Photomultiplier Window Research Articles

The time resolution improvement of Cherenkov-Radiator-Window Photomultiplier tube

The improvement of time resolution in time-of-flight positron emission tomography (TOF-PET) relies on the development of scintillation materials and photodetectors. With the introduction of Cherenkov TOF-PET, higher requirements have been placed on the intrinsic timing performance of photodetectors. Our team has proposed a Cherenkov Radiator Window Photomultiplier tube (CRW-FPMT) that uses the Cherenkov radiator directly as the light window, which eliminates the boundary between the scintillator and the photodetector for fast time resolution. This paper mainly discusses the factors influencing its time resolution and optimizes it to achieve a single photon time resolution of 27.2 ps.

An innovative technique for TPB deposition on convex window photomultiplier tubes

Tetraphenyl-butadiene (TPB) is an organic fluorescent chemical compound generally used as wavelength shifter thanks to its extremely high efficiency to convert ultra-violet photons into visible light. A common method to use TPB with detectors sensitive to visible light, such as photomultiplier tubes (PMTs), is to deposit thin layers on the device window. To obtain effective TPB layers, different procedures can be used. In this work a specific evaporation technique adopted to coat 8 in convex windows photomultiplier tubes is presented. It consists in evaporating TPB by means of a Knudsen cell, which allows to strictly control the process, and in a rotating sample support, which guarantees the uniformity of the deposition. Simulation results and experimental tests demonstrate the effectiveness of this evaporation technique from the point of view of deposition uniformity and light conversion efficiency.

Application of direct-injection detector integrated with the multi-pumping flow system to chemiluminescence determination of the total polyphenol index

In this work, we present a novel chemiluminescence (CL) method based on direct-injection detector (DID) integrated with the multi-pumping flow system (MPFS) to chemiluminescence determination of the total polyphenol index. In this flow system, the sample and the reagents are injected directly into the cone-shaped detection cell placed in front of the photomultiplier window. Such construction of the detection chamber allows for fast measurement of the CL signal in stopped-flow conditions immediately after mixing the reagents. The proposed DID-CL-MPFS method is based on the chemiluminescence of nanocolloidal manganese(IV)-hexametaphosphate-ethanol system. The application of ethanol as a sensitizer, eliminated the use of carcinogenic formaldehyde. Under the optimized experimental conditions, the chemiluminescence intensities are proportional to the concentration of gallic acid in the range from 5 to 350 ng mL−1. The DID-CL-MPFS method offers a number of advantages, including low limit of detection (0.80 ng mL−1), high precision (RSD = 3.3%) and high sample throughput (144 samples h−1) as well as low consumption of reagents, energy and low waste generation. The proposed method has been successfully applied to determine the total polyphenol index (expressed as gallic acid equivalent) in a variety of plant-derived food samples (wine, tea, coffee, fruit and vegetable juices, herbs, spices).

Instrumentation of kinetic spectroscopy-21: The use of a compact size photomultiplier tube in kinetic spectroscopy

The use of a compact subminiature size photomultiplier tube in kinetic spectroscopy experiments is explored. Due to the small size, time response is superior to side window photomultiplier tubes normally in use.

Effects of a Color Filter Used in Auriculomedicine on Ultraweak Photon Emission of the Human Body

The human body emits ultraweak photons. It has been demonstrated that feedback regulation of ultraweak photon emission from the hand is detectable utilizing gelatin color filters in complete darkness. Color filters are commonly utilized in auriculomedicine diagnostic procedures based on the radial artery vascular autonomic signal. To evaluate the possibility of an effect by a dark-adapted red filter on (1) local ultraweak human photon emission using different anatomic locations, and (2) on systemic photon emission using one location for red filter exposure and another for photon emission recording. Photon emission of abdomen, forehead, palm, and dorsum of the hand was recorded before and after the presence of a red filter. In addition, photon emission of forehead and dorsum of the hand was recorded before, during, and after the presence of the red filter close to the palm. In both instances, the filter was dark-adapted and placed in close proximity to, but not touching the skin of the dark-adapted subject. A low-noise, end window photomultiplier for recording ultraviolet and visible (200-650 nm) photon emission (with a very low background count rate) and designed for manipulation in three directions was situated in a dark room. The technology was utilized to record spontaneous photon emission of the abdomen, forehead, palm, and dorsum of the hand of one human male subject. Data demonstrate that a dark-adapted subject responds in the total absence of light with a temporary increase in photon emission from the anatomic locations that had been exposed for 200 s at a distance of 3 cm to a dark-adapted red filter. Data from sequential time series suggest red filter initiation of a refractory emission reaction. Exposure of the palm to the red filter also evokes photon emission from the dorsum of the same hand and from the forehead. This response could be registered immediately after the beginning of the exposure. The stimulated emission is followed by a slow decrease of emission in the period after exposure to the filter. Data suggest that red filter-stimulated photon emission response is systemic and rapid. Data imply an exchange of information vis-à-vis light from both hand and red filter. The mechanism of such interaction is currently speculation only.

Angular Response of Photomultiplier Tubes: Photon-to-Electron Conversion Efficiency and Reflectance

Reflectance and photon-to-electron conversion efficiency have been measured for photomultiplier tubes (PMTs; Hamamatsu R878 and 7696) using three-color light-emitting diode (LED) emitting photons with central wavelengths of 470, 525, and 640 nm. The use of a light guide with a refractive index similar to that of a photomultiplier window enabled the measurement at the angle of incidence to a photocathode up to 75°. An appreciably large reflectance and conversion efficiency were obtained at the angles of approximately 45 and 60°, respectively. It was shown that these PMTs work with a higher photon-to-electron conversion efficiency than the quantum efficiency given by the manufacturer in many cases of scintillation counting. The reflectance measured in this study is consistent with that calculated using an optical model, where the photocathode was a thin film with a complex refractive index.

Color filters and human photon emission: Implications for auriculomedicine

Color filters are commonly utilized in auriculotherapy and auriculomedicine, diagnostic procedures based on the vascular autonomic signal (VAS) of the radial artery. It was reported that such effects were detectable in complete darkness. The human body emits ultraweak photons. It is hypothesized that there is feedback regulation of emission from the hand, implying an exchange of information vis-à-vis light from both hand and filter. To develop a research protocol for evaluating a possible effect of dark-adapted color filters on ultraweak human photon emission. Photon emission of the hand was recorded before, during, and after the presence of color filters. The filters were dark adapted and placed in close proximity but not touching the hand of the dark-adapted subject. SETTING AND PARTICIPANT: A specially selected, low-noise, end window photomultiplier for recording ultraviolet and visible (200-650 nm) photon emission (with a very low background count rate) designed for manipulation in three directions was situated in a dark room. The technology in the initial pilot series study was utilized to record spontaneous photon emission of the hand of one human male subject. The same series was repeated on the same subject three months later. The change in photon emission of the hand after exposure to single color filters was the main outcome parameter. Data demonstrate very similar responses for each of three different color filters. Data from consecutive time series suggest initiation of a refractory emission reaction. The response was dependent on the size of color surface and was neither detected with colorless transparent filters nor with nontransparent material.

Experimental-theoretical response of a ZnS(Ag) scintillating disc for gross-alpha measurements of aqueous radioactivity

A ZnS(Ag) scintillating disc coupled to a photomultiplier window tube was used to quantify the experimental detection efficiency of thick alpha sources and compare it with the theoretical detection efficiency. The experimental detection efficiencies were determined to be /spl sim/17%-18% for /sup 233/U and /sup 237/Np positioned 5.4 mm below the ZnS(Ag). The theoretical detection efficiency was calculated using an analytical model for an infinitely thick alpha source and was within 7% of the experimental values. In addition to these static measurements, online flow experiments were conducted. In these flow experiments, /sup 233/U wastewaters at three concentrations (14.19-53.65 Bq/mL) were quantified using the experimental detection efficiency and determined to be within 17%-18% of the expected concentrations. Pulse height analyses were performed for /sup 233/U spiked wastewater and for a 3700-Bq /sup 90/Sr solid point source. For a very low discriminator setting, the /sup 90/Sr//sup 90/Y detection efficiency was about 3.5%, which was reduced to essentially zero by raising the discriminator level by a minimal amount that did not effect the alpha detection efficiency. Additional experiments, which included /sup 233/U (34.66 Bq/mL) on MnO/sub 2/-coated glass fiber filter resulted in a detection efficiency of 22%-23%.

Measurement of absolute light yield and determination of a lower limit for the light attenuation length for YAP:Ce crystal

In small animal PET applications, the YAP:Ce scintillator has given some promising results. Because of its somewhat lower efficiency with respect to other PET crystals at 511 keV the depth of the crystal is a crucial parameter. Past measurements of the light attenuation length for YAP:Ce scintillator have given rather different results with values as low as 3 cm. We have studied the pulse height spectra of full energy absorption events as a function of the interaction distance from the photomultiplier window for five match like 2/spl times/2/spl times/30 mm/sup 3/ YAP:Ce crystals. Each crystal was covered on the four long sides and on one of the square section sides with a 5 /spl mu/m reflective layer. The crystals were the middle row of a bundle of 5 by 5 such crystals. By using a transport model for light within the crystals, for this crystal configuration, we obtained a lower limit of 6.8/spl plusmn/0.3 cm on the average 'bulk' (not including the losses from reflection) light attenuation length. This lower limit is significantly higher than the attenuation length measured by other authors. From these measurements and calculations, we have also determined the average absolute light yield for the five crystals to be 24000/spl plusmn/1400 photons/MeV.

Large-window gas proportional scintillation counter with photosensor compensation

New methods are presented that allow the design of non-focused gas proportional scintillation counters (GPSC) with window areas that approximate the photomultiplier window area. These methods are alternatives to a previously reported technique that uses a non-uniform electric field produced by a curved grid to compensate for the radial decrease of the scintillation light collected in the photosensor due to solid angle and reflection effects. The present work reverts to a uniform electric field and compensation is achieved with a mask with a radially-decreasing density of opaque dots that are deposited onto the window of the photosensor. The variation in the density of opaque dots is calculated to produce radially-independent light collection in the photosensor. An implementation of this new design is presented for a 52-mm-diameter photomultiplier tube with a 46-mm-effective diameter. The variation in pulse amplitude as a function of radial position was observed to be reduced from 18% to only 3.5% over the area contained within the central 19 mm radius. For a 38-mm-diameter window, the energy resolution for 5.9 keV X-rays was improved from 18% to 10% with the addition of the compensating mask.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A novel technique for scintillator light collection in neutron measurements

In time resolved measurements of neutron emission, the most common practice is to use a plastic scintillator coupled to a fast photomultiplier. There are different ways of coupling the light emitted by the scintillator to the photomultiplier (PM), according to the size and the shape of the scintillator. Some of the more usual coupling geometries are light pipes, Plexiglas cones with silvered walls or mirror ‘‘huts’’ facing the PM window.

Scintillation properties of lead sulfate

The material properties of lead sulfate (PbSO/sub 4/) are attractive for use as a gamma radiation detector. In 99.998% pure PbSO/sub 4/ crystals at room temperature excited by 511-keV annihilation photons, the fluorescence decay lifetime contained significant fast components having 1.8-ns and 19-ns decay times, but with longer components having 95-ns and 425-ns decay times. The peak emission wavelength was 335 nm, which was transmitted by borosilicate glass window photomultiplier tubes. The total scintillation light output increased with decreasing temperature from 3200 photons/MeV at +45 degrees C to 4900 photons/MeV at room temperature and 68500 photons/MeV at -145 degrees C. In an imperfect, 3-mm cube of a naturally occurring mineral form of PbSO/sub 4/ (anglesite) at room temperature, a 511-keV photopeak was seen with a total light output of 60% that of BGO. There was significant sample-to-sample variation of the light output among anglesite samples.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A protection circuit for side window photomultiplier tubes

A simple circuit to protect side window photomultiplier tubes against damage from accidental exposure to intense light is described. The gain of the tube is reduced by a factor of at least 104 within 20 μs of overload and automatically returns to normal when the over exposure is removed. This is achieved by using high voltage transistor optocouplers to reduce the voltage between the photocathode and the first seven stages of the tube to zero. The circuit may be easily adapted to suit other types of photomultiplier.

Simultaneous measurement of absorption and circular dichroism in a synchrotron spectrometer

We describe a method for simultaneously measuring the absorption spectrum and circular dicroism (CD) of a sample in a spectrometer that employs a transparent window photomultiplier detector. During the spectral scan, the computer control system simultaneously monitors the CD signal, the high voltage applied to the detector and the current in the storage ring. A servo-control system maintains the detector current at a constant value during the scan by varying the applied high voltage. The logarithm of the photomultiplier gain is calculated from the value of the high voltage using the predetermined characteristics of the tube. The gain value is corrected for the decrease of the storage ring current with time. During a single spectral scan, the computer generates a pseudo-absorption spectrum, which is the sum of the absorbance of the sample and of various wavelength-dependent system parameters. An absolute absorption spectrum is produced when the pseudo-absorption spectrum of a “blank” sample is subtracted from the desired sample spectrum. Absorption spectra measured by this method agree with spectra obtained with a double-beam spectrophotometer.

Photomultiplier window materials under electron irradiation: fluorescence and phosphorescence

The fluorescence and phosphorescence of photomultiplier window materials under electron irradiation have been investigated using a Sr(90)-Y(90) beta emitter as the electron source. Spectral emission curves of uv-grade, optical-grade, and electron-irradiated samples of MgF(2) and LiF, and of CaF(2), BaF(2), sapphire, fused silica, and uv-transmitting glasses were obtained over the 200-650-nm spectral range. Fluorescence yields, expressed as the number of counts in a solid angle of 2pi sr/MeV of incident electron energy deposited [MeV(-1) (2pi sr)(-1)], were determined on these materials utilizing photomultiplier tubes with cesium telluride, bialkali, and trialkali (S-20) photocathodes, respectively. Typical yields observed with a uv/visible sensitive bialkali cathode range from 10 MeV(-1) (2pi sr)(-1) for uv-grade MgF(2) to approximately 200 MeV(-1) (2pi sr)(-1) for CaF(2). For comparison, sodium-activated cesium iodide, one of the most efficient scintillator materials, yields about 700 MeV(-1) (2pi sr)(-1). High-purity fused silica has the lowest yield, approximately 6 MeVW(-1) (2pi sr)(-1). Optical-grade MgF(2)and LiF, as well as electron-irradiated uv-grade samples of these two materials, show enhanced fluorescence due to color-center formation and associated emission bands in the blue and red wavelength regions. Large variations in fluorescence intensities were found in uv-grade sapphire samples of different origins, particularly in the red end of the spectrum, presumably due to various amounts of chromium-ion content. Phosphorescence decay with time is best described by a sum of exponential terms, with time constants ranging from a few minutes to several days. Phosphorescence intensity expressed as a fraction of the steady-state fluorescence intensity is an extremely sensitive measure of crystalline perfection and purity. This fraction ranges from a high of approximately 10(-2) for some fluoride samples to a low of </=2 x 10(-6) for fused silica. Application of the parameters obtained in this work to the analysis of recent flight observations on low light-level experiments yields good quantitative agreement with flight data from OAO-3, OSO-7, and Apollo 17.

A Simple Nanosecond Gate for Side Window Photomultipliers and Echoes in Such Photomultipliers

A simple pulsing unit which gates on an inexpensive side window photomultiplier for 10–300 nsec with a rise time of 9 nsec is described. Following a strong pulse of light, a signal change of 1 part in 104 relative to the main pulse can be detected. Under low light conditions, the noise level is such that single photoelectrons can be detected. The performance of the system is shown in a measurement of light induced echoes in the photomultiplier which are 1000-fold weaker than the main signal.

Design of a simple liquid nitrogen cooled photomultiplier housing

A proven design of a simple and economical liquid nitrogen cooled photomultiplier housing for use with side window photomultiplier tubes is described.

Light Induced Concentration Changes of ATP From Phycomyces Sporangiophores: A Re-examination

Almost nothing is known about the biochemical steps involved in the light-induced growth responses of the sporangiophores of Phycomtyces blakesleeanus. In 1966, Shropshire and Gettens (3) reported results that seemed to show a local, transient increase of 30 % in extractable ATP caused by a saturating light pulse. In an attempt to exploit the exciting possibilities of this finding, one of us (KB) found that the significance of the results was questionable. Working together, the previous results could not be confirmed and, therefore, the original experiment was repeated on 8 separate days by one of us (WS). The sensitivity of the luciferin-luciferase assay for ATP was increased by the use of 0.05 M tris buffer (pH 7.8) in the luciferase extraction procedure (2) and 2-mercaptoethanol (5 X 10-5 miioles/mIl luciferase) in the reaction mixture (Colowick, personial communication). This modification resulted in a significant saving of the relatively costly and currently rationed firefly tails. The simple apparatus used to detect the initial light flash was assembled from a commercially available photoniultiplier light detector (Universal Photometer Model 201, Eldorado Electronics, 2821 Tenth Street, Berkeley, California). A cylindrical chamber with a lucite base for positioning reaction vessel test tubes over the photomultiplier window (modified from Hastings and Weber) (1) was constructed. The sporangiophores were cultured. stimulated. and extracted exactly as reported previously (3). Daily averages and standard deviations for the ATP content of sections cut from sporangiophores adapted to a constant light intensity and of sections cut from sporangiophores pulsed 15 seconds previously with a saturating light stimulus are shown in table I. Ten sporangiophore sections were used for each

A Total reflection X-Ray Spectrograph for Fluorescent Analysis of Light Elements

AbstractA novel x-ray spectrograph for the analysis of light elements has been developed based on previous computations and confirming experiments by one of as (H. K. Herglotz). The major components of the instrument are an efficient fluorescent source, a totally reflecting mirror, and an open window photomultiplier. Identification of wavelengths in the range 15 &lt; λ &lt; 80 Å is achieved by the wavelength dependence of the critical angle of reflection of an x-ray beam incident on a suitably chosen low absorption reflector. As the incident angle is increased through the critical angle for a particular wavelength, the reflected beam intensity is sharply reduced; hence, a periodic vibration of the incident beam through a small angular range about the critical angle furnishes a strong a.c. reflected signal characteristic of one narrow wavelength band only.Initial results promise a simple, easy-to-operate instrument for the routine analysis of elements boron to fluorine.

Solar observations with a soft x-ray spectrometer

A grazing incidence soft X-ray spectrometer designed for long-term operation in a satellite has been used for preliminary observation of the solar soft X-ray spectrum during an Aerobee rocket flight. The instrument employs a lightly ruled concave glass grating having a radius of curvature of one meter as the dispersing element. The resultant spectrum is scanned with a Bendix open window photomultiplier mounted behind the exit slit on a carriage which moves the assembly along the Rowland circle from 10 Å-400 Å. Wavelength calibration is obtained through observation of the carbon K emission band in the laboratory together with observation during flight of the He II Ly man-α line. A study of the reflecting power of the grating has been made which, together with an investigation of the efficiency of the detector now being planned, will provide an estimate of the instrumental efficiency at one or more wavelengths. Observations during a recent rocket flight indicate the presence of numerous emission lines in the wavelength region from 120 Å-400 Å. Tentative identification of lines produced by highly ionized atoms has been made.