Showing papers on "Photomultiplier published in 1997"

A microoptode array for fine-scale measurement of oxygen distribution

Abstract: A new microoptode array is presented that provides simultaneous measurement with eight oxygen microoptodes using a simple optical setup and a phase-angle detection principle. The measuring system consists of: (1) an optical unit with eight oxygen microoptodes, a special fiber-coupler array, optical filters, lenses, light sources (light-emitting diodes) and light detectors (photodiodes, photomultiplier tube); (2) a signal-processing unit with analog signal processing (phase-angle detection, filtering) and digital signal processing (control, data storage and display). The oxygen concentration is measured with tapered silica-glass fibers (tip diameter 20–30 μm) by the dynamic quenching of a luminophore. A phase-modulation technique is used to determine the phase-angle shift that is caused by the fluorescence lifetime when the indicator is excited sinusoidally. In a time multiplex mode each sensor signal is sampled. This multisensor array system is designed for the investigation of the oxygen distribution in biofilms and aquatic sediments. The new measuring system and first applications in artificial and natural systems are presented.

Photon detection with high gain avalanche photodiode arrays

Abstract: The detection of light emitted in fast scintillating fibers and Cerenkov radiators used for fiber calorimetry and tracking applications in high energy colliders, requires fast detector arrays with high sensitivity to short wavelength photons. Photomultiplier tubes, the traditional imaging detectors for short wavelength optical radiation, have limited spatial resolution and require expensive anti-magnetic shielding. We report on short wavelength sensitivity improvement and detection efficiency performance for a novel p-n junction planar structure silicon avalanche photodiode (APD) array, operated in Geiger mode. The APD array provides a high sensitivity detector for applications requiring the detection of light spatial distributions with single photon sensitivity.

A new type of multiparticle three-dimensional imaging detector with subnanosecond time resolution

Abstract: A new type of multiparticle three-dimensional imaging detector for the measurement of kinetic energy releases in molecular dissociation processes is presented. The detector makes use of the new generation of multianode photomultipliers to produce a timing signal for the simultaneous impact of several particles on the surface of a microchannel plate coupled to a phosphor screen. The detector is capable of subnanosecond time resolution (about 100 ps for the present setup) and position resolution (using a standard charge-coupled-device camera) of about 100 μm. The detector is suitable for ultrahigh-vacuum operation and can work with particles over a range of kinetic energies from keV to MeV.

Characterization of a 64 channel PET detector using photodiodes for crystal identification

Abstract: The authors present performance results for a prototype PET detector module consisting of 64 LSO scintillator crystals (3/spl times/3/spl times/20 mm) coupled on one end to a single photomultiplier tube and on the opposite end to a 64 pixel array of 3 mm square silicon photodiodes (typical pixel parameters are 5 pF capacitance, 300 pA dark current, and 73% quantum efficiency at 415 nm). The photomultiplier tube (PMT) provides an accurate timing pulse and energy threshold for all crystals in the module, the silicon photodiodes (PD) identify the crystal of interaction, the sum (PD+PMT) provides a total energy signal, and the PD/(PD+PMT) ratio determines the depth of interaction. With 32 of the channels instrumented, the detector module correctly identifies the crystal of interaction (where "correct" includes the adjacent 4 crystals) 79/spl plusmn/4% of the time with high detection efficiency. The timing resolution for a single LSO detector module is 750 ps fwhm, while its pulse height resolution at 511 keV is 24/spl plusmn/3% fwhm. The depth of interaction measurement resolution is 8/spl plusmn/1 mm fwhm.

Voltage division circuit for a photomultiplier tube

Abstract: A voltage division circuit for a photomultiplier tube in which an electron multiplication factor of the photomultiplier tube is readily changeable in a wide range with a low power consumption and without degrading a dynode's collection efficiency and an output linearity. The voltage division portion 100 divides a high voltage (-HV) at a fixed voltage division ratio determined by the resistance values of resistors 111 to 116, 121 and 122, and 131 to 134 to thereby generate voltages applied to a focusing electrode 820, dynodes 831, 832 and 836 to 838. Another voltage division portion 300 includes a variable resistor 332 and generates voltages applied to the dynodes 833 to 835 by dividing the high voltage at a variable voltage division ratio upon operating the variable resistor.

Construction and calibration of detectors for high-resolution metabolic breast cancer imaging

Abstract: Each of two detectors used in our Positron Emission Mammography (PEM) system consists of four 36 mm × 36 mm × 20 mm bismuth germanate (BGO) crystal detector blocks coupled to a crossed-wire anode position-sensitive photomultiplier tube (PS-PMT). To facilitate high spatial-resolution imaging, the crystal blocks have been finely pixelated using a diamond saw. In each detector, 36 × 36 1.9 mm × 1.9 mm crystal elements are coupled directly to the PMT window and, on the opposite face of the blocks, 35 × 35 elements are offset by 1.0 mm along both the x- and y-axis of the PS-PMT. As part of a system calibration routine, a novel method for crystal element identification has been developed. This algorithm successfully identifies 59 × 49 crystal elements on each detector face. These results are used to generate a Look-Up-Table (LUT) that is accessed during image formation for the effective correction of spatial distortion inherent in the detectors. Crystal identification also facilitates the capability for accurate energy discrimination, since the detector gain is considered on an element-by-element basis by accesing an energy LUT. Employing a third LUT, which contains the relative efficiencies of individual crystal elements results in improvement in image uniformity from 50% to 13%.

Design features and performance of a CsI(Na) array based gamma camera for small animal gene research

Abstract: The authors report on the development of a radiation imaging system based on a matrix of CsI(Na) scintillating crystals. This detector system has been optimized for high resolution radiation imaging of the distribution of iodine 125 (/sup 125/I) in a laboratory animal. The radioisotope /sup 125/I is readily available as a label to molecular biology probes that can be used in gene research. Iodine 125 decays via electron capture emitting a 35 keV gamma-ray with the prompt emission of several 27-32 keV X-rays. A coincidence condition can be set to detect the /sup 125/I decays thus reducing background radiation contribution to the image. The system utilizes the Hamamatsu 5 inch diameter 3292 position sensitive photomultiplier tube (PSPMT) coupled to the CsI(Na) matrix and a custom built high resolution copper-beryllium collimator. A conventional photomultiplier coupled to a NaI(Ti) crystal scintillator is used to detect the coincident radiation resulting from the decay of /sup 125/I.

Method and apparatus for a directional neutron detector which discriminates neutrons from gamma rays

Abstract: Apparatus and method for discriminating against neutrons coming from directions other than a preferred direction and discriminating against gamma rays. Two photomultiplier (PM) tubes 9,10 are parallel to each other and are attached to one end of a light pipe 12. A neutron scintillator 13 is attached to the other end of the light pipe. The scintillator 13 is comprised of optical fibers arranged contiguously along a first direction, which is perpendicular to a length dimension of the optical fibers, and which optical fibers alternate between optical fibers which emit photons only in the lower portion of the electromagnetic spectrum and optical fibers which emit photons only in the higher portion of the electromagnetic spectrum. Typically, the optical fibers are about 100-250 microns. Filters 7,8 are between the PM tubes and the light pipe. One filter 7 transmits only photons in the lower end of the electromagnetic spectrum and the other filter 8 transmits only photons in the higher portion of the electromagnetic spectrum. Neutrons proceeding from a source which is parallel to the first direction will tend to cause only one optical fiber to emit photons. If neutrons enter the scintillator perpendicular to such first direction, photons will most likely be emitted by more than one optical fiber. A signal processing unit 11 will register a detected neutron if a signal is received from only one PM tube and will register a background event if signals are received from both PM tubes. If a gamma ray enters the detector and is detected, the scattered Compton electron most likely will cross two or more optical fibers, causing signals in both PM tubes. A signal processing unit 11 will register the event as a background event.

Bandpass photon detector

Abstract: Apparatus for bandpass photon detection containing a lens for collimating input light, a bandpass filter element, and a photomultiplier detector. Light passes from a source into the lens which collimates the light which then is incident upon the filter. The filter is tuned to a particular band of wavelengths, such that out of all of the wavelengths that are incident upon the front side of the filter, a wavelength band is propagated through the filter and passes from the filter to the photomultiplier detector, such that the output of the photomultiplier detector is a voltage level representing the energy content within that wavelength band. In various alternative embodiments, the bandpass photon detectors are arranged in a number of cascade arrangements such that multiple wavelength bands are simultaneously detected.

Performance study of liquid xenon detector for PET

Abstract: The coincidence time resolution and the intrinsic position resolution along the electron drift direction of a liquid xenon multiwire ionization chamber for PET were measured, being, respectively, 15 ns (fwhm) and 05 mm (fwhm) Data on the low temperature performance of a photomultiplier tube operating on the VUV are presented

Tests of a multianode PMT for the HERA-B RICH

Abstract: A new multianode photomultiplier tube, type H6568 manufactured by Hamamatsu company, has been tested in view of using it for measuring Cherenkov rings in the HERA-B experiment. The results of measurements of single-photoelectron pulse-height distributions, uniformity of response, cross-talk, photon detection efficiency, rate dependence of the gain and ageing will be presented and discussed. In addition, the response of the PMT to scintillations of perfluorobutane (C 4 F 10 ), argon and air has been measured.

Photon counting III-V hybrid photomultipliers using transmission mode photocathodes

Abstract: This paper reports on the development of solid-state hybrid photomultiplier tubes using high quantum efficiency, transmission mode, III-V photocathodes. The first strike low-noise gain mechanism in these devices is provided via electron bombardment of a solid-state GaAs Schottky diode. In addition, a second-stage gain is provided by solid-state avalanching within a GaAs Schottky APD (SAPD) anode. A combined gain of 2/spl times/10/sup 4/, adequate for photon counting, is achieved. Device bandwidth, exceeding 1 GHz, is optimized by tailoring the diode anode structure. The combined traits of this device provide high quantum efficiency, large dynamic range, large bandwidth, and adequate gain for photon counting. Photon counting beyond 1 /spl mu/m is feasible for a cooled device. The tube structure, diode anode structure, noise issues and preliminary photon counting results are discussed.

On the influence of afterpulsing in PMTs on the trigger threshold of multichannel light detectors in self-trigger mode

Abstract: In some experiments photomultiplier based multichannel detectors are used to measure short light flashes in self-trigger mode in the presence of a significant background illumination. This background can induce a sizeable afterpulse rate. Contrary to published data the afterpulses can have rather large amplitudes and might be interpreted as genuine signals. This is the case with current imaging air Cherenkov telescopes in cosmic ray experiments. We found that due to the simple trigger logic of contemporary telescopes it is not the light of the night sky (LONS), but the afterpulsing which sets the trigger threshold. Afterpulsing features for 5 types of photomultiplier tubes are presented.

New generation position-sensitive PMT for nuclear medicine imaging

Abstract: Recently, Hamamatsu has developed a new dynode structure in a position-sensitive photomultiplier tube (PSPMT) based on metal channel technology, producing a very focused charge distribution. Hamamatsu R5900-C8 is the first metal channel dynode PSPMT with a crossed wire anode. The outline dimension is 28 × 28 × 20 mm3 with an active area of 21 × 22 mm2 and four wire anodes (4X + 4Y). A weighted summing device was realised to calculate the charge distribution centroid where each anode was directly connected to a preamplifier and amplifier. Tests of position linearity, energy response and spatial resolution were carried out coupling the PSPMT to an NaI(Tl) planar crystal and to a YAP:Ce scintillation array. To test the influence of charge spread on position linearity, the photocathode was irradiated by a light spot with 1 mm of aperture size. Position non-linearity resulted when a scintillating array with 1 × 1 mm2 pixel size was coupled to PSPMT. On the contrary, increasing the spread of charge distribution by a planar scintillation crystal, a good linearity response was obtained. Impressive spatial resolution values were obtained from the YAP:Ce scintillating array. They ranged between 0.5 and 0.2 mm irradiating the crystals by 57Co and 137Cs source, respectively.

Support assembly for scintillating crystal

Abstract: A gamma camera includes at least one detector assembly 10. The detector assembly includes an array of photomultiplier tubes, a sheet of scintillating crystal material, a sheet of optical glass, and a matrix of mu-metal material. The mu-metal matrix defines an array of apertures corresponding to the array of photomultiplier tubes into which apertures the photomultiplier tubes are inserted. The scintillating crystal is bonded to the first surface of the optical glass. The mu-metal matrix is connected to the second surface of the sheet of optical glass using an adhesive such as an epoxy cement. By integrating the metal matrix into the structure formed by the glass sheet and the crystal, the glass sheet may be made thinner than before while the crystal is supported against possible bending and consequent fracture.

Evaluation of multi-channel PMTs for readout of scintillator arrays

Abstract: We have evaluated two Philips multi-channel photomultiplier tubes (MC-PMTs) as position-sensitive photon detectors for reading out small scintillator arrays. The 64 channel XP1702 MC-PMT has a standard glass entrance window while the XP1722 model has a fibre-optic entrance window designed to reduce inter-channel crosstalk. Scientillator arrays are coupled typically to these MC-PMTs using optical fibers. In this paper, we present measurements of inter-channel gain variation, pixel-to-pixel crosstalk, single photoelectron spectra, MC-PMT linearity and sensitivity to magnetic fields. For both the XP1702 and XP1722 models, the maximum-gain variation over all 64 channels is typically 3:1, while the difference between any two adjacent channels is less than 2:1. Crosstalk to the nearest neighbor is 10% for the fiber-optic input window tube compared with 20% for the glass input window tube and is relatively insensitive to the size and numerical aperture of the optical fiber used. The output of the 10th dynode (position signal) remains linear up to 400 photoelectrons at a gain of 4 × 106 using a Philips VD 107 voltage divider. Performance in a magnetic field was found to depend strongly on the orientation of the tube relative to the field. Images obtain with a 511 keV source irradiating an 8 × 8 array of 2 × 2 × 10 mm BGO crystals coupled by optical fiber to these tubes show excellent crystal identification, particularly using the XP1722 MC-PMT.

An ultraviolet nanosecond light pulse generator using a light emitting diode for test of photodetectors

Abstract: An optical function pulse generator that emits (1) short pulse of 1 ns duration, (2) double pulse with variable time interval, and (3) square waveform pulse of variable width in nanosecond range is devised using an InGaN/AlGaN double heterostructure light emitting diode (LED). Although the LED emits a 450 nm (blue) light under conventional dc operation below 30 mA, 380 nm light due to the InGaN/AlGaN component appears when a current larger than 50 mA is applied. This phenomenon is used to realize a pulsed ultraviolet light source. Under large nanosecond current pulsing (peak current >1 A), an intense pulsed emission of 380 nm is obtained. Pulse waveform of the LED emission can be adjusted electrically by applying a shaped current to the LED. To evaluate the potential of the pulse generator as a test source of photodetectors, the response waveforms of photomultiplier tubes were measured.

Study on fine-mesh PMTs for detection of aerogel Cherenkov light

Abstract: Most recent fine-mesh photomultipliers (FM-PMTs), with 19 dynode stages, have been tested for application to a threshold aerogel Cherenkov counter. Two properties, the gain and the pulse height resolution, have been particularly studied in a magnetic field of up to 1.5 T. The obtained results show that a FM-PMT is a suitable device for detection of aerogel Cherenkov light.

Light spectra sum rule

Abstract: Fourier analysis is applied to a statistical model of photon detector behaviour. An interesting sum rule relating the characteristic function for photoelectron spectra and for the single electron response function is derived. This suggests the design of new strategies for photoelectron spectra analysis. Some of them are described in the case of experiments performed with electrostatically focused hybrid photomultiplier tubes.

Photomultiplier tube with focusing electrode plate

Abstract: In the electron multiplier assembly 27, a dynode unit 10 is constructed from a plurality of dynodes 9 laminated one on another. Each dynode 9 is formed with multichannels 12 which are separated from one another by channel-separating portions 14. A focusing electrode plate 16 is formed with multichannels 18 which are separated from one another by channel-separating electrodes 20 which are located in correspondence with the channel-separating portions 14 of the first stage dynode 9a. A plurality of anodes 7 are provided for receiving electrons multiplied at the dynode unit 10 in their corresponding channels 18. Each channel-separating electrode 20 is formed with an opening 21, at a position confronting the channel-separating portion 14 of the first stage dynode 9a, for transmitting electrons therethrough.

Low temperature performance of photomultiplier tubes illuminated in pulsed mode by visible and vacuum ultraviolet light

Abstract: Detecting the ultraviolet scintillation light of the liquefied rare gases, in particular liquid xenon, requires the use of photomultiplier tubes (PMTs) in a temperature range where their operation is not ensured by manufacturers. Simultaneously, monitoring of the PMTs should be done in the visible for technical reasons. Bialkali photocathodes, that present high quantum efficiency and low dark noise, exhibit a very strong increase of electrical resistivity upon cooling that, apart from other reasons, can lead to operation failure at low temperature. Photomultiplier tubes with bialkali photocathodes and quartz windows (two EMI 9750Q and one Philips XP 2020Q) and another with S11-type photocathode and glass window (FEU 85A) were tested down to −160 °C with a pulsed light source, both in the visible region and at the xenon scintillation wavelength in the vacuum ultraviolet. For the visible range, the results obtained with bialkali photomultipliers display a sharp drop of response at about −100 °C, depending o...

Compact, high-resolution, gamma ray imaging for scintimammography and other medical diagostic applications

Abstract: A high resolution gamma ray imaging device includes an aluminum housing, a lead screen collimator at an opened end of the housing, a crystal scintillator array mounted behind the lead screen collimator, a foam layer between the lead screen collimator and the crystal scintillator array, a photomultiplier window coupled to the crystal with optical coupling grease, a photomultiplier having a dynode chain body and a base voltage divider with anodes, anode wire amplifiers each connected to four anodes and a multi pin connector having pin connections to each anode wire amplifier. In one embodiment the crystal scintillator array includes a yttrium aluminum perovskite (YAP) crystal array. In an alternate embodiment, the crystal scintillator array includes a gadolinium oxyorthosilicate (GSO) crystal array.

Night vision device, image intensifier and photomultiplier tube, transfer-electron photocathode for such, and method of making

Abstract: A night vision device includes an image intensifier tube having a photocathode responsive to light in the wavelength range extending from about 1 μm to about 2 μm. The photocathode releases photoelectrons in response to photons of light in this wavelength range. A photomultiplier tube includes such a photocathode to provide an image in response to light of such a wavelength. A method of making such a photocathode is set out.

Characterization of a new multianode PMT for optical fiber readout at low-level light intensity

Abstract: We have characterized the new Hamamatsu R5900-L16 multianode photomultiplier with regard to its suitability for charge division position-sensitive readout with just two analog channels for each 16-anode PMT. Because of the low capacitance of the anode structure of the PMT, we obtain an output pulse width of less than 20 ns in response to narrow LED input pulses. We were able to obtain position-sensitive readout of light pulses corresponding to a single photoelectron with a spatial width of less than 1 mm FWHM for a collimated light source and of about 2 mm FWHM for a single fiber. Combined with the good single photoelectron peak for the R5900-L16, this provides excellent performance at very low-level light intensity. We discuss application of this device to the precise determination of gamma-ray interaction position within thin crystal scintillators.

Investigation of a new readout scheme for high resolution scintillation crystal arrays using photodiodes

Abstract: We are exploring the possibility of using PIN photodiodes to readout the scintillation crystals used in positron emission tomography (PET) detector designs. Semiconductor photodetectors typically have a lower signal to noise ratio than photomultiplier tubes (PMTs). However, they have the advantage of compactness, and, thus, scintillation crystal readout schemes not available to PMTs because of their size and geometry limitations, are readily available to photodiodes. With current PET detector designs, only a small fraction of the available scintillation light, created from 511 keV gamma ray interactions within the crystal, is collected. Scintillation light collection studies were performed for several crystal geometries and surface treatments using both simulations and measurements. In this report, we present a feasible photodiode readout scheme that allows greater than 90% of the available scintillation light created in either BGO or LSO scintillation crystals to be collected by the photodetector. This improvement in light collection with the photodiode readout somewhat compensates for its lower inherent signal to noise ratios and makes it feasible for use in PET detectors. A coincident timing spectrum resolution of 9.4 ns FWHM was measured for 511 keV interactions with one LSO crystal coupled to a photodiode, the other to a PMT.

An improved model for the energy resolution of multicrystal encoding detectors for PET

Abstract: Recently, we have shown that the program DETECT provides a realistic platform to model the performances of scintillation counters with geometries as involved as that of the EXACT HR PLUS, a state-of-the-art position and energy encoding EGO detector manufactured by Siemens-CTI for positron emission tomography (PET). In this paper we present the results of new simulations of this block's performances, updated to include the nonproportionality of the scintillation response of EGO and the statistical noise from photoelectron amplification in photomultiplier tubes (PMT's). The updated model accounts for the crystal-dependent energy resolutions observed with 511-keV photons in the detector with excellent accuracy. Measured and simulated resolutions are shown to agree within -1 to 4%, with an average absolute difference of 1% over the entire block. The impact of the nonproportional scintillation response of EGO on the energy resolution is shown to be relatively small compared to that of the amplification noise in the four PMT's reading out the block.

Novel hybrid imaging modalities

Abstract: The purpose of this paper is to present the engineering principles of a cost-effective and efficient positron emission tomography (PET) detector operating on novel hybrid principles. The novelty of the proposed technology, which can be considered a low-cost alternative to the photomultiplier tube, consists of a BaF2 crystal coupled to coupled to an ultra low-pressure noble-gas filled tube, which operates under photoionization of excited states, in the prebreakdown regime. The design detector principles, the first Townsend coefficient, and the gas multiplication factor of the hybrid microstrip detector have been studied. The results of this study indicate that an adequate gas multiplication process can be achieved with a Xe filled gas detector operating at low gas pressures. Also, low-pressure gas-filled detectors have the advantages of being themselves insensitive to radiation, ensuring that only the light from the scintillator is detected in a high-energy radiation environment.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.