Showing papers on "Photomultiplier published in 1993"

Optical filtering and spectral measurements of radiation-induced light in plastic scintillation dosimetry

Abstract: A small, water-equivalent plastic scintillation detector system has previously been developed for radiation therapy dosimetry. A light signal, proportional to dose, is generated in the scintillator and is transmitted to a remote photomultiplier tube (PMT) via optical fibres. Ionizing radiation also produces light in the fibres, which, if not properly accounted for, could limit the accuracy of the scintillator system. The fibre light is shown to have both a Cerenkov radiation and fluorescent component. The differences in the measured optical spectra of the fibre light and plastic scintillator light lead to the possibility of reducing the fibre light component by optical filtering. Optical spectral measurements of a commercially available orange-emitting plastic scintillator revealed that incomplete light-wavelength-shifting to the orange region of the visible spectrum occurs due to the size of the small scintillators that were used. Spectral measurements of orange and green scintillators with higher concentrations of wavelength-shifting fluor have been performed. Quantitative results indicate that using the highest doped orange scintillator and appropriate optical filter can decrease the fibre light contribution by about 50% when compared to the conventional blue scintillator, non-filtered case in typical radiotherapy dosimetry situations.

High sensitivity thermoluminescence spectrometer

Abstract: A high sensitivity thermoluminescence (TL) spectrometer capable of producing 3D isometric plots of TL intensity against wavelength and temperature is described. The use of multichannel detectors (imaging photomultiplier tubes) with matched gratings gives optimum detection efficiency for TL signals over a wide spectral range (200-800 nm), and at heating rates normally used for standard TL applications. Spectra have been recorded from dosimeter phosphors and minerals at low dose levels; several examples are given.

Scanning confocal microscope providing a continuous display

Abstract: A scanning confocal microscope scans a sample with an incident beam of radiation, in a raster scan pattern, causing the sample to fluoresce and emit visible radiation in at least two wavelengths. A portion of the fluorescent light retraces a portion of the path optical of incident beam, to a dichroic mirror that separates it from the incident beam for detection by a pair of photomultiplier tubes. A data processor accumulates digital data from the photomultiplier tubes to form a succession of image data frames of the sample being scanned, in the two wavelengths. Image data for a selected number of frames in each wavelength is averaged and then recorded on a single track of a recording system, in an alternating fashion with averaged data for the other wavelength. In addition, a ratio of the averaged data for the two wavelengths is delivered to a video display.

Hybrid photomultiplier tube with high sensitivity

Abstract: A focused electron/bombarded (FEB) ion detector comprising an MCP, focusing means, and a collection anode disposed in a detector body The collector anode includes a diode for receiving the focused output electron beam from the MCP The gain between the input ion current to the MCP and the detector output signal from the diode is on the order of 1-100 million, depending on the device configuration and applied biasing voltages A hybrid photomultiplier tube includes a photocathode, a photodiode for collecting and multiplying electrons emitted by the photocathode and providing an output signal and electrodes for focusing the electrons on the photodiode A vacuum envelope encloses a vacuum region between photocathode and the detector A conductor disposed on or adjacent to a sidewall of the vacuum envelope reduces the effect of electrical charges on the inside wall of the vacuum envelope on the trajectories of the electrons

Recent advances in the detection of optical photons with silicon photodiodes

Abstract: Geiger-mode avalanche photodiodes are interesting substitutes for conventional photomultiplier tubes in measurements of fast optical waveforms. In this paper we discuss the physical mechanisms involved in the detector operation and we clarify how these effects set a limit to the achievable timing performance. We show that a proper choice of the electric field profile is mandatory for the design of devices combining high quantum efficiency and timing resolution given by the ultimate transit time limit.

Improvement of 20 in. diameter photomultiplier tubes

Abstract: The quality of the 20 in. photomultiplier tubes (Hamamatsu R1449) has been greatly improved over the required specifications for using them in the 50 000 ton imaging water Cherenkov detector, Super-Kamiokande. In particular, the resolution of the timing response for single-photoelectron light has been reduced to ∼ 3 ns (1σ width), and a clear single-photoelectron peak can be seen in the pulse height distribution. The obtained characteristics of the new tubes will make it possible to upgrade the performance of the Super-Kamiokande detector. The goal of the improvement, the procedure for designing the new tubes and the measuring results concerning the characteristics are described in detail.

Performance of the inverse photoemission spectrometer with a new bandpass photon detector of narrow bandwidth and high sensitivity

Abstract: A combination of a SrF2 entrance window and a photomultiplier with the CuBeO first dynode coated with KCl film realizes the bandpass photon detector with the FWHM of 0.47 eV centered at 9.43 eV and the sensitivity improved by about one order of magnitude in comparison with the detector without the KCl film. The overall energy resolution of the inverse photoemission spectrometer consisting of an electron gun with a BaO cathode and the new detector has been estimated to be 0.56 eV using polycrystalline Au. Typical counting rate is 102-103 counts/(μA s) for unoccupied states near the Fermi level of the Au at an acceptance angle of about 0.8π sr with an Al collecting mirror.

Timing characteritics of a micro-channel plate and fine mesh photomultiplier tubes in a 1 T field

Abstract: Timing characteristics of a micro-channel plate (MCP) and a fine mesh (FM) photomultiplier tubes were investigated in magnetic fields up to 1.5 T as functions of the field strength and direction. The r.m.s. values of transit time spread of the MCP and the FM tubes in 1 T field were found to be 40 ps and 140 ps, respectively. For a simulated scintillation light equivalent to 160 photoelectrons, the FM tube gave a time resolution better than 100 ps even in a 1 T field in spite of a large gain reduction to less than a 10%.

Characterization of a pulsed X-ray source for fluorescent lifetime measurements

Abstract: To search for new, fast, inorganic scintillators, we have developed a bench-top pulsed X-ray source for determining fluorescent lifetimes and wavelengths of compounds in crystal or powdered form. This source uses a light-excited X-ray tube which produces X-rays when light from a laser diode strikes its photocathode. The X-ray tube has a tungsten anode, a beryllium exit window, a 30 kV maximum tube bias, and a 50 /spl mu/A maximum average cathode current. The laser produces 3/spl times/10/sup 7/ photons at 650 nm per /spl sim/100 ps pulse, with up to 10/sup 7/ pulses/sec. The time spread for the laser diode, X-ray tube, and a microchannel plate photomultiplier tube is less than 120 ps fwhm. The mean X-ray energy at tube biases of 20, 25, and 30 kV is 9.4, 10.3, and 11.1 keV, respectively. We measured 140, 230, and 330 X-ray photons per laser diode pulse per steradian, at tube biases of 20, 25, and 30 kV, respectively. Background X-rays due to dark current occur at a rate of 1/spl times/10/sup 6/ and 3/spl times/10/sup 6/ photons/sec/steradian at biases of 25 and 30 kV, respectively. Data characterizing the X-ray output with an aluminum filter in the X-ray beam are also presented. >

Operational characteristics of an electron-bombarded silicon-diode photomultiplier tube

Abstract: An electron-bombarded silicon-diode photomultiplier tube (EDPMT) has been constructed and the first experimental data on operational characteristics are presented. The signal multiplication of this tube is, in contrast to the traditional PMT, not accomplished by multiplying the number of photo-generated electrons, but by increasing each electron's energy 3–4 orders of magnitude. The relative simplicity of design properties make this type of tube an attractive alternative for many applications. This tube has small size, low mass, it is robust and it incorporates a low cost electron multiplier. Also, it only requires a single negative high voltage connection, without a voltage-divider, and a low voltage diode reverse-bias connection, which greatly reduces the power supply requirements for large scale operations such as those at CERN, Fermilab, and the Superconducting Supercollider.

A photomultiplier tube incorporating an avalanche photodiode

Abstract: A photomultiplier tube incorporating an avalanche photodiode operated in the electron bombardment mode has been developed and tested. It has a large linear dynamic range, can operate with gains up to 10 6 , is unaffected by axial magnetic fields and has been measured to have excellent timing properties. Different versions of the tube were made with bialkali, multi-alkali, and negative electron affinity photocathodes, in this paper we will report on results obtained with these different types of photocathodes. This type of PMT will be useful for applications where large dynamic range and high quantum efficiencies are required. The extension of this concept to a multichannel device with a segmented APD array will provide an economical readout for both fiber tracking and calorimetry applications. A tube equipped with such an array is being developed currently as a readout option for the SDC shower maximum detector.

Simulation of imaging with sodium iodide crystals and position-sensitive photomultiplier tubes

Abstract: The imaging characteristics of miniature gamma cameras that consist of a single sodium iodide (NaI(Tl)) crystal coupled to a position-sensitive photomultiplier tube (PSPMT) have been studied via Monte Carlo simulations. Images obtained with such cameras with the use of conventional position calculations exhibit considerable distortions, particularly compression. This study demonstrates that the distortions result primarily from nonuniform sensitivities of PSPMTs and secondarily from nonlinear responses of PSPMTs, light-reflection properties resulting from the treatments of crystals, and light-refractive properties of glass interfaces between crystals and photocathodes. Simulation results are compared to images obtained with a prototype miniature gamma camera. >

Photomultiplier assembly and gamma camera head

Abstract: A photomultiplier assembly for use in gamma cameras, etc., includes an array of head-on type photomultipliers (112) disposed in parallel relation to one another. The array of the photomultipliers has a plurality of dead spaces (138), in which reflectors (140) are respectively disposed. The reflector can reflect light, which has entered the corresponding dead space, to an upper portion of a side wall of the near photomultiplier. A side photocathode surface (126) is formed on an inside surface of the upper portion of the side wall of the photomultiplier. Therefore, the light which has entered the dead space is reflected by the reflector and impinges on the side photocathode surface to be converted into photoelectrons.

Quantum efficiencies of several VUV-sensitive photomultiplier tubes☆

Abstract: The quantum efficiencies (QEs) of several VUV sensitive photon detectors were determined and compared with each other. We tested the following photomultiplier tubes (PMTs): five Philips XP2020Qs, one Hamamatsu R2059, and one Thorn EMI 9426. We also tested a Na-salicylate coated glass window combined with a Philips XP2020 PMT. At wavelengths smaller than 230 nm, the QEs of both the Thorn EMI and Philips PMTs appear significantly better than the QE of the Hamamatsu PMT. Furthermore, at these wavelengths, the QE of the XP2020Q PMTs was found to be much higher than advertised in the manufacturers catalogues.

Photomultiplier tube of new dynode configuration

Abstract: In spectroscopic analysis, radiation detection, and medical application fields, portable instruments requiring high accuracy and high sensitivity are being developed. Since conventional photomultiplier tube (PMT) envelopes are made of glass and are large in size, it is difficult to downsize instruments. PMTs are mainly used for high accuracy instruments, while solid state detectors are employed for general purpose, or compact instruments. Hamamatsu recently developed the compact PMT R5600 series, which is downsized to the same dimensions as a solid state detector while maintaining the same performance, high sensitivity and high speed as the conventional PMTs. >

Prospects for new fast photomultipliers

Abstract: Comparative studies of the time resolution measured with the XP2020, XP2020UR and the XP2020UR-M modified by a screening grid at the anode were carried out for three different scintillators: a small NE111, a medium size NE213 and for a NaI(Tl) crystal. Compared to the XP2020 an important progress in timing with the XP2020UR was shown, due to its lower time jitter, however, mainly observed with the small NE111 plastics. The modified XP2020UR-M represents a further remarkable improvement of the time resolution over the XP2020UR by a factor of 1.14, independently of a type of the scintillator used (fast plastic or NaI(Tl)). The analysis of the experimental data suggest strongly that this method can be successfully applied to all fast photomultipliers, independently of their time jitter. The observed limitation of the time resolution measured with the intensive fast light pulses from the NE111 plastic at 1 MeV energy seems to be associated with the space charge effect in the dynode structure due to low interstage voltages. It thus suggests a photomultipliers construction with a reduced number of dynodes. Finally, the study defines requirements addressed to the future fast photomultipliers which would bring improvement of the time resolution over the XP2020UR by a factor of about 1.3.

Performances of the photomultiplier EMI 9351 for underground physics applications

Abstract: In this article we discuss the results of tests performed on the 8 in. EMI 9351 photube. The measurements were mainly devoted to evaluate pulse height and time resolution of the tube after single photon illumination. The impact of small magnetic fields on these parameters was also carefully investigated.

Detectors for scanning video imagers.

Abstract: Detectors for scanning video (10-MHz) imagers should be chosen for their high quantum efficiency and internal gain. Because of the high bandwidth both photomultiplier tubes and avalanche photodiodes are limited by photon noise, so that dark noise is not the determining quantity.

Remote gain control circuit for photomultiplier tubes

Abstract: A gain control circuit (10) for remotely controlling the gain of a photomultiplier tube (PMT (12)). The remote gain control circuit (10) may be used with a PMT (12) having any selected number of dynodes (DY). The remote gain control circuit (10) is connected to the last dynode nearest the anode (16) in the dynode string which controls the total dynode supply voltage and influences the gain of each dynode (DY). The remote gain control circuit (10) of the present invention includes an integrated-circuit operational amplifier (U1), a high-voltage transistor (Q1), a plurality of resistors (R), a plurality of capacitors (C), and a plurality of diodes (D). Negative feedback is used to set the last dynode voltage proportional to a voltage controlled by the gain control voltage delivered by a voltage source such as a digital-to-analog converter. The control circuit (10) of the present invention is connected to the last dynode using a single connecting wire (22).

Timing properties of Philips XP2020UR photomultiplier

Abstract: The timing properties of scintillation counters consisting of small NE111 plastic scintillators coupled to the XP2020UR photomultipliers have been studied in comparison to that based on the XP2020. The time jitter of both the photomultipliers, their photoelectron yield for the NE111 plastics and the time resolution with 60Co and 22Na sources were measured. A high time resolution was achieved with the XP2020UR equal to 90 ps for 60Co (at 1 MeV) and 140 ps for 22Na (at 290 keV) energy settings, about 30% and 20% better respectively than those observed with the XP2020. The large improvement of the time resolution is due to: 30% lower time jitter, about 25% higher photoelectron yield and for the 60Co energy settings also to a reduced influence of the space charge effect in the XP2020UR. The normalised time resolution to the photoelectron number, measured with 22Na source, is better by a factor of 1.14 which corresponds well to the improvement of the time jitter in the new XP2020UR photomultiplier.

Wire chambers revisited

Abstract: Detectors used for radioisotope imaging have, historically, been based on scintillating crystal/photomultiplier combinations in various forms. From the rectilinear scanner through to modern gamma cameras and positron cameras, the basic technology has remained much the same. Efforts to overcome the limitations of this form of technology have foundered on the inability to reproduce the required sensitivity, spatial resolution and sensitive area at acceptable cost. Multiwire proportional chambers (MWPCs) have long been used as position-sensitive charged particle detectors in nuclear and high-energy physics. MWPCs are large-area gas-filled ionisation chambers in which large arrays of fine wires are used to measure the position of ionisation produced in the gas by the passage of charged particles. The important properties of MWPCs are high-spatial-resolution, large-area, high-count-rate performance at low cost. For research applications, detectors several metres square have been built and small-area detectors have a charged particle resolution of 0.4 mm at a count rate of several million per second. Modification is required to MWPCs for nuclear medicine imaging. As gamma rays or X-rays cannot be detected directly, they must be converted into photo- or Compton scatter electrons. Photon-electron conversion requires the use of high atomic number materials in the body of the chamber. Pressurised xenon is the most useful form of “gas only” photon-electron convertor and has been used successfully in a gamma camera for the detection of gamma rays at energies below 100 keV This camera has been developed specifically for highcount-rate first-pass cardiac imaging. This high-pressure xenon gas MWPC is the key to a highly competitive system which can outperform scintillator-based systems. The count rate performance is close to a million counts per second and the intrinsic spatial resolution is better than the best scintillator-based camera. The MWPC camera produces quantitative ejection fraction information of the highest quality. The detection of higher energy gamma rays has proved more problematical, needing a solid photon-electron convertor to be incorporated into the chamber. Several groups have been working on this problem with modest success so far. The only clinical detectors have been developed for positron emission tomography, where thin lead or lead-glass can provide an acceptable convertor for 511 keV photons. Two MWPC positron cameras have been evaluated clinically and one is now in routine use in clinical oncology. The problems of detection efficiency have not been solved by these detectors although reliability and large-area PET imaging have been proven. The latest development involves a hybrid system in which crystals of barium fluoride are viewed by an MWPC filled with a photosensitive gas. The high detection efficiency of the scintillator is combined with the large sensitive area and good spatial resolution of the MWPC to overcome the limitations of previous MWPC-based positron cameras. The first large-area, clinical camera using this technology is now under development and is expected to perform at least as well as multicrystal positron cameras but at a fraction of the cost.

A phototube RICH detector

Abstract: The results from a prototype for a fast RICH detector using phototubes are presented, testing three different types of tubes in the photocathode In a 400 GeV/ cπ − beam, the number of photons detected was 118 per ring and the ring radius resolution obtained was 113% The figure of merit, N 0 , for the entire photocathode was measured to be 93/cm Particle identification as a function of beam momentum was studied, as well as multiparticle event recognition

Phoswich detectors having optical filter for controlling pulse height and rise time of output from scintillator

Abstract: A phoswich detector having two or more scintillators is disclosed, in which at least one optical filter is provided between the scintillator farthest from a photomultiplier and the scintillator nearest to the photomultiplier. The detector is capable of reducing the pulse height of signal from the scintillator to an arbitrary level and extending the rise time of the pulse to some extent.

Radiation imaging device having an enlarged uniform field of view

Abstract: A radiation imaging device of the type employing a scintillator and a position-sensitive photomultiplier tube eliminates or reduces edge effects and thereby increases the linear field of view by compensating for nonlinearities which distort an image close to the edge. Specifically, (1) a light guide is placed about the edge of the scintillator to channel light that would otherwise be reflected from the edge of scintillator to a light absorbing material so that edge reflected light is not detected by the position-sensitive photomultiplier tube and (2) variable resistors are employed to compensate for distortions in the image caused by current leakage along the edge of the position-sensitive photomultiplier tube.

Gas proportional scintillation counter for ionizing radiation with medium and large size radiation windows and/or detection volumes

Abstract: The present invention concerns detectors for ionizing radiation (X-rays, gamma rays, electrons, protons, alpha particles, etc. as well as neutrons) of the gas proportional scintillation counter type. The preferred embodiment for X-ray detection consists in a detector, filled with very pure xenon at atmospheric pressure, with a 2.5 cm diameter radiation window (1), a grid with a spherical (2 cm radius) curvature (2) with its edges placed 0.8 cm away from a plane grid which is placed in contact with or close to a photomultiplier tube (4). This photomultiplier has uniform sensitivity in the 170 nm wavelength region. This detector presents an energy resolution of 8.0 % for 5.9 keV X-rays.

New concepts for scintillator/HgI/sub 2/ gamma ray spectroscopy

Abstract: The construction of a high energy resolution gamma ray detector consisting of a scintillator/mercuric iodide photodetector combination has been investigated. Several HgI/sub 2/ photodetectors have been fabricated and tested with standard NIM electronics. The energy resolution of a scintillator/HgI/sub 2/ pair was found to be 4.75%, full width at half maximum, for 662 keV /sup 137/Cs gamma ray photons. Of five detectors fabricated with our new technique, all produced resolutions better than 5.6% FWHM. This technology makes it possible to reliably produce high quality HgI/sub 2/ photodetectors. New design concepts for the HgI/sub 2/ photocell, including the transparent entrance electrode, detector geometry, and detector packaging, are described in the paper. Advantages of gamma ray spectrometers based upon crystal scintillators optically coupled to HgI/sub 2/ photodetectors (in contrast to coupling the scintillators to the more conventional light sensors, i.e., photomultiplier tubes (PMTs)) include greater ruggedness, improved energy resolution, markedly smaller size and weight, reduced power, and insensitivity to magnetic field perturbations. >

400-ps time resolution with a passively quenched avalanche photodiode

Abstract: Avalanche photodiodes (APD’s) operated in a single-photon-counting Geiger mode are becoming attractive alternatives to photomultiplier tubes for low-light-level detection and signal timing. By paying careful attention to the design and construction of a simple APD passive quenching circuit to reduce stray capacitances, we directly measured a time resolution of 410 ps FWHM for a commercial APD. A more detailed data analysis shows the actual time resolution to be ~ 390 ps FWHM. This is believed to be the most accurate time response for such a simple, inexpensive, and widely available device achieved to date.

Numbers of scintillation photons produced in NaI(Tl) and plastic scintillator by gamma-rays

Abstract: The W/sub S/-value, which is defined as an average energy expended per scintillation photon, is determined to be 17.2+or-0.40 eV for a NaI(Tl) phosphor and 60.8+or-4.3 eV for a plastic scintillator (NE-102A). These are obtained from the numbers of photoelectrons measured with several combinations of a photomultiplier tube and a NaI(Tl) or a NE-102A scintillator. The number of photoelectrons, which are measured by the photomultiplier tube as a vacuum photodiode, are converted to the number of scintillation photons by using an averaged quantum efficiency of each photomultiplier photocathode and a calculated collection efficiency of the scintillation photons at the photocathode. The above values do not include the uncertainties due to the unknown exact emission spectra and the photomultiplier response curves. >

A time-of-flight array for 1 to 2 GeV/c particles

Abstract: A time-of-flight detector array has been developed for an experiment searching for the strangeness −2 H-particle. The array consists of 40 logs of plastic scintillator with dimensions 2.00 × 0.085 × 0.050 m3. The photomultiplier tubes are coupled to the scintillators without the use of light guides, and the mounting of the bars is designed for easy adjustment and servicing. The average intrinsic time resolution was found to be 110 ps σ.