Use Of Photomultipliers Research Articles

Density Fluctuations Measurement by Rayleigh Scattering Using a Single Photomultiplier

Rayleigh scattering provides a direct nonintrusive method for density measurement, which is of particular interest in aeroacoustics. However, two major concerns arise linked to the use of photomultipliers. First, the detection of photon flux is corrupted by the presence of dust particles in the flow. An original signal processing is proposed in this study to remove their signatures. Second, the random arrival of photons on a photomultiplier induces shot noise, which can be partly removed by using two photomultipliers. It is shown in this study that a single photomultiplier combined with suitable processing can also be used to remove shot noise. Both approaches are compared for the case of a compressible subsonic jet exhausting in an anechoic wind tunnel.

Experimental investigation of silicon photomultipliers as compact light readout systems for gamma-ray spectroscopy applications in fusion plasmas.

A matrix of Silicon Photo Multipliers has been developed for light readout from a large area 1 in. × 1 in. LaBr3 crystal. The system has been characterized in the laboratory and its performance compared to that of a conventional photo multiplier tube. A pulse duration of 100 ns was achieved, which opens up to spectroscopy applications at high counting rates. The energy resolution measured using radioactive sources extrapolates to 3%-4% in the energy range Eγ = 3-5 MeV, enabling gamma-ray spectroscopy measurements at good energy resolution. The results reported here are of relevance in view of the development of compact gamma-ray detectors with spectroscopy capabilities, such as an enhanced gamma-ray camera for high power fusion plasmas, where the use of photomultiplier is impeded by space limitation and sensitivity to magnetic fields.

Study of electron avalanche multiplication in gaseous argon detectors at low pressure and operating at cryogenic temperature

We are developing a photodetector sensitive to liquid noble gas scintillation light which is able to operate down to liquid nitrogen temperature (77 K). It has to be a simple, cheap and compact device, with a photocathode surface comparable to that of photomultipliers and it has to be able to produce fast signals for timing and triggering purposes. We studied the possibility of coupling a standard photocathode to a suitable electron multiplication system in gas; this would offer a cheap alternative to the use of photomultipliers. Gas avalanche multiplication at cryogenic temperatures and low pressure was observed in a small prototype chamber. Gains of the order of 10 3 were obtained in pure argon, while gains up to 10 5 were achieved using argon/methane mixture in cryogenic environment.

A multi channel dosimeter based on scintillating fibers for medical applications

Dosimetry with plastic scintillators is an interesting alternative for the measurement of the absorbed dose. A scintillator does barely disturb the radiation field due to its mass absorption coefficients which is water-equivalent in a wide range of energies. Furthermore, plastic scintillation dosimeters provide a fast and direct reading of the measured value combined with a high-spatial resolution. In the set-up described so far, the light produced by the scintillators was transported via light-guides to single-channel or multi-channel photomultipliers to be transformed into an electric current read out by pico-amperemeters. The use of photomultipliers becomes expensive and complicated for a dosimeter system with many parallel channels. For such applications, an image intensifier coupled to a CCD is a simpler approach which can read out some 80 fibers in parallel [M. Garg, Konzeption, Aufbau and Test eines Vielkanal-Dosimeters mit szintillierenden Fasern, WUB–DIS 96–17, Universität Wuppertal, 1996 and I.M. Gregor, Ein Vielkanaldosimeter mit szintillierenden Fasern–Klinische Messungen bei Energien oberhalb 1MeV, WU D 98–14, Universität Wuppertal, 1998]. In this note, the design and the first successful measurements of a prototype set-up are described.

Ignition of spurting hydrogen jets behind a reflected shock wave.

This paper describes an experimental study of the ignition of unsteady hydrogen jets injected into compressed high temperature air behind reflected shock waves. Hydrogen gas was injected into the test section 8.511. ms before incident shock wave was reflected from the end plate. Pressure measurements as well as the detection of light emission due to combustion of a hydrogen-oxygen gas mixture were made by the use of photomultiplier and pressure gages. We found : (1) The ignition delay times observed under the temperature ranging between 800 to 1600 K were from 0.5 to 15 ms ; (2) There exist ignition limits similar to the results of the experiments with premixed gases. However we did not find any clear "explosion-peninsula" ; (3) The Ignition delay time of unsteady hydrogen jets compressed by means of a shock tube was longer than the premixed one, because the hydrogen jets need some time to mix with air ; (4) When much hydrogen which was cooled by adiabatic expansion spurted into the low density test density test section, it caused the temperature of the air in the test section to fall, and the ignition delay time to become long.

A liquid scintillation detector module for use in bulk-sample and whole-body counters

The construction and properties of a rectangular liquid scintillation detector module are described. The module is designed for simplicity of construction, optimum light collection and economic use of photomultipliers. The advantages of the design are considered in relation to the use of the module in large sensitive counters.

Electrophysiological studies of the protozoan, Stentor coeruleus.

AbstractTransmembrane potentials and membrane characteristics of Stentor coeruleus were studied by means of microelectrodes and standard electrophysiological techniques. Intracellular resting potentials were found to be variable and recordable for only a brief span of time owing to the encapsulation of the recording electrodes. During this brief time span of recorded resting potentials were anamolous in that they were generally of positive polarity.When an extended Stentor was stimulated to contract, a 10–60 mv negative‐going transient response was recorded from intracellular electrodes. After the electrodes had been encapsulated, a diphasic transient response was observed when the penetrated animal contracted. Simultaneous recordings from intracellular and encapsulated electrodes showed that the diphasic and negative‐going transient responses occurred simultaneously.Contractions of Stentor occurred in 7 to 8 msec following a 2 to 3 msec latent period after a suprathreshold shock. Records obtained by use of photomultiplier and microelectrodes indicated that the contractions began 1.8 msec after the onset of the diphasic response.Prepotentials were observed prior to mechanically stimulated responses.

Amplifier and pulse-counter for fast, low level photometry

A logarithmic amplifier and a pulse-counting amplifier are described, and some notes given on the practical use of photomultipliers to measure light fluxes in the range 10-12 to 10-6 lumen whilst maintaining a response from d.c. to 3 kc/s.

Photomultiplier Counters in High-Energy Physics Experiments

Techniques in the use of photomultipliers in high-energy nuclear physics are presented by the description of experiments that have been prominent recently. The applications involve the use of photomultipliers with attendant amplification at the limit of present possibilities of time resolution. Such applications include measurements of time of flight, measurement of lifetime of heavy unstable particles, and the elimination of background effects in the pulsed radiation fields of high-energy accelerators. The need for the development of large fast-rising signals from events of small light output, such as Cerenkov light pulses, is made apparent, and a discussion of the performance desired from electron multipliers in view of contemplated experiments is presented.

Utilisation des grillages en spectrophotométrie hétérochromatique; méthode d'extradéfocalisation

The use of photomultipliers has given the possibility of accurate measurements of luminous fluxes of low intensity. The recommended methods for reducing light intensities in a given way are now susceptible of rigid and thorough control. Several methods have been compared in this way and the working conditions of the most promising one, the method of rotating gauzes (grillages tournants) have been investigated. Under normal conditions the grids do not show an optically neutral behaviour: diffraction phenomena causing a reduction of the light generally increasing with increasing wave-length. Working conditions to eliminate this inconvenience in using the gauzes could be found.

Detection and Recording of Optical Transients by Photo-multipliers

THE use of photo-multipliers for the detection and recording of optical transients is well known in the fields of gaseous discharge and of scintillation counting. In both these fields, involving time-intervals short compared with a microsecond, the limit of detection of the system is set by the shot noise associated with the photo-current and not by the thermionic emission from the cathode. The thermionic emission from the cathode of a photo-multiplier is usually quoted as about 10−15 amp./cm.2 or approximately 10−14 amp. for the whole cathode. This corresponds to an average rate of emission of electrons of approximately one electron in ten microseconds, and the probability of emission of an electron during any interval of time short compared with a microsecond is small.