Ultraviolet Cherenkov Research Articles

Readout chain validation of INFN modules for the CTA-pSCT camera

Abstract The Italian Institute of Nuclear Physics (INFN) is currently involved in the R&D for the integration of Fondazione Bruno Kessler (FBK) Silicon Photomultipliers (SiPM) in the focal plane camera for the prototype of the Schwarzschild–Couder Telescope (pSCT) proposed to integrate the Cherenkov Telescope Array (CTA) observatory . High density FBK SiPMs optimized for the detection of Near Ultraviolet Cherenkov light (NUV-HD) will be used to equip the camera, coupled to the TARGET-7 readout electronics. A first production of 9 INFN modules is being tested and will be installed on the focal plane of the pSCT camera. Each module consists of 64 6 mm × 6 mm pixels, based on 40 μ m × 40 μ m microcells, arranged in 16-pixel matrices. The front-end electronics is based on the TARGET-7 ASIC, a 16-channel chip for sampling and digitization of the signal. Here we report measurements of the performances of the complete readout chain, including results regarding homogeneity in terms of gain and signal-to-noise ratio .

Transparency of 0.2% GdCl 3 doped water in a stainless steel test environment

The possibility of neutron and neutrino detection using water Cherenkov detectors doped with gadolinium holds the promise of constructing very large high-efficiency detectors with wide-ranging application in basic science and national security. This study addresses a major concern regarding the feasibility of such detectors: the transparency of the doped water to the ultraviolet Cherenkov light. We report on experiments conducted using a 19-m water transparency measuring instrument and associated material test tank. Sensitive measurements of the transparency of water doped with 0.2% GdCl 3 at 337, 400 and 420 nm were made using this instrument. These measurements indicate that the use of GdCl 3 in stainless steel constructed water Cherenkov detectors is problematic.

A Cherenkov radiator for FEL-synchronized VUV-pulses at a linac-based FEL

A possible way to carry out two-color IR + VUV pump-probe experiments at linac-based FELs is proposed. The idea is to supply an FEL facility with a gas cell filled with helium or hydrogen, so that the electron beam, upon passage through the undulator, could be used to generate ultraviolet Cherenkov radiation. Such a Cherenkov radiator is shown to provide a reasonably high spectral-angular density of photons in a wide range of wavelengths from visible (300–400 nm) down to the VUV (65–70 nm). When averaged over a macropulse, the intensity of such a source exceeds that of synchrotron radiation from a wiggler in a modern storage ring. The spatial quality of the source is inferior to that of synchrotron radiation, but the synchronization to the infrared FEL pulses, which is crucial for most applications, is obviously perfect.

Observation of the Crab Nebula with an ultraviolet Cherenkov camera

Gamma-ray astronomy at energies of a few hundred GeV is now well established, with the observation of emission from the Crab Nebula by at least five independent groups. The technique is based on the detection of the Cherenkov light emitted by gamma-ray induced air showers. It requires clear, moonless nights, which seriously curtail the useful duty cycle. It is shown here that by detecting the UV Cherenkov photons instead of the full visible Cherenkov spectrum, the observations can be extended to moonlit nights, with lower constraints on the background light from the moon and stars, but with a somewhat higher energy threshold.

The Galactic plane: a bench-mark for ultraviolet atmospheric Cherenkov detectors

Abstract The question of the emission of very high and ultra high energy γ rays from the Galactic plane is an experimentally unresolved question. We discuss the detectability of the expected flux in the VHE range by means of ultraviolet Cherenkov telescopes, even with no requirement for hadron-γ discrimination, using a technique alternative to imaging in data analysis. We point out that this kind of measure is probably pertinent for ultraviolet Cherenkov systems, before any measure of discrete sources (the Crab included); this could be then the proper bench-mark for the sensitivity of these systems.

Detection of ultraviolet Cherenkov light from high energy cosmic ray atmospheric showers: a field test

Abstract 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.

Recent results from the DELPHI barrel ring imaging Cherenkov counter

The DELPHI detector installed in the LEP (Large Electron-Positron Collider) is equipped with RICH (ring imaging Cherenkov) counters. The barrel part incorporates a liquid (C/sub 6/F/sub 14/) and a gaseous (C/sub 5/F/sub 12/) radiator, providing particle identification up to 20 GeV/c. The Cherenkov photons of both radiators are detected by TPC (time projection chamber)-like photon detectors. The drift gas (75% CH/sub 4/+25% C/sub 2/H/sub 6/) is doped with TMAE (tetrakis-dimethylamine-ethylene) by which the ultraviolet Cherenkov photons are converted into single free photoelectrons. These are drifted towards multiwire proportional chambers at the end of the drift tubes, and the space coordinates of the conversion point are determined. One half of the barrel RICH is now equipped with drift tubes and has provided results from the liquid radiator since spring 1990. The gas radiator has been tested with C/sub 2/F/sub 6/ as a preliminary filling since August 1990. The data obtained demonstrate the good particle identification potential. For the liquid radiator, the number of detected photons per ring in hadron jets is N=8, whereas for muon pairs (single tracks) N=10 has been obtained. For the gas radiator, 2.1 photons per track were observed, which demonstrates good functioning of the focussing mirrors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Cherenkov viewing device for used-fuel verification

A Cherenkov viewing device (CVD) has been developed to help verify declared inventories of used nuclear fuel stored in water bays. The device detects and amplifies the faint ultraviolet Cherenkov glow from the water surrounding the fuel, producing a real-time visible image on a phosphor screen. Quartz optics, a UV-pass filter and a microchannel-plate image-intensifier tube serve to form the image, which can be photographed or viewed directly through an eyepiece. Normal fuel bay lighting does not interfere with the Cherenkov light image. The CVD has been successfully used to detect anomalous PWR, BWR and CANDU (CANada Deuterium Uranium: registered trademark) fuel assemblies in the presence of normal-burnup assemblies stored in used-fuel bays. The latest version of the CVD, known as Mark IV, is being used by inspectors from the International Atomic Energy Agency for verification of light-water power-reactor fuel. Its design and operation are described, together with plans for further enhancements of the instrumentation.

A photosensitive chamber for cosmic-ray spectroscopy

We present details of the construction and performance of a set of photosensitive chambers intended to detect ultraviolet Cherenkov light in cosmic-ray shower experiments. The particularly simple design of these chambers allows mass production and outdoor operation. Detection efficiency and sensitivity to a few photoelectrons have been measured at the predicted level. Bench test results are shown and performances in true outdoor operation are presented.

A wide dynamic range experiment to measure high energy γ-showers in air by detecting Cherenkov light in the middle ultraviolet

An experiment to study high energy γ rays from localized cosmic sources is described. A number of Al mirrors reflects the Cherenkov light emitted by the showers into photosensitive gas chambers on the mirror focal plane. The use of gas chambers with large active areas allows a sensitivity superior to existing experiments to be reached. Pad readout gives the required angular accuracy. The chamber is sensitive to the middle ultraviolet Cherenkov light produced by the showers in the atmosphere. Since the ozone in the upper atmosphere absorbs the direct ultraviolet light from any outer source, the lower level atmosphere provides a large dark volume in which the Cherenkov radiation from the showers can be isolated.

A water Cherenkov counter sensitive to nonwaveshifted ultraviolet Cherenkov photons

We describe a prototype water Cherenkov counter which has been built and tested with relativistic cosmic ray muons. An analysis of the expected photoelectron yield is described. The predicted result of 315 ± 31 photoelectrons is compared with the experimental result of 272 ± 30 photoelectrons. We find that over 70% of the Cherenkov photons detected have wavelengths less than 400 nm.

The Utah neutrino detector Cherenkov system

Large area directional Cherenkov detectors have been economically constructed at the University of Utah to provide a highly efficient trigger for a hodoscope of sonic ranging cylindrical spark counters. The detectors are water-filled concrete tanks having inside dimensions of 3 ft × 33 ft × 20 ft high, whose two large walls support an array of light collecting elements. A new type of highly efficient light collector which provides a wall coverage of about 70% has been developed and is now in use. Ultraviolet Cherenkov light generated by a relativistic muon passing through a tank is picked up and waveshifted to the visible by the light collectors. The visible light is then viewed by a photomultiplier tube located at one end of each collector. The output from the array on a wall corresponds to ≈ 13 photoelectrons with an average triggering efficiency of about 92%. The angular dependence of the triggering efficiency as well as the technology of operating phototubes underwater is discussed. Four Cherenkov tanks operated in coincidence incorrectly determine the directionality of a passing muon about once in 10 10 transversals.