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Chemical Vapor Deposited (CVD) polycrystalline diamond has been proposed as a radiation-hard alternative to silicon in the extreme radiation levels occurring close to the interaction region of the Large Hadron Collider. Due to an intense research effort, reliable high-quality polycrystalline CVD diamond detectors, with up to 270 μm charge collection distance and good spatial uniformity, are now available. The most recent progress on the diamond quality, on the development of diamond trackers and on radiation hardness studies are presented and discussed.

SUCIMA (Silicon Ultra fast Cameras for electron and γ sources In Medical Applications) is a project approved by the European Commission with the primary goal of developing a real time dosimeter based on direct detection in a Silicon substrate. The main applications, the detector characteristics and technologies and the data acquisition system are described.

CVD diamond material was used to build position-sensitive detectors for single-charged particles to be employed in high-intensity physics experiments. To obtain position information, metal contacts shaped as strips or pixels are applied to the detector surface for one- or two-dimensional coordinate measurement. Strip detectors 2×4 cm2 in size with a strip distance of 50 μm were tested. Pixel detectors of various pixel sizes were bump bonded to electronics chips and investigated. A key issue for the use of these sensors in high intensity experiments is the radiation hardness. Several irradiation experiments were carried out with pions, protons and neutrons exceeding a fluence of 1015 particles/cm2. The paper presents an overview of the results obtained with strip and pixel detectors in high-energy test beams and summarises the irradiation studies.

A novel Monolithic Active Pixel Sensor (MAPS) for charged particle tracking made in a standard CMOS technology is proposed. The sensor is a photodiode, which is readily available in a CMOS technology. The diode has a special structure, which allows the high detection efficiency required for tracking applications. The partially depleted thin epitaxial silicon layer is used as a sensitive detector volume. Semiconductor device simulation, using either ToSCA based or 3-D ISE-TCAD software packages shows that the charge collection is efficient, reasonably fast (order of 100 ns), and the charge spreading limited to a few pixels only. A first prototype has been designed, fabricated and tested. It is made of four arrays each containing 64×64 pixels, with a readout pitch of 20 μm in both directions. The device is fabricated using standard submicron 0.6 μm CMOS process, which features twin-tub implanted in a p-type epitaxial layer, a characteristic common to many modern CMOS VLSI processes. Extensive tests made with soft X-ray source ( 55 Fe) and minimum ionising particles (15 GeV/ c pions) fully demonstrate the predicted performances, with the individual pixel noise (ENC) below 20 electrons and the Signal-to-Noise ratio for both 5.9 keV X-rays and Minimum Ionising Particles (MIP) of the order of 30. This novel device opens new perspectives in high-precision vertex detectors in Particle Physics experiments, as well as in other application, like low-energy beta particle imaging, visible light single photon imaging (using the Hybrid Photon Detector approach) and high-precision slow neutron imaging.

Diamond based pixel detectors are a promising radiation-hard technology for use at the LHC. We present first results on a CMS diamond pixel sensor. With a threshold setting of 2000 electrons, an average pixel efficiency of 78% was obtained for normally incident minimum ionizing particles.

In this article we present the performance of recent chemical vapour deposition (CVD) diamond micro-strip sensors in beam tests. In addition, we present the first comparison of a CVD diamond micro-strip sensor before and after proton irradiation.

The ability of HgI2 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 HgI2 crystal to its impurity content and stoichiometry. These quantities determine the detector grade that may be achieved using that starting material. Nine different HgI2 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.

Potentially low cost and large area polycrystalline mercuric iodide room-temperature radiation detectors, with thickness of 100–600 μm have been successfully tested with dedicated low-noise, low-power mixed signal VLSI electronics which can be used for compact, imaging solutions. The detectors are fabricated by depositing HgI 2 directly on an insulating substrate having electrodes in the form of microstrips and pixels with an upper continuous electrode. The deposition is made either by direct evaporation or by screen printing HgI 2 mixed with glue such as Poly-Vinyl-Butiral. The properties of these 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. The detectors which act as radiation counters have been tested with a beta source as well as in a high-energy beam of 100 GeV muons at CERN, connected to VLSI, low noise electronics. Charge collection efficiency and uniformity have been studied. The charge is efficiently collected even in the space between strips indicating that fill factors of 100% could be reached in imaging applications with direct detection of radiation. Single photon counting capability is reached with VLSI electronics. These results show the potential of this material for applications demanding position sensitive, radiation resistant, room-temperature operating radiation detectors, where position resolution is essential, as it can be found in some applications in high-energy physics, nuclear medicine and astrophysics.

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.

The paper reviews measurements of the radiation hardness of CVD diamond for 24 GeV/c proton irradiation at fluences up to 5 ∗ 10 15 protons/cm 2 . The results not only show radiation damage but also an annealing effect that is dominant at levels around 10 15 protons/cm 2 . A model describing both effects is introduced, enabling a prediction of the distribution curve of the charge signal for other levels.

In future HEP accelerators, such as the LHC (CERN), detectors and electronics in the vertex region of the experiments will suffer from extreme radiation. Thus radiation hardness is required for both detectors and electronics to survive in this harsh environment. CVD diamond, which is investigated by the RD42 Collaboration at CERN, can meet these requirements. Samples of up to 2×4 cm 2 have been grown and refined for better charge collection properties, which are measured with a β source or in a testbeam. A large number of diamond samples has been irradiated with hadrons to fluences of up to 5×10 15 cm −2 to study the effects of radiation. Both strip and pixel detectors were prepared in various geometries. Samples with strip metallization have been tested with both slow and fast readout electronics, and the first diamond pixel detector proved fully functional with LHC electronics.

CVD diamond radiation sensors are being developed for possible use in trackers in the LHC experiments. The diamond promises to be radiation hard well beyond particle fluences that can be tolerated by Si sensors. Recent results from the RD 42 collaboration on charge collection distance and on radiation hardness of CVD diamond samples will be reported. Measurements with diamond tracking devices, both strip detectors and pixel detectors, will be discussed. Results from beam tests using a diamond strip detector which was read out with fast, 25 ns shaping time, radiation-hard pipeline electronics will be presented.

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.

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/ particle's 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.

Microstrip gas chambers made from high resistivity substrates are often plagued by gain losses. A model of surface charging coupled to precise electrostatic simulations, which reveal details of electric fields close to the substrate surface, suggests how stable gains can be achieved nevertheless. Measurements support these considerations.

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.

A high speed data acquisition system was used to record events from sulphur-nucleus collisions at 200 GeV/c per nucleon at the CERN NA36 experiment. The system was designed to accept up to 12 Mbytes of raw data per beam spill. A multicrate Fastbus-CAMAC system was used to acquire the data during the beam spill and thereafter event-building and transfer to IBM 3480 cartridges were accomplished by means of two processors in a VME crate which processed data between spills. Communication between Fastbus and VME crates was provided by a fast link developed at CERN. © 1992.

LEPSI; The SUCIMA collaboration has been developing instruments and methods for real-time, high granularity imaging of extended electron sources. In particular, dosimetry of intravascular brachytherapy β sources has been intensively studied, together with monitoring of hadrontherapy beams by imaging of secondary electrons emitted by a non-disruptive target. The paper reports the latest results on absolute dosimetry with a large-area silicon strip detectors and on beam monitoring with a hybrid pad sensor.

Progress in experimental particle physics in the coming decade depends crucially upon the ability to carry out experiments in high-radiation areas. In order to perform these complex and expensive experiments, new radiation hard technologies must be developed. This paper discusses the use of diamond detectors in future tracking applications and their survivability in the highest radiation environments. We present results of devices constructed with the newest polycrystalline and single crystal Chemical Vapor Deposition diamond and their tolerance to radiation.

LEPSI; SUCIMA (Silicon Ultra fast Cameras for electron and γ sources In Medical Applications) is a project approved by the European Commission within the Fifth Framework Programme, with the primary goal of developing a real time dosimeter based on direct detection of ionising particles in a position sensitive Silicon sensor. The main applications of this device are imaging of intravascular brachytherapy radioactive sources with activities up to 3 GBq and real time monitoring of hadrontherapy beams. In order to perform a feasibility study, during the first two years a real time dosimeter has been engineered using Silicon microstrip detectors read out by an integrating dead-timeless front-end electronics. The prototypes have been qualified as relative dosimeter with respect to certified secondary standards; moreover, further measurements are on going in order to investigate the possibility to use the sensors as absolute dosimeters. Since the final device is supposed to provide a two dimensional image, two different Monolithic Active Pixel dosimeters have been designed and produced by the collaboration based on CMOS and Silicon On Insulator technologies. The main features of the two sensors are presented in this paper.

Real-time dosimetry is a critical issue in most radiotherapy applications. Silicon Ultra fast Cameras for electron and gamma sources In Medical Applications (SUCIMA) is a project addressing the development of an imaging system of extended radioactive sources based on monolithic and hybrid position-sensitive silicon sensors, where “imaging” has to be intended as the record of a dose map. The detector characteristics are constrained by the main applications, namely brachytherapy and real-time monitoring of a hadron beam for oncology. The key issues in the sensor and DAQ development are described together with the most relevant medical applications. SUCIMA 1 is a project approved by the EC within the V Framework Program.

Chemical vapor deposition diamond has been discussed extensively as an alternate sensor material for use very close to the interaction region of the LHC where extreme radiation conditions exist. During the last few years diamond devices have been manufactured and tested with LHC electronics with the goal of creating a detector usable by all LHC experiment. Extensive progress on diamond quality, on the development of diamond trackers and on radiation hardness studies has been made. Transforming the technology to the LHC specific requirements is now underway. In this paper we present the recent progress achieved.

Diamond is a promising sensor material for future collider experiments due to its radiation hardness. Diamond pixel sensors have been bump bonded to an ATLAS pixel readout chip using PbSn solder bumps. Single chip devices have been characterised by lab measurements and in a high-energy pion beam at CERN. Results on charge collection, spatial resolution, efficiency and the charge carrier lifetime are presented.

Radiation detectors have been fabricated from very thick films (100-600 /spl mu/m) of mercuric iodide (HgI/sub 2/). These devices, which function as nuclear particle counters and not as spectrometers, have been prepared with single continuous electrical contacts, linear microstrips and square pixel contacts. The word ceramic is used to distinguish the detectors from single crystals which are usually studied for this application. The detectors have been tested with different kinds of gamma and beta sources as well as in a high energy beam of 100 GeV muons at CERN. The presented results show the potential of this material for applications demanding position sensitive, radiation resistant, room-temperature operating radiation detectors, where position rather than spectroscopic resolution is essential, as it can be found in some specific applications in high energy physics, nuclear medicine and astrophysics. Because of the low cost and of the polycrystallinity, detectors can be potentially fabricated in any size and shape, using standard ceramic technology shaping equipment, which is an attractive feature where low cost and large area applications are needed.

A monolithic active pixel sensor (MAPS) for charged particle tracking based on a novel detector structure was proposed, simulated, fabricated and tested. The detector designed accordingly to this idea is inseparable from the readout electronics, since both of them are integrated onto the same, standard for a CMOS process, low-resistivity silicon wafer. The individual pixel is comprised of only 3 MOS transistors and a photodiode collecting the charge created in a thin undepleted epitaxial layer. This approach provides the whole detector surface sensitive to radiation (100% fill factor) with reduced pixel pitch(very high spatial resolution). This yields a low cost, high resolution and thin detecting device. The detailed device simulations using an ISE-TCAD package have been carried out in order to study a charge collection mechanism and to validate the proposed idea. Consequently, two prototype chips have been fabricated using 0.6 /spl mu/m and 0.35 /spl mu/m CMOS processes. Special radiation tolerant layout techniques were used in the second chip design. Both chips were tested and fully characterised. The pixel conversion gain was calibrated using 5.9 keV photons and prototype devices were exposed to the 120 GeV/c pion beams at CERN. Obtained results preceded by general design ideas and simulation results are reviewed.

The paper gives new results on the radiation tolerance of CVD diamond for irradiation with 300 MeV/c pions and 24 GeV/c protons. The measured charge signal spectrum is compared at several irradiation levels with the spectrum calculated by a model. Irradiation by particles causes damage leading to a decrease of the charge signal. However, both the measurements and the outcome from the model show that for tracker applications this drawback is at least partly counterbalanced by a narrowing of the distribution curve of the charge signal. As a result, the efficiency of a CVD diamond tracker is less affected by irradiation than the mean charge signal.

A new generation of semi-conducting pixel sensors for detecting minimum ionising particles (m.i.p.) was designed and first prototypes of Monolithic Active Pixel Sensors (MAPS), called MIMOSA, 2 were fabricated in a standard CMOS technology. The performances of the first prototypes were evaluated with high energy π− beams and with an X-ray source in strong magnetic fields. The beam test results demonstrate that the sensors detect m.i.p.s with very high efficiency and signal-to-noise ratio and provide excellent spatial resolution. The influence of strong magnetic fields is observed to be modest.

A novel monolithic active pixel sensor for charged particle tracking has been designed and fabricated in a standard CMOS technology. The device architecture is identical to a CMOS camera, recently being proposed as an alternative to CCD sensors for visible light imaging. The partially depleted thin epitaxial silicon layer is used as a sensitive detector volume. The sensor is a photodiode having a special structure, which allows the high detection efficiency required for tracking applications A first prototype was made of four arrays each containing 64×64 pixels, with a readout pitch of 20 μm in both directions. An architecture allowing serial readout of the analogue information from each pixel has been implemented. To evaluate the tracking performance of such a device, series of tests have been performed using a high-energy particle beam. A detailed analysis of the beam test data presented in this work demonstrate close to 100% minimum ionising particle detection efficiency and a good enough signal-to-noise ratio of more than 30.

A preliminary study of the charge collection in the recently proposed Monolithic Active Pixel Sensor devices for minimum ionising particles tracking is presented. The baseline pixel architecture is similar to a visible light CMOS camera, emerged as a competitor to widespread CCDs. Free electrons created by an impinging particle are collected by a photodiode from a thin partially depleted epitaxial silicon layer allowing 100% of fill-factor. Such a structure is fabricated using standard CMOS process. The sensor and associated readout electronics are integrated onto the same wafer, resulting in a low cost, high resolution and possibly thin detector. The crucial points of a CMOS detector are the time and the efficiency of the charge collection. These factors, in spite of undeniable advantages of CMOS detectors, can limit their performances. The detailed 3-D simulations using commercially available ISE-TCAD package are carried out in order to study a charge collection process. Although it is dominated by thermal diffusion, more than 1000 electrons are collected in the 3×3 pixels cluster within a time of 100 ns in a 15 μm thick epitaxial layer. Simulation results are compared to measurements performed on the prototype APS CMOS MIMOSA using either a fast Infrared (IR) laser or a high-energy particle beam as an excitation source.

CVD diamond detectors are of interest for charged particle detection and tracking due to their high radiation tolerance. In this article, we present, for the first time, beam test results from recently manufactured CVD diamond strip detectors and their behavior under low doses of electrons from a β-source and the performance before and after intense (>10 15 /cm 2 ) proton- and pion-irradiations. We find that low dose irradiation increase the signal-to-noise ratio (pumping of the signal) and slightly deteriorate the spatial resolution. Intense irradiation with protons 2.2×10 15 p / cm 2 lowers the signal-to-noise ratio slightly. Intense irradiation with pions 2.9×10 15 π / cm 2 lowers the signal-to-noise ratio more. The spatial resolution of the diamond sensors improves after irradiations.

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).

Diamond is a nearly ideal material for detecting ionising radiation. Its outstanding radiation hardness, fast charge collection and low leakage current allow it to be used in high radiation environments. These characteristics make diamond sensors particularly appealing for use in the next generation of pixel detectors. Over the last year, the RD42 collaboration has worked with several groups that have developed pixel readout electronics in order to optimise diamond sensors for bump-bonding. This effort resulted in an operational diamond pixel sensor that was tested in a pion beam. We demonstrate that greater than 98% of the channels were successfully bump-bonded and functioning. The device shows good overall hit efficiency as well as clear spatial hit correlation to tracks measured in a silicon reference telescope. A position resolution of 14.8 μm was observed, consistent with expectations given the detector pitch.

This paper reviews the development of CVD diamond pixel detectors. The preparation of the diamond pixel sensors for bump-bonding to the pixel readout electronics for the LHC and the results from beam tests carried out at CERN are described.

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.

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.

The direct deposition of polycrystalline semiconductor HgI 2 detectors on pre-deposited specially designed pixel electrodes is described, using two methods, the hot wall vapor deposition, HWVD, and thick film screen print (SP) methods. Some characterization results of the HgI 2 material used to facilitate the detectors are described. The pre-deposited substrate is made by standard hybrid technology. The electrode pattern is a 16*16 pixel square pattern each with a size of 1.48 mm and with 0.1 mm spacing; the total area covered by the pixels is (25.28 mm) 2 equals 639.078 mm 2 . In order to fan out the pixels to read-out electronics, holes were made through the ceramic thickness and connecting lines were drawn on the opposite side of the ceramic alumina substrate, where complicated patterns can be produced. The pixel detector is tested with beta particles, and data showing the leakage current vs. bias, are given showing a resistivity of about 2*10 12 ohm cm. The current and the average charge signal are reported for three different HgI 2 pixel detectors. The signal for one of the detectors is about 1100 electrons at 800 V bias voltage and for the second detector, the resistivity is in the same order of magnitude and the charge collection is somewhat better, reaching 1600 electrons at 700 V. One of the detectors was connected to a second hybrid designed for mounting of 8 castor 1.0 chips. CASTOR 1.0 is a VLSI circuit designed for imaging and the results are being evaluated.

Preparation of polycrystalline mercuric iodide very thin (1 μm) films using laser ablation and thick films (100–600μm), using hot pressing, hot wall vapor deposition and screen printing methods, fabricated as radiation detector plates are briefly described. X-ray diffraction, photoluminescence and optical microscopic measurements as well as response to nuclear radiation will be given. Finally, recent results obtained with a large area imaging pixel detector will be shown.

During the beam test of a tracker prototype for the Compact Muon Solenoid detector proposed for the LHC, the time response of the Microstrip Gas Chambers was studied using different gases and chamber gaps. The subsequent efficiency to identify the bunch crossing at LHC is discussed for several algorithms used in the off-line signal processing of the data.

A prototype of the barrel Tracking Detector of the Compact Muon Solenoid (CMS) experiment proposed for LHC was built and tested in a beam and in a magnetic field of up to 3 T. It contained six microstrip gas chambers, 25 cm long, and three double-sided silicon microstrip detectors, 12.5 cm long. We report some preliminary results on the performance of the chambers.

The need to understand surface and space charging of microstrip gas chambers requires a study of transverse diffusion for inhomogeneous electric fields. A differential equation is deduced for the time dependence of the root-mean-square dispersion of the distribution of drifting charges. Its solution yields estimates of electron clouds approaching the anodes, and of ion clouds leaving them. Comparisons to measurements are presented.

Gas gain variations as functions of time have been observed with microstrip gas chambers. They are attributed here to charging of the substrate surface between electrodes. Based upon the concept of quasi-electrostatic fields a rule of charge accumulation is derived. Gas conductance is studied in order to apply the rule to a surface exposed to gas. A relation between substrate resistivity and the rate of detected particles for stable gain operation is then obtained by means of this rule. A comparison with experimental results yields good agreement.

Author(s): Andersen, E.; Barnes, P.D.; Blaes, R.; Braun, H.; Brom, J.M.; Cherney, M.D.; Cohler, M.; Cruz, B. de la; Diebold, G.E.; Dunin, B.; Escobales, B.; Fang, R.; Fernandez, C.; Franklin, G.; Garabatos, C.; Garzon, J.A.; Geist, W.M.; Gomez, A.; Greiner, D.E.; Gruhn, C.; Hafidouni, M.; Hrubec, J.; Lacquot, J.L.; Jegham, E.; Jones, P.G.; Kuipers, J.P.; Ladren, M.; Guevara, P. Ladron de; Liko, D.; Lopez-Ponte, S.; Govhoiden, G.; MacNaughton, J.; Michalon, A.; Michalon-Mentzer, M.E.; Mosquera, J.; Natkaniec, Z.; Nelson, J.M.; Neuhofer, G.; Ogle, W.; Heros, C. Perez de los; Plo, M.; Porth, P.; Powell, B.; Quinn, B.; Ramil, A.; Riester, J.L.; Rohringer, H.; Sakrejda, I.; Thorsteinsen, T.; Traxler, J.; Voltolini, C.; Yanez, A.; Ye, Y.; Zybert, R.

Results are presented on the exclusive charged current antineutrino production of one pion using the data of the Gargamelle propane experiment at CERN PS. The isospin structure of the charged weak current is studied as well as the energy dependence of the total cross section for π − antineutrino production, which is compared with the prediction of the Adler model.

Angular correlations between two pions in the 5-pion final states are studied. A comparison between neutral, like-charged and unlike-charged pion-pion system is done. Evidence is shown for a strong π 0 π 0 correlation in the asymmetry parameters as well as in the mass distribution. This effect is interpreted in terms of the scattering length approximation.

Interactions of 10 GeV/ c K + incident on nuclei producing the K + π + π − system have been analysed by the longitudinal phase-space technique, which improves the selection of coherent events and allows a suitable analysis of the K + π + π − mass spectrum. Taking into account the experimental resulution and form factor effects, and comparing the data with results on protons (hydrogen bubble chamber data), it appears that the low-mass region of the spectrum is favoured by coherent production. Spin-parity analysis of the Q + confirms the 1 + value.

The design of a TPC for a high-multiplicity environment is described. The sense plane is composed of a matrix with 40 rows of short anode wires. The end-cap is completed with rod and wire electrodes to establish the amplification region and to minimize space charge effects. The digital readout of more than 6000 channels is performed by a combination of purpose-built comparators and FASTBUS TDCs. The performance of the chamber is briefly described, and some ideas to improve the hit efficiency and resolution in a new end-cap design are discussed. © 1989.

On a selected sample of 2171 events, observed in the big heavy liquid bubble chamber Gargamelle at CERN, the charged current total cross section for antineutrino on nucleons has been determined up to the laboratory energy E v = 8 GeV . The total cross section is found to be a linear function of the antineutrino energy expressed by σ tot (E v ) = (0.26 ± 0.020) × 10 −38 × E v ( GeV ) cm 2 . The energy dependence of 〈q 2 〉 v is found to be given by 〈q 2 〉 v = (0.15 ± 0.04)E v + (0.05 ± 0.12) ( GeV /c) 2 . With a simplified nuclear model the ratio of cross sections on neutrons andprotons has been estimated as a function of energy and for two different values of the scaling variable x . The results are compared with the prediction of the naive quark parton model.

We have studied neutral strange particle production in the bubble chamber Gargamelle filled with propane and exposed to antineutrinos from the CERN PS. Cross sections are presented for Λ, Σ0 and K0 production. Associated production reactions (ΔS = 0) have been observed in the charged and the neutral current channels. From 45 candidates for the quasi-elastic reaction ν p → μ + Λ , on bound and free protons, estimates of the axial transition form factor MA have been made using the total cross section and the t distribution. The weighted average from the two methods is MA = 862 ± 190 MeV. From a subsample of 15 candidates for ν interactions on free protons in propane, with (28±6)% background from ν interactions on bound protons, we obtain MA = 883 ± 243 MeV. The polarization of the Λ hyperons has been studied for the quasi-elastic reaction. We observe a significant Λ polarization in the production plane, normal to the Λ line of flight. The observed polarizations agree well with the predicted theoretical polarizations without any contribution from second-class axial coupling.