Showing papers on "Photomultiplier published in 1974"

Experimental distinction between the quantum and classical field-theoretic predictions for the photoelectric effect

Abstract: We have measured various coincidence rates between four photomultiplier tubes viewing cascade photons on opposite sides of dielectric beam splitters. This experimental configuration, we show, is sensitive to differences between the classical and quantum field-theoretic predictions for the photoelectric effect. The results, to a high degree of statistical accuracy, contradict the predictions by any classical or semiclassical theory in which the probability of photoemission is proportional to the classical intensity.

Measurement of absorption and noise in an x‐ray image intensifier

Abstract: Three experimental methods for measuring the noise‐equivalent absorption of an x‐ray image intensifier are described. In all cases, the image intensifier is irradiated with a source of x rays or γ rays, and the output is monitored with a photomultiplier. In one method the rms value of the photomultiplier current is observed as a function of the bandwidth of the measuring circuit. In the second method, the scintillation pulse spectrum is recorded, and its moments computed to give the required information. In the third method, the response to a series of short bursts of radiation is measured. The noise‐equivalent absorption is determined from the standard deviation of a large number of observations, automatically recorded. The three methods are described and compared, and typical results are shown.

A Measuring System for Studying the Time-Resolution Capabilities of Fast Photomultipliers

Abstract: A measuring system has been developed for studying and optimizing the time-resolution capabilities of fast photoelectric devices, such as standard and microchannel type photomultipliers. The system incorporates a subnanosecond light-pulse generator capable of operating at repetition frequencies up to 3 MHz with output light pulses having a full width at half-maximum of less than 200 psec, and a zero-crossing discriminator which has a time walk of ±40 psec over a 170 mV to 8 V input-pulse amplitude variation. Averaging the data from several successive measurements, the measuring system time resolution is 20 psec.

High efficiency scintillation detectors

Abstract: A scintillation counter consists of a scintillation detector, usually a crystal scintillator optically coupled to a photomultiplier tube which converts photons to electrical pulses. The photomultiplier pulses are measured to provide information on impinging radiation. In inorganic crystal scintillation detectors to achieve maximum density, optical transparency and uniform activation, it has been necessary heretofore to prepare the scintillator as a single crystal. Crystal pieces fail to give a single composite response. Means are provided herein for obtaining such a response with crystal pieces, such means comprising the combination of crystal pieces and liquid or solid organic scintillator matrices having a cyclic molecular structure favorable to fluorescence.

Circuit device for secondary electron multipliers

Abstract: A circuit device for electron multipliers, especially photomultiplier tub in which the amplification is varied by switching the number of active dynodes. Sensitivity ranges from diode-mode up to a multiplier with full number of dynodes. The signal is taken from the last active dynode, and from the cathode in diode-mode. Any switchable dynode is provided with its own load resistor inserted between the relevant dynode and a dynode voltage divider. An amplifier connected to the last active dynode and to the dynode voltage divider provides a feedback that compensates for voltage drops at the next lower dynodes due to the finite impedance of the dynode voltage divider. The circuit device features fast signal risetime, high linearity and wide dynamic signal range together with high DC-current capability and clean transient response. Applications are transient-spectrophotometers where high signal-to-noise ratios are needed, accurate pulse-height-analysis, etc. The device may be constructed as a self-contained unit.

1. Photomultipliers: Their Cause and Cure†

Abstract: Publisher Summary This chapter describes the basic physics and construction of photomultipliers. Photoelectric photometry is a fundamental technique in observational astronomy. The photo emissive detector produces a current supposedly proportional to the light intensity falling on it, thus reducing photometry to a simple electrical measurement that can be made very accurately. A thick, internal cold-box window can be helpful in lowering cathode temperature, but it increases cosmic-ray noise and so it may not reduce the total dark noise. A lower string current reduces the heat dissipated in the string, and hence the heat input and thermal gradients at the tube base. Nonlinearity can vary with the position of the illuminated spot on the cathode, and with wavelength. It is suggested that the area of the photocathode illuminated during measurements, and the wavelength of the radiation, are the same as those used during calibration. The pulse-height distribution due to thermionic or field emission from the cathode is similar to that caused by photoelectrons.

Scintillation camera with improved linearity

Abstract: An Anger-type scintillation camera having analog circuitry in the form of seven correction generators each associated with one of a central seven of an array of nineteen photomultiplier tubes to compensate for spatial non-linearities in the camera. Each correction generator is active for scintillations produced by gamma ray interactions near its associated photomultiplier tube and produces correction signals which are added to the coordinate signals of an Anger-type camera to produce corrected corrdinate signals which represent more accurately the true spatial coordinates of the gamma ray interaction.

Reducing Gain Shifts in Photomultiplier Tubes

Abstract: Gain shifts in photomultipliers from count-rate changes can be minimized by using only five active stages, making up the gain with a low-noise preamplifier. Further reductions sometimes result from a dim light shining on the dynode structure. Reductions to less than 1 part in 600 were seen.

An inexpensive nanosecond light pulser for use in photomultiplier system testing

Abstract: A nanosecond light pulser of modest cost is described, which is suitable for use in the testing of large photomultiplier systems, where each phototube requires an individual pulser. Timing stability (of 200 psec) and light pulse amplitude stability (of 4% from 10° to 40°C) are adequate for all but the most demanding applications. Yellow light emitting diodes are used to obtain satisfactory matching to photomultipliers with S‐11 response curves.

Photomultiplier circuit including means for rapidly reducing the sensitivity thereof

Abstract: A simple, reliable and inexpensive control circuit is described for rapidly reducing the bias voltage across one or more of the dynode stages of a photomultiplier, to substantially decrease its sensitivity to incoming light at those times where excess light intensity might damage the tube. The control circuit comprises a switching device, such as a silicon controlled rectifier (SCR), coupled between a pair of the electrodes in the tube, preferably the cathode and first dynode, or the first and second dynodes, the switching device operating in response to a trigger pulse applied to its gate to short circuit the two electrodes. To insure the desired reduction in sensitivity, two switching stages, the devices be employed between two of the electrode stages, the devices being operated simultaneously to short circuit both stages.

Signal induced noise in a 56 TUVP photomultiplier

Abstract: Experiments are reported that show that incident irradiances as low as 014 pW cm-2 and lasting only a few tens of microseconds produce a significant enhancement in the dark noise of a 56TUVP photomultiplier in the few hundreds of microseconds following the removal of the signal from the cathode The induced noise is shown to be proportional to the signal strength and to decay as the inverse square of the time following the end of the signal The result of this effect on a time gated measurement of a signal of known amplitude is briefly considered

Radiation detector system using an inorganic scintillator crystal detector with an optical filter for aerial dosemetry

Abstract: A radiation detector system used in aerial dosimetry in which an inorganic scintillation crystal detector and spectral filter are coupled to a photomultiplier tube and the requisite electronic circuits. The crystal detector is pointed toward an area to be monitored for X-ray or gamma ray and the resulting optical radiation therefrom is applied to the photomultiplier tube for converting to an electrical output therefrom which is monitored to indicate the radiation dosage.

Circuit for light measuring devices and method

Abstract: Circuit and method of use thereof in light measuring devices and, particularly, devices for measuring optical density and the calibration of neutral density filters. The basic circuit includes a phase-inverting operational amplifier with a first current determining means connected to one input of the amplifier and a second current determining means including a photomultiplier tube connected between the output of the amplifier and the one input as a feedback circuit. Optical density measurements are made by directing a constant light level to the photomultiplier tube. A variable circuit parameter(s) in one of the two current determining means is used to keep the cathode voltage of the photomultiplier at the same level for two conditions, i.e., when a specimen is in the light path and when the specimen is not in the light path. The magnitudes of such circuit parameter(s) for the two conditions are used to calculate the optical density of the specimen.

Photomultiplier tube having impact ionization diode collector

Abstract: A photomultiplier tube (PMT) converts a received light signal to an output electrical signal of substantially greater intensity by employing a photocathode to convert incident light to free electrons, a plural dynode accelerating structure for effectively multiplying said free electrons, and an impact ionization diode (IID) for further multiplying and collecting said free electrons to provide a corresponding electrical output signal. The PMT can be an electrostatic device, in which the photocathode and the dynodes are mounted in opposed staggered positions, or a static crossed field device, in which the photocathode and the dynodes all are mounted opposite an accelerating rail and a magnetic field is provided to urge the electrons laterally along the tube. The IID''s junction is reverse biased and the entire diode is maintained at a substantially higher potential than the last dynode. The PMT can be gain controlled or turned off without affecting dynode potentials by controlling the IID''s potential. Due to the gain provided by the IID, dynode current can be reduced greatly, thereby to increase substantially the tube''s life without affecting its overall gain.

Double-Beam Two-Channel Wavelength-Modulated Reflectometer

Abstract: A double-beam wavelength-modulated reflectometer utilizing a single detector and without a reflectivity reference has been described. Separate electronic channels are used for the two wavelengths at which the reflectometer alternatively operates. The gain of one of the channels is controlled by feedback to eliminate the instrumental background. The derivative and conventional reflectivity are measured simultaneously. The influence of the photomultiplier dark current and scattered light on the accuracy and of some design parameters on the SNR have been evaluated. The system has been checked by measuring the derivative and conventional reflectivity spectrum of GaAs.

An accurate method of photomultiplier gain determination

Abstract: The unique features of pulse counting coupled with anodic current measurement by an electrometer are used to determine photomultiplier gain accurately under actual experimental conditions.

Photomultiplier gate with gating times larger than a few microseconds

Abstract: A photomultiplier gate based on pulsing the first dynode with two transistor switches in series‐shunt connection is described. It provides a high cutoff efficiency with moderate switching speeds and has the advantage of simplicity and versatility.

Energy compensated spectrofluorometer

Abstract: An energy-compensated spectrofluorometer of the time-shared double beam type employing a rotating chopper mirror disc providing a main measure channel as one of the time-shared outputs of a photomultiplier tube and a compensating reference channel generated by a reference light whose output is conveyed by a light pipe to the cathode of the photomultiplier tube, generating the other time-shared output thereof. The energy correction is derived from a thermal detector cell receiving part of the excitation beam, and the reciprocal of the thermal detector cell signal is subtracted from the dark currentcorrected reference channel signal and is employed to adjust the high voltage supplied to the photomultiplier tube, thereby adjusting its gain. The measure channel includes means to compensate the measure signal for non-uniform spectral sensitivity of the photomultiplier tube, as well as for dark current. The reference channel signal is also modified to compensate for wavelength-dependent variations of quantum intensity in the excitation beam.

Photomultiplier Selection Criteria for Satellite Experiments

Abstract: Forty-six RCA C 7151 Q photomultiplier tubes and thirty-five EMI 9711 NB photomultiplier tubes have been tested for use in the telescope of the COS-B gamma-ray experiment. The tubes were selected taking into account gain, linearity, fatigue behaviour and temperature characteristics. Besides identifying the most suitable tubes for this application, the experimentally determined values make it possible to derive "typical" behaviour parameters which can be used to pre-select tubes at the ordering stage. The results obtained with the EMI tubes clearly demonstrate a striking difference between "typical" catalogue values and "typical" measured values for the batch tested.

Electronic Signal Processing for Raman Scattering Measurements

Abstract: General signal processing techniques for laboratory Raman spectroscopy and Remote Raman spectroscopy using cw and pulsed lasers are discussed. Chopped and pulsed source/time gated detection techniques are outlined. Detectors such as photomultiplier and image tubes, SEC Vidicon sensors, image dissectors, and multiplex spectrometers are discussed and some of their relative merits evaluated. Computer aided data reduction and techniques for fluorescence suppression in the signal and in the display are covered.

Sample positioning apparatus

Abstract: Apparatus for use in alpha particle counting with such as photomultiplier tubes, comprising a platform and linkage mechanism whereby samples are moved in linear manner toward and away from ends of the photomultiplier tubes.

Simple device for photomultiplier cooling.

Abstract: As known, suitable cooling of photoemissive surfaces is necessary in order to reduce the dark current produced by thermoionic emission. The required operating temperature for the different photocathode materials is generally around -40 °C but in other cases, as for example AgOCs photocathode, this limit extends down to –160 °C. Many devices have been described for this purpose. Some of these use more or less tight thermal contact, to cool the photoemissive surfacebetween the glass envelope of the photomultiplier and a freezing liquid container. Some problems arise from the necessary electrical insulation between the glass and the metallic envelope if the cathode has to be connected at the negative voltage supply, as commonly happens. Moreover the temperature uniformity is poor. Another class of more reliable photomultiplier coolers is based on the circulation of low temperature dry gas. The drawback which is common to these applications is the use of sealed envelopes containing the photomultiplier held at low temperature including the divider often potted together with the photomultiplier itself. We have constructed a circulation cooler suitable to reach – 165 °C in which cited limitations are avoided. Figure 1 shows the used device. The inner envelope (shaded region) is made of polyethylene foam, the external one is a metallic housing. The device contains only a part of the photomultiplier, including the photocathode sensitive zone. The rear part of the photomultiplier and the associated networks are at room temperature. The radiation reaches the photocathode traversing two windows of suitable transmitting material, which are the bases of a cylindrical can. A and B tubes are connected to this can. The circulating dry gas at room temperature (tubes A, B) prevents fogging of the external window and after passing in the dewar vessel is sent through tube C to cool the photomultiplier and finally flows out through tube D.

Electron beam fluorescence system to measure gas density in impulse facilities

Abstract: Very rapid measurements, ranging from a few microsecond to milliseconds in duration, characterize studies made in shock regions or behind them. A system to measure gas density under such conditions in a 15.24-cm (6-in.) expansion tube is described. The basic elements are an electron beam of moderate energy and high current capability, an optical detector, and the associated electronics and data readout equipment. A heated-cathode electron gun, capable of pulsed operation and delivering up to 200 milliamperes current, provides the source of electrons. Optics include a simple collector lens, aperture, collimator lens, filters, and a photomultiplier tube. The photomultiplier output signal was recorded by means of photographed oscilloscope traces for pulsed beam operation.

Measurement of an overload effect in a photomultiplier (occurring in atmospheric lidar studies)

Abstract: Measurements are described in which a photomultiplier tube has been subjected to a short very intense pulse of light. This results in a temporary enhancement of the dark current in the photomultiplier, lasting for at least 500 mu s. The effect is particularly important in studies of the atmosphere using laser radar techniques when this condition is often encountered.

Photon Counting with Fiber-Optic Coupled Scintillators

Abstract: By coupling a scintillation crystal to a photomultiplier with fiber optics, one can place the detector in areas not normally accessible to a crystal-photomultiplier combination. Although fiber optics provide a flexible optical coupling, serious light losses cause about a factor of 10 reduction in the light intensity reaching the photomultiplier. Most of the light loss is due to the small acceptance angle of the fiber optics with transmission losses and crystal aperture losses playing secondary roles. Attention to the design and to the selection of the crystals and fiber optics help to optimize the light collection efficiency. The light losses lower the scintillation intensity from low-energy (10 to 40 keV) radiation into the region where photomultiplier noise becomes important (3.5 - 18 photoelectron equivalents). This noise consists of Cerenkov events, faceplate scintillations, electroluminescence, afterpulses and thermionic emissions. For effective low background counting this noise must be reduced. A combination of pulse-shape discrimination, magnetically limiting the photocathode area and shielding were effective in reducing the background rate from 513±3 counts/minute to 10.0±0.5 counts/minute in the energy range from 6.5 to 40 keV. By coincidence counting, in the same energy region, a background rate of 1.60±0.28 counts/minute was obtained.