D. Piedigrossi

A new position-sensitive photon detector based on an imaging silicon pixel array (ISPA-tube)

Abstract A new position-sensitive photon detector has been developed and operated for the first time. It consists of a photocathode, evaporated on an optical fibre window, confronted at 30 mm distance by a silicon chip containing 1024 pixels of 75 μm × 500 μm edges and bump-bonded to their individual readout electronics. This ISPA-tube is particularly suited for particle tracking with scintillating fibres (particle- and nuclear physics, medicine, biology, etc.) and for position-sensitive photon counting from low intensity light sources (astronomy, etc.). Examples for both kinds of application are displayed.

Further results on photoelectron counting with small diameter scintillating fibres

Abstract We measured the number of photoelectrons released from the photocathode of a newly available hybrid photomultiplier tube (HPMT) by photons from scintillating fibres. About 1600 individual 60 μm diameter fibres are contained in fused square bundles of 2.5 mm edges. The number of photoelectrons per mm fibre path changes from 10.6 at zero to 1 at 2 m bundle length. The potential difference between the HPMT photocathode and its electron detecting silicon diode amounted to 13 kV.

Development of precision Time-Of-Flight electronics for LHCb TORCH

The TORCH detector is proposed for the low-momentum particle identification upgrade of the LHCb experiment. It combines Time-Of-Flight and Cherenkov techniques to achieve positive π/K/p separation up to 10 GeV/c. This requires a timing resolution of 70 ps for single photons. This paper reports on the electronics developed for such measurements, using commercial Micro Channel Plate (MCP) devices and custom ASICs (NINO and HPTDC). The intrinsic timing resolution of the electronics measured with electrical test pulses is 40 ps. With the MCP photon detector and a pulsed laser, a resolution of 90 ps has been recorded in laboratory tests and 130 ps in test beams.

An ISPA-camera for gamma rays with improved energy resolution

An Imaging Silicon Pixel Array (ISPA)-tube with nonfiber optic quartz window has been tested with respect to spatial and energy resolutions. The 122-keV /spl gamma/-quanta of a Co/sup 57/ source was converted in a planar YAP-disc or in optically separated YAP-pillars of 0.6/spl times/0.6-mm/sup 2/ or 0.3/spl times/0.3-mm/sup 2/ cross sections. The achieved intrinsic spatial resolution is worsened when compared to the ISPA-version with fiber optic glass window but is still in the submillimeter region. As the YAP emission spectrum is fully covered by the spectral transmission of the quartz window and well adapted to the photocathode quantum efficiency spectrum, the resulting improved energy resolution allows for triggering of ISPA-events within a selected energy window at the 122-keV total absorption peak. This mode of operation, since it strongly reduces the number of unwanted events, is essential for the application of a /spl gamma/ camera in environmental conditions where a wider energy range from other background sources may be present.

A HPMT BASED SET-UP TO CHARACTERIZE SCINTILLATING CRYSTALS

Abstract We have developed a fully automatic measurement set-up, capable of measuring light yields arising from scintillating crystals in a linear range of about four orders of magnitude. The photodetector is a hybrid photomultiplier tube specially developed to optimize linear range and photon detection. Crystal and photodetector are temperature controlled by a closed water circuit, as this is essential when measuring low light yield scintillating crystals with a marked temperature dependence of their light yield. Gamma sources can be placed either on top or on the side of the crystal. In this latter case, the source can be automatically moved by a computer-controlled step motor to provide a uniformity profile of the light yield along the crystal. Tagged and not-tagged operation modes are possible. The whole set-up is computer-controlled in an effort to provide fast and reliable measurements, to characterize many crystals per day. This is important for the quality control of the lead tungstate crystals that will be applied in the electromagnetic calorimeter of the CMS-detector at the LHC at CERN.

First beam exposures of a scintillating fibre tracker read out by an ISPA-tube☆

Abstract The ISPA (imaging silicon pixel array)-tube is a new position-sensitive photon detector. It represents a vacuum-sealed cylinder of 45 mm length and 35 mm diameter, which encloses a photocathode confronted at 30 mm distance by a silicon chip containing 1024 pixels of 75 μ m × 500 μ m edges bump bonded to their individual front-end electronics. The photoelectrons were accelerated by 20 kV potential difference towards this anode chip. Track patterns, emitted from a fibre tracker (composed of 60 μm diameter scintillating fibres) and exposed to 120 GeV/ c negative pions, were read out with this recently developed device. The Gaussian of the track residuals indicates 42 μm standard deviation σ. The centre-of-gravity precision ϵ=σ/ N ( N = number of hits) amounts to 15 μm and the angular precision of the tracks peaks at 8 mrad.

Performance of a hybrid photon detector prototype with electrostatic cross-focussing and integrated silicon pixel readout for Cherenkov ring detection

Abstract We report on the first test beam performance of a hybrid photon detector prototype, using binary readout electronics, intended for use in the ring imaging Cherenkov detectors of the LHCb experiment at the CERN Large Hadron Collider. The photon detector is based on a cross-focussed image intensifier tube geometry. The anode consists of a silicon pixel array bump-bonded to a binary readout chip with matching pixel electronics. The detector has been installed in a quarter-scale prototype vessel of the LHCb ring imaging Cherenkov system. Focussed ring images produced by 120 GeV/c negative pions traversing an air radiator have been recorded. The observed light yield and Cherenkov angle resolution are discussed.

The TORCH PMT: a close packing, multi-anode, long life MCP-PMT for Cherenkov applications

Photek (U.K.) and the TORCH collaboration are undertaking a three year development program to produce a novel square MCP-PMT for single photon detection. The TORCH detector aims to provide particle identification in the 2-10 GeV/c momentum range, using a Time-of-Flight method based on Cherenkov light. It is a stand-alone RD project with possible application in LHCb, and has been proposed for the LHCb Upgrade. The Microchannel Plate (MCP) detector will provide a single photon timing accuracy of 40 ps, and its development will include the following properties: (i) Long lifetime up to at least 5 C/cm(2); (ii) Multi-anode output with a spatial resolution of 6mm and 0.4mm respectively in the horizontal and vertical directions, incorporating a novel charge-sharing technique; (iii) Close packing on two opposing sides with an active area fill factor of 88% in the horizontal direction. Results from simulations modelling the MCP detector performance factoring in the pulse height variation from the detector, NINO threshold levels and potential charge sharing techniques that enhance the position resolution beyond the physical pitch of the pixel layout will be discussed. Also, a novel method of coupling the MCP-PMT output pads using Anisotropic Conductive Film (ACF) will be described. This minimises parasitic input capacitance by allowing very close proximity between the frontend electronics and the MCP detector.

Gamma spectroscopy and optoelectronic imaging with hybrid photon detector

Abstract Hybrid Photon Detectors (HPD) detect light via photocathodes and accelerate the emitted photoelectrons by an electric field towards silicon PIN-anodes, where they are absorbed and generate electronic signals. We have developed two specific types of HPDs: (1) Hybrid photomultiplier tubes for photon counting and gamma spectroscopy; (2) Imaging silicon pixel array tubes for optoelectronic cameras. This paper will illustrate the main achievements, which we obtained in the last years, and will describe and discuss our present main RD 29.40; 29.30; 87.59

The ISPA-tube and the HPMT, two examples of a new class of photodetectors: the hybrid photo detectors

A new class of photodetectors, the Hybrid Photo Detectors (HPD), is coming up as a major breakthrough in photodetection. The principle of the HPD is to couple a fully depleted silicon diode or silicon diode array to a photocathode in a vacuum tube. At present HPDs with one diode or a few diodes (Hybrid Photo Multiplier Tubes, HPMT) are commercially available (DEP, The Netherlands, and Hamamatsu, Japan) and a position sensitive photon detector (the Imaging Silicon Pixel Array tube, ISPA tube) is under development in our group (in collaboration with the RD-19 collaboration at CERN). We shall present the main features of HPDs and then our main results and applications for both HPMTs and ISPA tubes on photon counting, on imaging and on high energy physics applications.