pixel silicon hybrid detector (1.1/spl times/1.1 cm/sup 2/ active area), bump-bonded to the Medipix1 readout chip. This system was originally designed for biomedial imaging applications and is based on standard commercial digital I/O boards and a compact dedicated interface (p-MUROS), connected to the portable PC. The Medipix1 chip is hosted in a 257 Pin Grid Array chip carrier directly placed on the p-MUROS board. This board is the simplified version of the MUROS1 readout board already developed in the framework of the Medipix collaboration. User-friendly software system (Medisoft 3.3) has been written to provide control of the system and image acquisition, display and processing. This complete hardware/software imaging system has been used with laboratory /spl alpha/, /spl beta/ and /spl gamma/ sources for test purposes and represents the portable version of a desktop imaging system developed for /spl beta/-autoradiography. The system description and complete imaging tests are presented. Additional applications include the monitoring of the flux and the energy spectrum of X-rays tubes.

We have investigated the detection performance of GaAs detectors made with different thickness and contact geometries. A comparison is made between these detection capabilities and the imaging requirements for the following medical applications: digital mammography, digital chest radiography and nuclear medicine. Experimental results and preliminary images are presented and discussed.

We present an autoradiography tool to be used mainly for genetic studies. It performs a quantitative analysis of radioactivity and can follow a dynamic process. We designed several applications, in particular one aimed at detecting hybridization of radio-labeled DNA fragments with known DNA-probes deposited on a micro-array. The technique is based on GaAs pixel array detector and low threshold, large dynamic range and good sensitivity integrated electronics developed for medical applications, suitable to detect markers (gamma or beta) such as 14C, 35S, 33P, 32P, 125I, even at very low activities. A Monte Carlo simulation of β− detection in GaAs is presented here in order to study the spatial resolution characteristics of such a system. For several biological applications, the electronics is required to perform at high temperatures (from 37° to 68°): we present here studies of noise and minimum threshold as a function of the temperature.

A GaAs pixel detector designed for digital mammography, equipped with a 36-channel single photon counting discrete read-out electronics, was tested using a test object developed for quality control purposes in mammography. Each pixel was 200×200 μm2 large, and 200 μm deep. The choice of GaAs with respect to silicon (largely used in other applications and with a more established technique) has been made because of the much better detection efficiency at mammographic energies, combined with a very good charge collection efficiency achieved thanks to new ohmic contacts. This GaAs detector is able to perform a measurement of low-contrast details, with minimum contrast lower (nearly a factor two) than that typically achievable with standard mammographic film+screen systems in the same conditions of clinical routine. This should allow for an earlier diagnosis of breast tumour masses. Due to these encouraging results, the next step in the evolution of our imaging system based on GaAs detectors has been the development of a VLSI front-end prototype chip (MEDIPIX ) in order to cover a much larger diagnostic area. The chip reads 64×64 channels in single photon counting mode, each one 170 μm wide. Each channel contains also a test input where a signal can be simulated, injecting a known charge through a 16 f F capacitor. Fake signals have been injected via the test input measuring and equalizing minimum thresholds for all the channels. On an average, in most of the performing chips available up to now, we have found that it is possible to set a threshold as low as 1800 electrons with an RMS of 150 electrons (10 standard deviations lower than the 20 keV photon signal roughly equivalent to 4500 electrons). The detector, bump-bonded to the chip, will be tested and a ladder of detectors will be prepared to be able to scan large surface objects.

A portable system has been developed for the control and the readout of a 64×64 pixel silicon hybrid detector (1.1×1.1 cm2 active area), bump-bonded to the Medipix1 readout chip. This system was originally designed for biomedial imaging applications and is based on standard commercial digital I/O boards and a compact dedicated interface (p-MUROS), connected to the portable PC. The Medipix1 chip is hosted in a 257 Pin Grid Array chip carrier directly placed on the p-MUROS board. This board is the simplified version of the MUROS1 readout board already developed in the framework of the Medipix collaboration. User-friendly software system (Medisoft 3.3) has been written to provide control of the system and image acquisition, display and processing. This complete hardware/software imaging system has been used with laboratory α, β and γ sources for test purposes and represents the portable version of a desktop imaging system developed for β-autoradiography. The system description and complete imaging tests are presented. Additional applications include the monitoring of the flux and the energy spectrum of X-rays tubes.

The double coincidence probability is a well known limitation to the rate capability of a 2-D detector with independent X- and Y-readout. The authors have implemented a parametric Monte Carlo simulation which could help in optimizing the double coincidence recovery. They have applied the parametric simulation to a specific 2-D solid state detector, they are developing for application in digital mammography.

We are investigating the feasibility of an intraoperative imaging probe for lymphoscintigraphy withTc-99m tracer, for sentinel node radioguided surgery, using the Medipix series of hybrid detectors coupled to a collimator. These detectors are pixelated semiconductor detectors bump-bonded to the Medipix1 photon counting read-out chip (64x64 pixel, 170 mm pitch) or to the Medipix2 chip (256x256 pixel, 55 um pitch), developed by the European Medipix collaboration. The pixel detector we plan to use in the final version of the probe is a semi-insulating GaAs detector or a 1–2mm thick CdZnTe detector. For the preliminary tests presented here, we used 300-um thick silicon detectors, hybridized via bump-bonding to the Medipix1 chip. We used a tungsten parallel-hole collimator (7mm thick, matrix array of 6464 100 mm circular holes with 170 um pitch), and a 22, 60 and 122 keV point-like (1mm diameter) radioactive sources, placed at various distances from the detector. These tests were conducted in order to investigate the general feasibility of this imaging probe and its resolving power. Measurements show the high resolution but low efficiency performance of the detector–collimator set, which is able to image the 122 keV source with

Mid-laser and microcurrent stimulation (MENS) have been found to be effective in the reduction of painful temporomandibular joints (TMJ) with internal derangement. There was significant improvement in mobility with the reduction of pain. Mid-laser was superior to MENS in its application and effect, and both were significantly better than the placebo treatment.

In the framework of the development of a digital radiography/autoradiography system using solid state detectors, we studied the performance of GaAs pixellated detectors regarding noise level and detection behavior of interpixel space. The detector is a 64×64 pixel array, 200 μm thick GaAs, 150 μm contact size and 20 μm interpixel space. Studies involve I – V curves, detector behavior for long-period biasing, noise as a function of temperature, and possible detection efficiency loss due to interpixel dead spaces.

The electrical characteristics of a LPE n-type GaAs crystal have been fully measured. The experimental results were used to build a model, including the parametrization of the electric field inside the crystal, and to study the features of such material as a detector in view of a possible application for digital radiography. The predictions of a Monte Carlo based on this model are in very good agreement with the measured performances of this crystal when used as a detector for X-rays in the diagnostic energy range.

Arthroscopic surgery of the temporomandibular joint is now being widely used for therapeutic, rather than diagnostic, benefits. However, there still remains a void in the literature as to the various rehabilitative protocols used on those patients who have undergone arthroscopy. This article presents a revision of techniques and procedures in the treatment and postoperative management of arthroscopic cases. This revision has been written after five years of experience and the treatment of approximately 300 cases.

Solid state detectors made of Si (4.8/spl times/8 mm/sup 2/) and GaAs (6.4/spl times/8 mm/sup 2/) pixel matrices bump-bonded to the Omega2 and Omega3 electronic read-out systems, developed at CERN for H.E.P. experiments, have been used to obtain autoradiographic images of clusters of human epithelial cells and DNA fragments separated via electrophoresis, both labeled with /sup 32/P. The system has shown a good minimum detectable activity per unit area of 2.10/sup -4/ cps mm/sup -2/, and has proved linear for a count rate in the range 0.2-20 cpa, typical of autoradiography. The pixel dimensions are 75/spl times/500 /spl mu/m/sup 2/ (Si-Omega2) and 50/spl times/500 /spl mu/m/sup 2/ (GaAs-Omega3), respectively. We are able to clearly localize clusters of cells which have incorporated the radioactive tracer and DNA fragments on an electrophoretic gel on paper (blots).

Gallium arsenide pixel detectors processed on a 200 mu m Semi-Insulating (SI) Hitachi substrate were bump-bended to the Omega3 electronics developed at CERN for high energy physics [1]. The pixel dimensions are 50 mu m x 500 mu m for a total of 2048 cells and an active area of similar to 0.5 cm(2). Our aim is to use this system for medical imaging. We report the results obtained after irradiation of the detector with different X-ray sources on phantoms with different contrasts. The system showed good sensitivity to X-rays from Am-241 (60 keV) and Cd-109 (22.1 keV). It is also sensitive to p-particles from Sr-90 as well as from P-32 which is used as a tracer for autoradiography applications. The inherent high absorption efficiency of GaAs associated with the self-triggering capabilities of the pixel readout system reduced considerably the acquisition time compared with traditional systems based on silicon or emulsions. The present configuration is not optimised for X-ray imaging. The reduction of the pixel dimensions to 200 mu m x 200 mu m together with the integration of a counter in the pixel electronics would make the detector competitive for applications like mammography or dental radiology. For certain applications in biochemistry, such as DNA sequencing, where good spatial resolution is required only in one direction, the present setup should allow the best spatial resolution available up to now with respect to other digital autoradiographic systems. DNA sequencing tests are now under way.

We describe a VLSI-based processing system performing X - Y coincidence at a very high rate in the synchronous mode. The processor has been designed for applications in digital mammography with two-sided μ-strip silicon detectors but can be used to provide the computational section of any imaging system that needs fast coincidence. The VLSI chip has been successfully tested on a 32 + 32 channels DAQ chain.

The authors have developed a TDC+Transputer-based acquisition system to study the X-ray imaging capabilities of a silicon /spl mu/-strip detector with 100 and 200 /spl mu/m read-out pitch. This system allows real-time image acquisition and display. The authors present images obtained with an X-ray mammography tube using sub-millimeter high contrast test objects on a 16*16 channels prototype. >

We have developed a technique and a prototype for /spl beta/-rays and /spl gamma/-rays quantitative imaging of biological samples which have been radioactively labeled. The prototype is based on a solid state pixel detector, bump-bonded to a low threshold, single particle counting chip: the detector we used is 200-/spl mu/m thick GaAs, with pixel size 170 /spl mu/m. In this paper we describe an experiment that shows the capability of monitoring a dynamic process. Specifically, [/sup 14/C]L-Leucine uptake by eggs of mollusk cephalopod Octopus vulgaris and the consequent migration of marker into the ooplasm was followed.

We present some additional results obtained with the BETAview system, a digital system for real time /spl beta/-imaging based on semiconductor pixel detectors and on a single photon counting read-out chip. In this paper, we describe the system assembled with a Si detector, 300 /spl mu/m thick, segmented into 64/spl times/64 square pixels with 170 /spl mu/m pitch. The solid state pixel array detector is bump-bonded pixel by pixel to a low threshold, single particle counting electronics, the photon counting chip (PCC) developed by the Medipix1Collaboration for biomedical applications. Each cell (corresponding to a detector pixel) of the front-end chip has a maximum count rate of 2 MHz, a minimum nominal threshold of 1400 e~ (corresponding to about 5 keV in Si) and contains a 15-bit counter. The detector sensitive area is about 1 cm/sup 2/, but several detectors could be assembled in arrays. The measured background counts were about 3.5/spl middot/10/sup -2/ cps/cm/sup 2/, which implies a very high sensitivity of the device. The detection threshold used in this experiment was 15 keV. In this paper we show the results obtained in the real time monitoring of two biological dynamic processes: an amino acid uptake and the thermal denaturation process of oligonucleotides. Specifically, we have followed over time the accumulation of a marked amino acid ([/sup 14/C]L-Leucine) into Octopus vulgaris eggs cells. After about 20 min from the beginning of the uptake process, the radioactively marked eggs become clearly visible over the background culture radioactive medium. We also describe the successful performance of the /spl beta/-imaging system in genetic studies involving the real time reconstruction of denaturation and kinetics curves for two different /sup 32/P-radiolabeled nucleotides.

We present some additional results obtained with the BETAview system [1], a digital system for real time beta-imaging based on semiconductor pixel detectors and on a single photon counting read-out chip. In this paper, we describe the system assembled with a Si detector, 300-mum thick, segmented into 64 x 64 square pixels with 170-mum pitch. The solid-state pixel array detector is bump-bonded pixel by pixel to a low threshold, single particle counting electronics, the photon counting chip (PCC) developed by the Medipix1 Collaboration for biomedical applications. Each cell (corresponding to a detector pixel) of the front-end chip has a maximum count rate of 2 MHz, a minimum nominal threshold of 1400 e(-) (corresponding about 5 keV in Si), and contains a 15-bit counter. The detector sensitive area is about 1 cm(2), but several detectors could be assembled in arrays. The measured background counts were about 3.5 x 10(-2) cps/cm(2), which implies a very high sensitivity of the device. The detection threshold used in this experiment was similar to15 keV. In this paper, we show the results obtained in the real-time monitoring of two biological dynamic processes: an amino acid uptake by living cells and the thermal denaturation process of oligonucleotides. Specifically, we have followed over time the accumulation of a marked amino acid ([C-14]L-Leucine) into Octopus vulgaris eggs cells. The results, described in Section III-B, show that after about 20 min from the beginning of the uptake process, the radioactively marked eggs become clearly visible over the background culture radioactive medium. In Sections III-C and III-D, we also describe the successful performance of the beta-imaging system in genetic studies involving the real time reconstruction of denaturation and kinetics curves for two different P-32-radiolabeled nucleotides.

We present the results of a test with a prototype apparatus aimed to detect the ultraviolet Cherenkov light in the wavelength range 2000–2300 A, emitted by high energy cosmic ray showers. The system consists of a gas proportional chamber, with TMAE vapour as the photosensitive element, placed on the focal plane of a 1.5 m diameter parabolic mirror. The test was done during the summer of 1989 with cosmic ray showers seen in coincidence with the EAS-TOP experiment, an extended atmospheric shower charged particle array now being exploited at Campo Imperatore, 1900 m above sea level, on top of the Gran Sasso underground Laboratory of INFN. The results were positive and show that a full scale ultraviolet Cherenkov experiment with good sensitivity, angular resolution and virtually no background from moonlight or even daylight can be envisaged.

An experimental technique is presented to determine the effectiveness of methods to tag photon initiated air showers and reject hadron initiated ones. The technique is based on the rate reduction in the Moon direction. With a photon energy threshold below or equal to 1 TeV, with an angular resolution of a few mrad and being insensitive to visible light, the proposed CLUE detector allows a wide and original physics program. In particular the direct measurement of the fraction of primary photons in the continuum of the cosmic ray flux is feasible with adequate statistics in a few months of data taking.

Semi-insulating gallium arsenide (SI-GaAs) detectors, in the form of Schottky diodes, have been irradiated from the front or from the back contact or from the side, with light pulses from picosecond laser source, tunable in the range of 780–1020 nm and focused to a 50–100 μm spot on the surface of the detector. Energy per pulse was in the range of 4–25 pJ, with a 10 or 100 Hz repetition rate. Each pulse mimics the interaction of a single energetic particle with the substrate, but with a photon mean free path modulated in the range of 1 μm–1 cm, depending on the light wavelength. The SI-GaAs substrates have a thickness of 200 μm (VGF grown), or 600 μm (LEC) or 1000 μm (VGF). The time response of the detectors, analysed with the Transient Current Technique (using a fast digital sampling oscilloscope) in terms of peak signal amplitude and charge rise time, has been evaluated as a function of: reverse voltage bias (50–1200 V), light wavelength (780–1020 nm), side position between the electrodes, position on the front contact. The results are: (1) the shape of the transient current signal may show the presence of two peaks, about 1 ns apart; (2) the charge rise time, considered to be dominated by the charge collection time, is between 2 and 13 ns; (3) the charge rise time, as due to electron drift or hole drift in the region between the contacts, has been measured as 2–5 ns, also dependent on the applied bias; (4) the transient current (exponential) decay time, for front or back irradiation, increases with the bias voltage up to 2–20 ns and these data are considered to be consistent with the electron detrapping time; (5) under reverse bias, for 1 mm pad side and a large ohmic contact on the back, the electric field extends around the front contact up to about 200 μm.

We present an autoradiography system (BETAview) for a quantitative analysis of radioactive markers in biological samples; this system is also able to monitor a dynamic process. It is based on a solid-state pixel array detector, bump bonded to low threshold, integrated electronics developed for medical applications (Medipix). The present assembly is equipped with a 200 μm thick GaAs square detector, about 1 cm side, segmented into 64×64 170-μm size square pixels; simulation and experimental studies show good linearity and high sensitivity to β sources. Imaging tests with β sources of medical and biological interest such as 14C, 35S, 32P are reported.

Thiscollaborationhasalreadyobtainedencouragingresultsabouttheperformanceof200and600mmthicksemi-insulatingGaAsdetectors,intermsofchargecollectionefficiency(c.c.e.),detectionefficiencyandimagingcapabilities,tobeusedassinglephotoncountingdetectorswithphotonsintheradiographicenergyrange.Thepossibleuseofsuchdetectorsinnuclearmedicineimpliesdetectionofmoreenergeticphotons,uptothe140keVofthe 99m Tcsource;thusefficientdetectorsmustbethickerthanthosepreviouslystudied.Inthispaper,wepresenttheresultsoftheinvestigationofelectricalanddetectionproperties(spectra,c.c.e.,energyresolution)ofaseriesofdetectors,whosethicknessrangesfrom 200to1000mm, when irradiated with radioactive sources over the energy range used in nuclear medicine.# 2001 ElsevierScienceB.V.Allrightsreserved. 1. IntroductionIn nuclear medicine, in applications as scinti-graphy and single photon emission computedtomography(SPECT)thephotonstobedetectedare emitted by a radioisotope present into thepatient thanks to a radiopharmaceutical (radio-isotope-taggedcompound),whichcanbeinjected,ingested or breathed [1], in order to ‘‘trace’’variousfunctionsofthebody.Oneoftheprimaryadvantages associated with the use of radionu-clides is the large signal (the emitted radiation)obtainedfromtherelativelysmallmassofradio-nuclide employed for a given study. The minutemass of the radiolabeled material allows for theobservation without disturbance of the systemunder study through pharmacological or toxico-logicaleffect.Thephysicalcharacteristicsofradio-nuclides that are desirable for nuclear medicineimaginginclude:asuitablephysicalhalf-life;decayvia photon emission; associated photon energyhigh enough to penetrate the body tissue withminimal tissue attenuation and low enough toallowingforminimalthicknessofcollimatorsepta;absenceofparticulateemission.

The performance of semi-insulating GaAs detectors, grown with the LEC technique, has been studied by irradiating the Schottky diodes with 2 and 2.4 MeV monoenergetic protons in a pencil beam with sub-millimeter width (70 or 600 μm). The beam was moved across the surface of the front (Schottky) contact, in order to investigate the uniformity of the detection characteristics over the sensitive area of the diodes, and to study the electric field behavior around the Schottky contact. For each scanning position, a pulse-height spectrum was measured. Then, the charge collected and the energy resolution were obtained as a function of the irradiation position both on the contact and outside it. The data show that • the best spectroscopic response occurs for the beam with 70 μm width, • when the beam is incident onto the contact, the energy resolution is between 1% and 5%, and the variation of the charge collected, for different irradiation position, is less than 30%, • when the beam is incident onto the border of the contact (substrate is irradiated), the spectrum is degraded and no clear peak is present, • collection of charge still occurs at distances up to about 500 μm from the border of the Schottky contact (for a pixel size of 200 μm), or up to about 200 μm (for a pixel diameter of 3 mm), • saturation of the curve collected charge vs. reverse bias voltage occurs at about 100 V for both 2 MeV (range=32 μm) and 2.4 MeV protons (range=41 μm).

Current pulses produced by absorption of picosecond near-infrared light pulses have been used in order to analyze the shape of the electric field and charge transport properties in semi-insulating (SI) GaAs Schottky barrier X- and gamma-ray detectors. Diodes with square pads of side 0.2–1 mm on 200, 600 and 1000-μm-thick SI GaAs substrates have been illuminated from the front (Schottky) contact, from the back (ohmic) side and laterally between the contacts. Current pulses have been recorded with a fast digital sampling oscilloscope, at room temperature, without using any signal amplification. Current and charge pulse shapes have been analyzed as a function of reverse bias voltage, positioned on the detector surface and optical wavelength around the near-infrared absorption edge of GaAs. The wavelength tuning allows for increasing light penetration lengths. Signal analysis gives the peak current, total collected charge and the charge collection time, which are related to the average strength of the electric field and the drift velocity field, while pulse shape depends on the local value of these fields. The experimental results show that a complete detector characterization is feasible with this optical technique, in a manner analogous to that commonly done with gamma- or X- or alpha-ray sources, with the advantage of analyzing the charge collection time. An additional advantage is represented by focusing the light beam on the detector surface, for 1D or 2D scan.

Description of a hardare and software tool for simulation of the response of a silicon detectors to photons in the diagnostic energy range.

A system has been developed for the control and readout of an electronic circuit (Medipix) designed for medical X-ray imaging applications. This system (MUROS-1) is based on standard commercial analogue and digital I/O boards and a simple dedicated interface. User-friendly software (Medisoft 3) has been developed to provide full control of the system, including fine tuning of the Medipix circuit, image presentation and post-exposure image processing.

We made a characterisation of GaAs detectors with an epitaxial p-type layer deposited on the 200 /spl mu/m semi-insulating substrate. The charge collection efficiency for 60-keV photons and 5.49 MeV alpha particle depends on the doping level of the p-layer. When completely depleted (reverse bias >200-300 V), the collected charge can be greater than 100%, implying the presence of some charge gain mechanism. At the same reverse bias and doping concentration, the collected charge depends also on the size of the contact pad. Moreover, the lower the p-doping, the lower the current density. The present findings confirm our previous work, obtaining gains up to 4:1.

We studied pixel radiation detectors for X-ray radiography based on semi-insulating GaAs: in particular, we investigated both annealed and non-annealed contact deposition techniques for the ohmic contact and both ring-guarded and non-guarded Schottky contact, in order to reduce the leakage current and to increase the maximum applied electric field. Spectroscopic characterization with a 60 keV 241 Am source has been performed. Among these different detectors, the CCE can reach 99±6%, while the energy resolution Δ E / E can go down to 4.1±0.2%.

GaAs optoelectronic switches as local control of the HV MSGCs strips are being developed for the CMS experiment. The radiation environment inside the CMS tracker will be very high. Typical hadron fluence will be up to +1014 cm~2 and ionising doses as large as 100 kGy during the experiment lifetime. The aim of this work is to test the performance of some GaAs devices in terms of radiation hardness up to the levels of hadron fluence and ionising doses expected inside the CMS tracker. ( 1999 Elsevier Science B.V. All rights reserved.

In this paper we present the results of an experimental study concerning different contact deposition processes on Semi-Insulating (S.I.) GaAs detectors aiming to study and optimize their performance in terms of leakage current, break-down voltage, charge collection efficiency and energy resolution when irradiated with 60 KeV photons; in particular the effect of the mesa etching treatment on the Schottky barrier side of the detectors has been studied. Such treatment certainly improves the detector performances related to the very important issue of the electric field uniformity. Detectors with satisfactory features in view of their possible application to Digital Radiography have been obtained.

Nausea and vomiting caused by motion sickness are serious and sometimes debilitating symptoms for commercial and recreational seafarers.In order to treat these symptoms, a portable device, the Relief Band, was designed to deliver acustimulation to the Neiguan (P6) acupuncture point.Nine volunteers used the device on a placebo point or the P6 active point on the open seas outside the San Francisco Bay. Motion sickness symptoms were graded from 1 ("feel fine") to 5 ("intermittent vomiting, with or without nausea").Five subjects with motion sickness initially positioned the device at the placebo site and reported minimal symptom improvement (3.6 +/- 0.6 to 3.4 +/- 1.1) (mean, +/- SD), whereas the other four subjects initially used the device in the P6 position and reported decreased symptoms (4.3 +/- 1.0 to 1.0 +/- 0.2). The position of the Relief Band was then switched; in the four subjects who switched to the placebo position, symptoms worsened (1.0 +/- 0.2 to 4.0 +/- 1.4); whereas, in the five subjects where the device was switched to the P6 position, symptoms improved in each subject (3.4 +/- 1.1 to 1.0 +/- 0.7) (p0.01).Motion sickness symptoms were suppressed by portable acustimulation in field studies of seasickness. The Relief Band may be an alternative to drug treatments of the nausea and vomiting of seasickness.

GaAs is a semiconductor suitable for room temperature X-ray detection but hitherto has suffered from incomplete charge collection and is affected by noise. Recent GaAs detectors made with LEC material have shown improved charge collection efficiency and energy resolution. In this paper we describe the fabrication process and present the results obtained with 80 μm thick pad detectors.

Laser therapy has been found effective in the management of pain associated with rheumatoid and degenerative joint arthritis and disease. The efficacy of mid-laser therapy has been tested specifically on patients with degenerative joint disease (DJD) involving the temporomandibular joint (TMJ). The following controlled clinical study was designed to test the efficacy of mid-laser therapy to placebo therapy in the reduction of pain associated with TMJ disorders specific to arthralgic DJD.

In order to investigate the correlation between the electrical characteristics of the semi-insulating GaAs and its properties as a possible detector for low energy gamma-rays, we have measured, for various materials, the forward and the reverse I-V characteristic, the capacitance as a function of the frequency at various bias voltages and the capacitance as a function of the bias voltage at various frequencies. To measure the charge collection efficiency, the energy resolution and the detection efficiency as a function of the bias voltage the crystals have been irradiated with 22, 60, 88 and 122 keV photons. The results are discussed and a comparison between materials from various factories, of different thickness and equipped with different contacts is also presented. >

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.

This study examined the effect of sensory affect stimulation (SAS) delivered through the volar surface of the wrist on pregnancy-induced nausea and vomiting. Twenty-three women with significant nausea and vomiting in the first 14 weeks of pregnancy were enrolled in a randomized, crossover study comparing an active SAS unit and an inactive placebo unit. Twenty-one women experienced improvement in symptoms, 20 (87%) with the SAS unit and 10 (43%) with the placebo device. Nine women had an improvement with both devices. Eleven women reported an improvement with SAS only, while one woman had placebo improvement only. SAS applied to the wrist can effectively improve pregnancy-induced nausea and vomiting as compared to a placebo device.

Double-sided microstrip silicon crystals are being tested as detectors for X-rays in the diagnostic energy range (10-100 keV) for digital radiology. An analog-to-digital-converter and CAMAC based acquisition system has been developed to study the imaging capabilities of a silicon microstrip detector with 100 and 200 mu m read-out pitch. The authors present the first images of submillimeter high-contrast phantoms obtained with an X-ray mammography tube operating at high flux density. A preliminary contrast transfer function study was performed; a low frequency contrast of about 0.97 for a high-contrast phantom and a decrease of contrast at a frequency of 5 1p/mm corresponding to the detector intrinsic spatial resolution (100 mu m) were measured. >

The authors have developed a TDC+transputer-based acquisition system to study the X-ray imaging capabilities of a silicon μstrip detector with 100 and 200 μm read-out pitch. This system allows real-time image acquisition and display. The authors present images obtained with an X-ray mammography tube using sub-millimeter high contrast test objects on a 16*16 channels prototype

In the framework of an experimental program to study the possibility of using a silicon crystal for X-ray detection in the diagnostic energy range (10-100 keV), the authors present the first experimental results obtained with a silicon detector (300 mu m thick, 1.4*1.4 cm2 surface) with microstrips deposited on each side: 25 mu m spacing on the junction side and 50 mu m spacing on the ohmic side: 25 mu m spacing on the junction side and 50 mu m spacing on the ohmic side; the read-out pitch is 100 mu m for both sides. Energy and spatial resolutions have been measured by means of collimated radioactive sources: 241Am (E gamma =60 keV) and 109Cd (E gamma =24 and 88 keV). A very good linearity in the response to the photon energy has been measured. Tantalum wires, i.e. high contrast objects, have been used as phantoms when exposing the detector to the 60 keV photons; the authors present the images thus obtained.

In the framework of an experimental study of the possibility of using a double-sided silicon strip detector for digital radiography, and electronic system has been developed to make the signals coming from the two sides of the crystal coincide and hence to define the impact point of X-rays, giving an image matrix as final output. It is based on commercial PALs, and has been built and tested for 32×32 channels. In this configuration the dead time between two subsequent events is ⩽34 ns. Its logic is easily extendable to a large number of channels with a limited increase of the overall dead time and its various stages have been devised in view of a future integration as VLSI