Channel Photomultiplier Research Articles

A hydroxyl radical detection system using gas expansion and fast gating laser-induced fluorescence techniques

An OH radical measurement instrument based on Fluorescence Assay by Gas Expansion (FAGE) has been developed in our laboratory. Ambient air is introduced into a low-pressure fluorescence cell through a pinhole aperture and irradiated by a dye laser at a high repetition rate of 8.5kHz. The OH radical is both excited and detected at 308nm using A-X(0,0) band. To satisfy the high efficiency needs of fluorescence collection and detection, a 4-lens optical system and a self-designed gated photomultiplier (PMT) is used, and gating is actualized by switching the voltage applied on the PMT dynodes. A micro channel photomultiplier (MCP) is also prepared for fluorescence detection. Then the weak signal is accumulated by a photon counter in a specific timing. The OH radical excitation spectrum range in the wavelength of 307.82–308.2nm is detected and the excited line for OH detection is determined to be Q1(2) line. The calibration of the FAGE system is researched by using simultaneous photolysis of H2O and O2. The minimum detection limit of the instrument using gated PMT is determined to be 9.4×105molecules/cm3, and the sensitivity is 9.5×10−7cps/(OH·cm−3), with a signal-to-noise ratio of 2 and an integration time of 60sec, while OH detection limit and the detection sensitivity using MCP is calculated to be 1.6×105molecules/cm3 and 2.3×10−6cps/(OH·cm−3). The laboratory OH radical measurement is carried out and results show that the proposed system can be used for atmospheric OH radical measurement.

Gas discharge processes in metal channel and standard photomultiplier tubes

The effect of the potential difference at the focusing chamber electrodes of XP2020, FEU-85, FEU-87, and FEU-93 photomultiplier tubes on the intensity of afterpulses resulting from gas discharge processes is investigated. The time distributions of afterpulses in H6780 and R7600U-200 metal channel photomultiplier tubes are also analyzed.

Timing properties of phosphor-coated polished LSO crystals

This study investigates a time-of-flight (TOF)–depth-of-interaction (DOI) detector design for positron emission tomography (PET), based on phosphor-coated lutetium oxyorthosilicate (LSO) scintillator crystals coupled to fast single channel photomultiplier tubes. Interaction of the scintillation light with the phosphor coating changes the pulse shape in a depth-dependent manner. 3 × 3 × 10 mm3 LSO scintillation crystals with polished surfaces were characterized, with and without phosphor coating, to assess DOI capability and timing properties. Two different phosphor coating geometries were studied: coating of the top surface of the crystal, and the top plus half of the crystal sides. There was negligible depth dependency in the decay time when coating only the top surface, however there was a ∼10 ns difference in end-to-end decay time when coating the top plus half of the crystal sides, sufficient to support the use of three DOI bins (3.3 mm DOI bin width). The rise time of the half-coated phosphor crystal was slightly faster at all depths, compared to uncoated crystals, however the signal amplitude was lower. Phosphor coating resulted in depth-dependent photopeak positions with an energy resolution of 13.7%, at a depth of 1 mm, and 15.3%, at a depth of 9 mm, for the half-coated crystal. Uncoated LSO crystals showed no change in photopeak position as a function of depth, with an energy resolution of 10.4%. The head-on coincidence timing resolution (CTR) of two uncoated LSO crystals was 287 ps using constant fraction discrimination for time pick-off. With phosphor coating, the CTR of the top-coated crystal was 314 ps, compared to 384 ps for the half-coated crystal. We demonstrate that the trade-off between timing resolution and DOI resolution can be controlled by the phosphor coating geometry. Here we present preliminary results demonstrating that good DOI resolution can be achieved with only a modest 26% degradation in CTR.

Development of multi-channel Doppler spectroscopic measurement system using 8 × 8 multianode photomultiplier tube assembly

Using an 8 × 8 channel photomultiplier tube assembly and a single Czerny-Turner monochromator, we have developed a novel Doppler spectroscopic system which can measure the time evolutions of spectral distribution of plasma emission from eight different lines of sight simultaneously. An optical lens system is employed to couple the output of the monochromator with the detector assembly, resulting in small cross-talks less than 5% in spatial distribution together with large magnification of up to 50 in wavelength direction. The suggested system yields cost-effective polychromatic measurements of eight spatial channels with uniform optical and electrical characteristics.

High resolution ion Doppler spectroscopy at Prairie View Rotamak

A fast ion Doppler spectroscopy (IDS) diagnostic system is installed on the Prairie View Rotamak to measure ion temperature and plasma flow. The diagnostic employs a single channel photomultiplier tube and a Jarrell-Ash 50 monochromator with a diffraction grating line density of 1180 lines/mm, which allows for first order spectra of 200-600 nm. The motorized gear of the monochromator allows spectral resolution of 0.01 nm. Equal IDS measurements are observed for various impurity emission lines of which carbon lines exhibit stronger intensities. Furthermore, the diagnostics is examined in an experiment where plasma experiences sudden disruption and quick recovery. In this case, the IDS measurements show ~130% increase in ion temperature. Flow measurements are shown to be consistent with plasma rotation.

Participation in the CCRI(II)-K2.H-3 comparison and study of the new TDCR-LS counter with 6 CPMs

The "conventional" TDCR system was used for standardization of the tritiated water in the frame of the international comparison organized by CCRI(II). The prototype of the new TDCR realized at LNHB with three CPMs (Ivan et al., 2008) was improved by constructing at IFIN-HH, a system containing six channel photomultiplier tubes arranged symmetrically in a new optical chamber. The system was tested by measuring various pure beta emitters and for comparative measurements of tritiated water for validation studies.

A time-gating scintillation detector for the measurement of laser-induced fast neutrons

A time-gating scintillation detector, in which a fast high voltage switch is used for gating a channel photomultiplier, was developed for a measurement of laser-induced fast neutrons. The x rays generated from the intense femtosecond laser and the solid target interactions were suppressed selectively and a time-of-flight signal of a laser-generated fast neutron was measured effectively. The detector was used successfully to measure the neutron yield of a femtosecond, deuterated, polystyrene plasma.

A new TDCR-LS Counter using Channel photomultiplier tubes

A new Triple to Double Coincidence Ratio (TDCR) liquid scintillation (LS) counter using recently available photodetectors, the Channel photomultiplier (CPM) tubes, was constructed and tested in the framework of a scientific cooperation between IFIN-HH and LNHB. The prototype LS counter uses 3CPM tubes arranged symmetrically in an optical chamber around a standard LS vial. The behavior of the prototype was first evaluated with a light emitting diode (LED) light pulser. The counter was then compared against a TDCR counter using conventional photomultiplier tubes, by measuring 55Fe, 3H, 63Ni and 90Sr/ 90Y LS sources prepared in commercial liquid scintillation cocktails. Although the observed detection efficiency was significantly lower than the one achieved with the traditional counter, we found a remarkable agreement on the activity determination using the two counters. Details on the prototype and the measurement results obtained are discussed in this paper.

Practical time‐gated luminescence flow cytometry. II: Experimental evaluation using UV LED excitation

In the previous article [Part 1 (8)], we have modelled alternative approaches to design of practical time-gated luminescence (TGL) flow cytometry and examined the feasibility of employing a UV LED as the excitation source for the gated detection of europium dye labelled target in rapid flow stream. The continuous flow-section approach is well suited for rare-event cell counting in applications with a large number of nontarget autofluorescent particles. This article presents details of construction, operation and evaluation of a TGL flow cytometer using a UV LED excitation and a gated high-gain channel photomultiplier tube (CPMT) for detection. The compact prototype TGL flow cytometer was constructed and optimised to operate at a TGL cycle rate of 6 kHz, with each cycle consisting of 100 micros LED pulsed excitation and approximately 60 micros delay-gated detection. The performance of the TGL flow cytometer was evaluated by enumerating 5.7 microm Eu(3+) luminescence beads (having comparable intensity to europium-chelate-labeled Giardia cysts) in both autofluorescence-rich environmental water concentrates and Sulforhodamine 101 (S101) solutions (broadband red fluorescence covering the spectral band of target signals), respectively. The prototype TGL flow cytometer was able to distinguish the target beads, and a maximum signal to background ratio of 38:1 was observed. Neither the environmental water concentrates nor S101 solution contributed to the background in the TGL detection phase. The counting efficiency of the TGL flow cytometer was typically >93% of values determined using conventional counting methods.

A new principle photosynthesis capacity biosensor based on quantitative measurement of delayed fluorescence in vivo

Delayed fluorescence (DF) is an excellent marker for evaluating plant photosynthesis. Compared with common methods for measuring the photosynthesis rate based on consumption of CO2, DF technique can quantify the plant photosynthesis capacity more accurately and faster under its physiological status with less interference from the environment. We previously reported a method for measuring photosynthesis using DF of chloroplast [Wang, C.L., Xing, D., Chen, Q., 2004. Biosens. Bioelectron. 20, 454–459]. In the study, a novel fast and portable photosynthesis capacity biosensor system was developed, which was composed of light-emitting diode lattice as excitation light source, Channel Photomultiplier DC-Module to achieve DF, single-chip microcomputer as control center, hermetic dark sample chamber, battery power supply and CO2, humidity and temperature controller. Compared with our previous work, the system was portable and can directly measure plant photosynthesis capacity in vivo in less than 10s. A database in the software to carry out data acquisition and processing was developed to translate maximal DF intensity to net photosynthesis rate (Pn). In addition, local-control and remote-control mode can be chosen in the system. To demonstrate the utility of the system, it was applied to evaluate maximum Pn of four different plant species samples (Queen Rape Myrtle (var. rubra), soybean (Lu Hei No. 1), maize (Jin Dan No. 39) and rice (Jing Dao No. 21)) in field. The results were compared with that using commercial photosynthesis system LI-6400 and the uncertainty was less than ±5%. The new principle of photosynthesis measurement is a challenge and breakthrough to conventional method of gas exchange and may be a potential technique of next generation photosynthesis measurement.

Mass characterization of MaPMT tubes for the LHCb scintillator pad detector

The final choice as the photomultiplier solution for both the LHCb Pre-Shower (PS) and the Scintillator Pad Detector (SPD) are the R7600-00-M64MOD Hamamatsu 64 channel photomultiplier tubes (MaPMT). A total of 220 units have been purchased to the manufacturer and around 100 units, the part corresponding to the SPD, have been characterized at the photon detection test bench facility in the University of Barcelona (UB) high energy physics group laboratory. There, the crucial features of the tubes such as linearity, gain, channel cross-talk and anode uniformity of response have been measured to ensure the compliance with the specifications agreed with the manufacturer.

Gating a channel photomultiplier with a fast high-voltage switch: reduction of afterpulse rates in a laser-induced fluorescence instrument for measurement of atmospheric OH radical concentrations

By employing a commercially available high-voltage switch in a time-gating circuit to drive a channel photomultiplier (CPM), the afterpulse rates are significantly reduced in the time window to collect fluorescence >200 ns after the pulsed laser excitation. The CPM, kept deactivated under normal conditions (normally off), is turned on immediately after the passage of the laser pulse by shifting the voltage applied to the photocathode by 150 V to collect the fluorescence. When the detection system is used as part of a laser-induced fluorescence instrument to measure atmospheric OH radicals with the photon-counting method, the background signal is reduced by more than a factor of 10 as compared with our previous case where a conventional dynode-gated photomultiplier tube (PMT) is used, while the sensitivity toward the fluorescence is almost unchanged. A detection limit as low as 2 x 10(5) radicals cm-3 or 0.008 parts per trillion by volume is achieved for OH, with an integration time of 1 min and a signal-to-noise ratio of 2, enabling sensitive detection of the important radical in the atmosphere. This system is a superior choice with higher sensitivity and cost effectiveness as compared with the gated PMITs utilizing a microchannel plate as an electron multiplier, and could also be used effectively in light detection and ranging (lidar) instruments, where a delayed scattering signal would be efficiently discriminated from afterpulses.

Modified branching ratio method for absolute intensity calibration in VUV spectroscopy

A new modified branching ratio (MBR) method for the absolute intensity calibration of a vacuum ultraviolet (VUV) spectrometer is presented. The spectrometer is equipped with a multichannel detector, consisting of an open microchannel plate coupled to a charge-coupled device (CCD), or with a single channel photomultiplier. This technique extends the number of calibration points available from those provided by the branching ratio (BR) calibration technique. The MBR method is a variation of the conventional BR method, where we relax the condition that the two spectral emissions, in the visible and VUV spectra, come from the same excited level, to include transitions from different sublevels of the same energy level. However, a critical study of the statistical equilibrium of sublevels from the same ion energy level was necessary. As a result, we have more than doubled the number of calibration points for our spectrometer used in tokamak plasma diagnostics. The appropriate identification of new spectral line pairs for absolute calibration here presented opens the path for future works in other devices with similar plasma conditions or impurities content.

Microchip Separations in Reduced-Gravity and Hypergravity Environments

Microfabricated fluidics technology, e.g., lab-on-a-chip devices, offers many attractive features for performing chemistry and biochemistry on space-based platforms. We have constructed a portable, battery-operated microfluidic platform that was tested under reduced gravity and hypergravity conditions that would be experienced in space flight and launch. This device consisted of a microchip, microchip holder, two 0-8-kV high-voltage power supplies, a high-voltage switch, a solid-state diode-pumped green laser, an optical train, a channel photomultiplier, and an inertial mass measurement unit all under the control of a laptop computer and powered by 10 D-cell alkaline batteries. The unit was tested on NASA's reduced gravity research aircraft at gravity levels that are relevant to NASA's intended use of bioreporter-based microchips for environmental monitoring of space and planetary environments on manned and unmanned spacecraft. Over the course of two flights, 834 fast electrophoretic separations of four amino acids were performed under a variety of gravitational environments including zero-g, Martian-g, lunar-g, and approximately 1.8-g. All separations were performed in less than 12 s and automatically analyzed. After correction with an internal migration standard, the migration time reproducibilities were all <1% relative standard deviation.

Upgrade of a Raman Spectrometer

Improvement of a conventional JEOL Raman spectrometer with a single channel photo multiplier detector is described. New optical components [fibers, mirror, lens, and charge coupled device detector (CCD)] have been chosen to design a high quality and easy‐to‐use instrument. Tests have shown that with this modified spectrometer, Raman spectra can be acquired of a quality comparable to the spectra obtained previously, but the time needed to obtain a spectrum is markedly reduced. Selected test spectra and a simple calibration procedure to obtain the wavenumber values from the band CCD pixel position are presented.

Proportional light in a dual-phase xenon chamber

A dual-phase xenon chamber was tested to measure the yield of electrons extracted from the liquid to the gas and their subsequent amplification via proportional light. The light yield was studied as a function of electric field and gas pressure. A UV-sensitive compact metal channel photomultiplier tube, placed in the gas above the liquid xenon, was used for these measurements. An electron lifetime of at least 1.5 ms was inferred from a measurement of the ionization signal, triggered by the primary scintillation light, with the same chamber operated in single phase.

Measurements of performance of a pixel-type two-dimensional position sensitive Li-glass neutron detector

We have developed a pixel-type two-dimensional position sensitive Li-glass neutron detector for high rate application, which would be useable for time-of-flight radiography, namely transmission spectroscopy. The pieces of Li-glass were attached directly to a 8×8 channel photo multiplier. We measured its performance at KEK and Hokkaido University. The count rate of this detector was found to be about 8.3 Mcps/cm 2 (240 Kcps per pixel). The efficiency of the detector corrected for the effective detection area is 100% over 9 Å and 95% at 3 Å. The difference in the count rate of each pixel was very small, less than 2%.

Optimization of multi-photon event discrimination levels using Poisson statistics

In applications where random multi-photon events must be distinguishable from the background, detection of the signals must be based on either analog current measurement or photon counting and multi-level discrimination of single and multi-photon events. In this paper a novel method for optimizing photomultiplier (PMT) pulse discrimination levels in single- and multi-photon counting is demonstrated. This calibration method is based on detection of photon events in coincidence to short laser pulses. The procedure takes advantage of Poisson statistics of single- and mult-iphoton signals and it is applicable to automatic calibration of photon counting devices on production line. Results obtained with a channel photomultiplier (CPM) are shown. By use of three parallel discriminators and setting the discriminator levels according to the described method resulted in a linear response over wide range of random single- and multi-photon signals.

Ion Doppler Spectroscopic Measurement with a Multi-channel PMT on Spheromak Plasmas

An ion Doppler spectrometer (IDS) using a compact 16 channel photomultiplier tube (PMT) has been developed and used to measure ion temperature and toroidal rotation speed on SSPX gun-spheromaks. Doppler broadening of OV spectral line shows higher ion temperature (-500 eV) as compared to the electron temperature, which indicates anomalous ion heating due to MHD relaxation. It has been also found that the plasma rotates with a speed of 60 km/s in the direction of E×B.

A channel photomultiplier with a scintillator faceplate

A channel photomultiplier has been constructed using a YAP(Ce) scintillator as an entrance window. First results of performance measurements show a significant improvement of the photoelectron yield over the same scintillator coupled to conventional borosilicate-glass windows.