Showing papers on "Photomultiplier published in 2008"

Performance of 1- ${\hbox {mm}}^{2}$ Silicon Photomultiplier

Abstract: A silicon photomultiplier (SPM) is a large area detector consisting of a parallel array of photon counting microcells. Each microcell consists of a Geiger Mode photodiode with an integrated quenching element. Each microcell is then connected to a common output. The microcells have a uniform gain of up to 10 and provide an identical charge output signal for each photon detected. Under illumination the summed output of the detector is proportional to the number of Geiger pulses and hence proportional to the incident photon flux. This combination gives extremely high performance comparable to that of a conventional photomultiplier tube (PMT). We report on the characterization of two different 1 mm2 SPM detector designs with 620 and 920 microcells at room temperature (20 deg) and down to . We assess detection efficiency, breakdown voltage, gain, dark rate, crosstalk, timing jitter and dynamic range. The SPM detector operates over the visible region of the spectrum, characterized here from 400 to 800 nm. The peak photon detection efficiency of 15% occurs at 500 nm with a cooled () dark rate of 600 at a bias voltage of 31 V. In a test for positron emission tomography (PET), an energy resolution of 25% was recorded for the detection of 511 keV gamma radiation using 1 mm1 mm15 mm LYSO scintillator crystal. The SPM has many applications such as medical imaging, microscopy, high-energy physics, and homeland security.

FADC signal reconstruction for the MAGIC telescope

Abstract: Until April 2007 the Major Atmospheric Gamma ray Imaging Cherenkov (MAGIC) telescope used a 300 MSamples/s flash analog-to-digital converter (FADC) system to sample the shaped photomultiplier tube (PMT) signals produced by the captured Cherenkov photons of air showers. Different algorithms to reconstruct the signal from the read-out samples (extractors) have been implemented and are described and compared. Criteria based on the obtained charge and time resolution/bias are defined and used to judge the different extractors, by applying them to calibration, cosmic and pedestal signals. The achievable charge and time resolution have been derived as functions of the number of incident photoelectrons. (C) 2008 Elsevier B.V. All rights reserved.

Large-area low-jitter silicon single photon avalanche diodes

Abstract: Single photon counting (SPC) and time correlated single photon counting (TCSPC) techniques have been developed in the past four decades relying on photomultiplier tubes (PMT), but interesting alternatives are nowadays provided by solid-state single photon detectors. In particular, silicon Single Photon Avalanche Diodes (SPAD) fabricated in planar technology join the typical advantages of microelectronic devices (small size, ruggedness, low operating voltage and low power dissipation, etc.) with remarkable basic performance, such as high photon detection efficiency over a broad spectral range up to 1 μm wavelength, low dark count rate and photon timing jitter of a few tens of picoseconds. In recent years detector modules employing planar SPAD devices with diameter up to 50 µm have become commercially available. SPADs with larger active areas would greatly simplify the design of optical coupling systems, thus making these devices more competitive in a broader range of applications. By exploiting an improved SPAD technology, we have fabricated planar devices with diameter of 200 μm having low dark count rate (1500 c/s typical @ -25 °C). A photon timing jitter of 35 ps FWHM is obtained at room temperature by using a special pulse pick-up network for processing the avalanche current. The state-of-the-art of large-area SPADs will be reviewed and prospects of further progress will be discussed pointing out the challenging issues that must be faced in the design and technology of SPAD devices and associated quenching and timing circuits.

Characterization of a Novel 100-Channel Silicon Photomultiplier—Part I: Noise

Abstract: In this paper, we present the results of the first noise characterization performed on our novel 100-channel silicon photomultiplier. We have improved our previous single-photon avalanche photodiode technology in order to set up a working device with outstanding features in terms of single-photon resolving power up to R = 45, timing resolution down to 100 ps, and photon-detection efficiency of 14% at 420 nm. Tests were performed, and features were measured, as a function of the bias voltage and of the incident photon flux. A dedicated data-analysis procedure was developed that allows one to extract at once the relevant parameters and quantify the noise.

Cross-talk suppressed multi-anode MCP-PMT

Abstract: We have developed a 4-channel multi-anode MCP-PMT, SL10, which exhibits good performance of the transit time spread, σ TTS ≃ 30 ps for single photons with a gain of ∼ 10 6 and a peak quantum efficiency of 20 % under a magnetic field of ⩽ 1.5 T . The cross-talk among anodes has been extensively studied. We have taken two measures to suppress it: one is to configure the SL10 to an effectively independent four small pieces of MCP-PMT's by segmenting an electrode of the second MCP-layer; the other is to use a constant-fraction discriminator. A remarkable improvement has been achieved.

High brightness and high polarization electron source using transmission photocathode with GaAs-GaAsP superlattice layers

Abstract: In order to produce a high brightness and high spin polarization electron beam, a pointlike emission mechanism is required for the photocathode of a GaAs polarized electron source. For this purpose, the laser spot size on the photocathode must be minimized, which is realized by changing the direction of the injection laser light from the front side to the back side of the photocathode. Based on this concept, a 20kV gun was constructed with a transmission photocathode including an active layer of a GaAs–GaAsP superlattice layer. This system produces a laser spot diameter as small as 1.3μm for 760–810nm laser wavelength. The brightness of the polarized electron beam was ∼2.0×107Acm−2sr−1, which corresponds to a reduced brightness of ∼1.0×107Am−2sr−1V−1. The peak polarization of 77% was achieved up to now. A charge density lifetime of 1.8×108Ccm−2 was observed for an extracted current of 3μA.

Boron-10 Loaded BC523A Liquid Scintillator for Neutron Detection in the Border Monitoring

Abstract: A BC523A liquid scintillator loaded with boron-10 was tested as a detector for both fast and thermal neutrons. A pulse shape discrimination (PSD) method based on a zero-crossing principle was applied to distinguish between neutron and gamma radiation. High quantum efficiency Photonis XP5500B photomultiplier was used to enhance light detection from the scintillator. This allowed a good registration of the energy spectrum of neutron capture events on boron-10, corresponding to about 60 keV gamma-rays. The applied PSD method proved to be useful for n/gamma discrimination. A good resolving power of the method was achieved even without gating on neutron capture events. A comparison with a standard BC501A liquid scintillator was done to evaluate thermal neutrons detection efficiency in BC523A.

Enhanced red and near infrared detection in flow cytometry using avalanche photodiodes

Abstract: Polychromatic flow cytometry enables detailed identification of cell phenotype using multiple fluorescent parameters. The photomultiplier tubes (PMTs) used to detect fluorescence in current instruments limit the sensitivity in the long wavelength spectral range. We demonstrate the flow cytometric applications of silicon avalanche photodiodes (APDs), which have improved red sensitivity and a working fluorescence detection range beyond 1,000 nm. A comparison of the wavelength-dependent performance of the APD and PMT was carried out using pulsed light-emitting diode sources, calibrated test beads, and biological samples. A breadboard flow cytometer test bench was constructed to compare the performance of PMTs and APD detectors. The APD used an additional amplifier stage to match the internal gain of the PMT. The resolution of the APD and PMT was compared for flow cytometry applications using a pulsed light-emitting diode source over the 500-1060 nm spectral range. These measurements showed the relative changes in the signal-to-noise performance of the APD and PMT over a broad spectral range. Both the APD and PMTs were used to measure the signal-to-noise response for a set of six peak calibration beads over the 530-800 nm wavelength range. CD4-positive cells labeled with antibody-conjugated phycoerythrin or 800 nm quantum dots were identified by simultaneous detection using the APD and the PMT. The ratios of the intensities of the CD4- and CD4+ populations were found to be similar for both detectors in the visible wavelengths, but only the APD was able to separate these populations at wavelengths above 800 nm. These measurements illustrate the differences in APD and PMT performance at different wavelengths and signal intensity levels. While the APD and PMT show similar signal-to-noise performance in the visible spectral range, the dark noise of the APD detector reduces the sensitivity at low signal levels. At wavelengths longer than 650 nm, the high quantum efficiency of the APD contributes to better signal-to-noise performance. The APD detector provides enhanced performance in the long wavelength region and may be used to extend the working range of the flow cytometer beyond 1,000 nm.

Afterpulse timing and rate investigation of three different Hamamatsu Photomultiplier Tubes

Abstract: We present the results of the tests performed on 90 photomultiplier tubes (PMT) to characterize their afterpulses. Three different types of H amamatsu PMTs (R7525, R6427, and R1398) were studied for their afterpulse rates and timings at different incident light intensities and gain values, at the University of Iowa PMT test station. Afterpulse rates show slight increase with the PMT gain, but there is almost no dependence on incident light intensity. Three specific time delays are determined for the afterpulses, and their indivi dual rate contributions are characterized. The results from manufacturer's independent tests on R7525 PMTs are reported, as well. The possible effects of these afterpulses on the future hadron c ollider experiments are also discussed.

Quantum Detection Efficiency in Geiger Mode Avalanche Photodiodes

Abstract: The fabrication of silicon shallow junction photodiodes is a relevant topic for the detection of blue and near ultraviolet weak photon fluxes. In this paper we present a simple model to calculate the quantum detection efficiency (QDE) of a Geiger mode avalanche photodiode (GMAP) as a function of the dead layer thickness above the junction depletion layer. A comparison between calculated and experimental data is also presented. Moreover, by using the same model, an analysis of the QDE at 420 nm wavelength of conventional GMAPs based on shallow N+-P and P+-N junctions is given.

Study of LaBr $_{3}$ Crystals Coupled to Photomultipliers and Avalanche Photodiodes

Abstract: The performance of several BrilLanCe LaBr3 crystals that range in size from Oslash 6 times 6 mm2 up to Oslash 38 times 38 mm2 coupled to XP5212 and R6231MOD photomultipliers were studied, and in the case of the small crystals, the crystals were also coupled to large area avalanche photodiodes (LAAPD) of Advanced Photonix, Inc. First, the performance of several photomultipliers from Photonis and Hamamatsu with LaBr3 were compared to select the best one, not affecting energy resolution, besides the photoelectron statistics. The light output and energy resolution for 662 keV gamma rays from137 Cs source were measured for all crystals. Moreover, for some crystals, the non-proportionality of the light yield and energy resolution versus gamma ray energy were measured and the intrinsic resolution of the crystals was calculated. For the smallest crystals of Oslash 6 times 6 mm2 further comparative tests with LAAPD were carried out.

Gamma ray spectroscopy at high energy and high time resolution at JET.

Abstract: In fusion plasmas gamma ray emission is caused by reactions of fast particles, such as fusion alpha particles, with impurities. Gamma ray spectroscopy at JET has provided valuable diagnostic information on fast fuel as well as fusion product ions. Improvements of these measurements are needed to fully exploit the flux increase provided by future high power experiments at JET and ITER. Limiting aspects are, for instance, the count rate capability due to a high neutron/gamma background combined with slow detector response and a modest energy resolution due to the low light yield of the scintillators. This paper describes the solutions developed for achieving higher energy resolution, signal to background, and time resolution. The detector design is described based on the new BrLa3 scintillator crystal. The paper will focus on hardware development, including a photomultiplier tube capable of stable operation at counting rate as high as 1MHz, the magnetic shielding, and the fast digital data acquisition system.

Luminescence Emission Properties of $({\rm Lu},{\rm Y})_{2}{\rm SiO}_{5}$ :Ce (LYSO:Ce) and $({\rm Lu},{\rm Y}){\rm AlO}_{3}$ :Ce (LuYAP:Ce) Single Crystal Scintillators Under Medical Imaging Conditions

Abstract: LYSO:Ce and LuYAP:Ce are single crystal non-hygroscopic scintillators of high density, high light yield and short decay time, which have been successfully used in small animal PET imagers. In the present study, the luminescence emission properties of (Lu0.9, Y0.1)2SiO5:Ce (LYSO:Ce) and (Lu0.7, Y0.3)AIO3:Ce (LuYAP:Ce) crystals were investigated for use in X-ray medical imaging. Both crystals had dimensions of 2 times 2 times 8 mm3, with all surfaces polished. Evaluation was performed by determining the X-ray luminescence efficiency (XLE) (emitted light energy flux over incident X-ray energy flux) and the detector optical gain (DOG) (emitted light photons per incident x-ray photon) in a wide range of X-ray energies employed in mammography (22-49 kVp) and in general X-ray imaging (50-140 kVp). Measurements were performed using an experimental set-up based on a photomultiplier coupled to an integration sphere. The emission spectrum under X-ray excitation was measured using an optical grating monochromator to determine the spectral compatibility to various optical photon detectors incorporated in medical imaging detectors. Optical characteristics such as transmission and absorption spectra were investigated in addition to the scintillation properties. The light emission performance of the two scintillation materials studied was found adequately high for X-ray imaging.

Avalanche multiplication in amorphous selenium and its utilization in imaging

Abstract: Amorphous selenium (a-Se) is a well known photoconductor that is currently used in X-ray image detectors and HARP video tubes Recent advances have made it practical to operate a-Se at extremely high electric fields F , where avalanche multiplication occurs At sufficiently high fields, the effective quantum efficiency ( η ∗ ) (or the overall yield) of the photoconductor can be increased several orders of magnitude above unity and renders avalanche a-Se photoconductors a prospective alternative to vacuum photomultiplier tubes (PMTs) and silicon avalanche photodiodes (APDs) In this work we report our study of η ∗ and charge transport for a-Se avalanche photoconductors with different photoconductive layer thicknesses in wide range of F Our study shows that a-Se is able to produce a gain of ∼1000 with a rise time of ∼1 ns, both of which clearly point to the potential (or realized) use of this photoconductor in a variety of imaging applications Furthermore, our work supports the validity of the so-called modified Lucky drift model to explain the nature of impact ionization and avalanche in this material

Optimized photocathode for spin-polarized electron sources

Abstract: Photocathode for highly polarized electron emission has been developed, fabricated, and studied. The photocathode is based on short-period strained AlInGaAs∕AlGaAs superlattice grown by molecular beam epitaxy. Deformation of AlInGaAs quantum well results in 87meV energy splitting between heavy hole and light hole minibands. Electron emission from the developed photocathode demonstrates maximal polarization of 92% with quantum efficiency of 0.85% at room temperature.

Wavelength shifters for water Cherenkov detectors

Abstract: The light yield of a water-based Cherenkov detector can be significantly improved by adding a wavelength shifter (WLS). WLS molecules absorb ultraviolet photons and re-emit them at longer wavelengths where typical photomultiplier tubes are more sensitive. In this study, several WLS compounds are tested for possible deployment in the Sudbury Neutrino Observatory (SNO). Test results on optical properties and chemical compatibility for a few WLS candidates are reported; together with timing and gain measurements. A Monte Carlo simulation of the SNO detector response is used to estimate the total light gain with WLS. Finally, a cosmic ray Cherenkov detector was built to investigate the optical properties of WLS.

Single-photon avalanche photodiodes with integrated quenching resistor

Abstract: In this paper we present the results of the first electrical and optical characterization performed on STMicroelectronics new photosensor technology based on silicon single-photon avalanche photodiodes (SPAD). On the prospective of the design and the manufacturing of large-area silicon photomultipliers to be used as photodetectors for nuclear medicine imaging applications, we have modified our previous SPAD technology by means of the integration of a high-value quenching resistor to the photodiode. Moreover, an appropriate antireflective coating layer and the reduction of the quasi-neutral region thickness above the thin junction depletion layer have been introduced in the process flow of the device to enhance its spectral response in blue and near ultraviolet wavelength ranges. High gain, low leakage currents, low dark noise, very good quantum detection efficiency in blue–near UV ranges and a good linearity of the photodiode response to the incident luminous flux are the main characterization results.

Thermal and Electrical Characterization of Silicon Photomultiplier

Abstract: Detection of low levels of light is one of the key aspects in medical and space applications. Silicon photomultiplier, a novel type of avalanche photodetector which operates in Geiger mode, shows promising results and offer superior design options. The performance characteristics of the SiPM realized in FBK-irst are studied and presented in this paper. The leakage current, dark rate and internal gain are characterized as a function of temperature. The investigation has been carried out in the framework of the DASiPM Collaboration and the INFN/FBK-irst MEMS project.

High spatial and energy resolution gamma imaging based on LaBr3(Ce) continuous crystals

Abstract: Recently scintillators with very high light yield and photodetectors with high quantum efficiency have been opening a new way to realize gamma cameras with superior performances based on continuous crystals. Pixilated imagers have a spatial resolution limited by pixel size, in contrast with continuous scintillation crystals, where spatial resolution is a statistical function depending on light distribution spread and on generated photoelectrons from scintillation light flash. Continuous LaBr 3 :Ce crystal, with a light yield almost two times higher than NaI:Tl ones and a lower intrinsic energy resolution, could be the best candidate to carry out a gamma imaging with sub-millimeter spatial resolution and very good energy resolution. Unfortunately standard Anger algorithm produces an intrinsic position non-linearity affecting spatial resolution for small size continuous crystal. In this work we propose a new method to calculate the position mean value by squaring the 2D collected charge distribution on a multi-anodes photomultiplier tube (MA-PMT). In this study we take into account four different detector configurations: three sample of LaBr 3 :Ce scintillation crystals, 49mm×49mm area, a couple of 4.0 with different surface treatment and a single 10 mm thick, with 3 mm glass window. Moreover a forth one with 5.0mm thickness which was integral assembled with an Hamamatsu H8500. We applied the new position algorithm to simulated data, obtained by Geant4 code and afterwards to the experimental data obtained scanning the different detectors with 0.4 mm O collimated Tc99m point source, at 1.5 mm step. The results obtained with the new algorithm show an improvement in position linearity and in spatial resolution of about a factor two. The best values in terms of spatial resolution were 0.9 mm, 1.1 mm and 1.8 mm for integral assembled, 4.0 mm thick and 10 mm thick LaBr 3 :Ce crystal respectively. These results demonstrate the potential of LaBr crystal for molecular imaging application and more in general for gamma ray imaging

The central pixel of the MAGIC telescope for optical observations

Abstract: The MAGIC telescope has been designed for the observation of Cherenkov light generated in Extensive Air Showers initiated by cosmic particles. However, its 17m diameter mirror and optical design makes the telescope suitable for direct optical observations as well. In this paper, we report about the development of a system based on the use of a dedicated photo-multiplier (PMT) for optical observations. This PMT is installed in the centre of the MAGIC camera (the so-called central pixel). An electro-to-optical system has been developed in order to transmit the PMT output signal by an optical fibre to the counting room, where it is digitized and stored for off-line analysis. The performance of the system using the optical pulsation of the Crab nebula as calibration source is presented. The time required for a 5 sigma detection of the Crab pulsar in the optical band is less than 20s. The central pixel will be mainly used to perform simultaneous observations of the Crab pulsar both in the optical and gamma-ray regimes. It will also allow for periodic testing of the precision of the MAGIC timing system using the Crab rotational optical pulses as a very precise timing reference. (c) 2008 Elsevier B.V. All rights reserved.

PESIC: An Integrated Front-End for PET Applications

Abstract: An ASIC front-end has been developed for multianode photomultiplier based nuclear imaging devices. Its architecture has been designed to improve resolution and decrease pile-up probability in positron emission tomography systems which employ continuous scintillator crystals. Analog computation elements are isolated from the photomultiplier by means of a current sensitive preamplifier stage. This allows digitally programmable adjustment of every anode gain, also providing better resolution in gamma event position calculation and a shorter front-end deadtime. The preamplifier stage also offers the possibility of using other types of photomultiplier devices such as SiPM. The ASIC architecture includes measurement of the depth of interaction of the gamma event based on the width of the light distribution in order to reduce parallax error and increase spatial resolution during image reconstruction stage. An output stage of transresistance amplifiers offer voltage output signals which may be introduced in the A/D conversion stage with no further processing.

A new high-gain vacuum photomultiplier based upon the amplification of a Geiger-mode p-n junction

Abstract: The future astroparticle experiments will study both energetic phenomena and extremely rare events from astrophysical sources. Since most of these families of experiments are carried out by using scintillation phenomena, Cherenkov or fluorescence radiation, the development of photosensitive detectors seems to be the right way to increase the experimental sensitivity. We therefore propose an innovative design for a modern, high gain, silicon-based Vacuum Silicon Photomultiplier Tube (VSiPMT), which combines three fully established and well-understood technologies: the manufacture of hemispherical vacuum tubes with the possibility of very large active areas, the photocathode glass deposition and the recent Geiger-mode avalanche silicon photodiode (G-APD) for which a mass production is today available. This new design, based on G-APD as the electron multiplier, allows overcoming the limits of the classical PMT dynode chain.

New Raman Spectrometer Using a Digital Micromirror Device and a Photomultiplier Tube Detector for Rapid On-Line Industrial Analysis. Part I: Description of the Prototype and Preliminary Results

Abstract: In this paper, a prototype of a new generation of Raman spectrometers, based on the use of a monochromator, a digital micromirror device as light modulator, and a photomultiplier tube as detector of the Raman light, is described. This spectrometer, containing no moving parts, is inexpensive, robust, and very precise. New in concept, this spectrometer makes it possible to record, in addition to classical Raman spectra, the intensity at several selected points of the spectrum and/or the total intensity in several selected intervals at the same time with great accuracy, thus giving new possibilities for analytical applications. Also, the work presented demonstrates the possibilities of this very simple prototype for rapid on-line industrial analysis, with an example of quantitative analysis of binary and ternary mixtures of xylene isomers. The precision obtained is satisfactory (errors of prediction ∼3% in 5–6 seconds per sample).

A comparison of avalanche photodiode and photomultiplier tube detectors for flow cytometry

Abstract: Commercial flow cytometers use photomultiplier tubes (PMTs) for fluorescence detection. These detectors have high linear gain and broad dynamic range, but have limited sensitivity in the red and near infrared spectral regions. We present a comparison of avalanche photodiodes (APDs) and PMTs as detectors in flow cytometry instruments, and demonstrate improved sensitivity and resolution in the red and near infrared spectral regions using the APD. The relative performance of the PMT and APD were evaluated by simultaneously measuring the mean fluorescence intensity and coefficient of variation for emission from light emitting diode pulses, flow cytometry test beads, and fluorescently labeled cells. The relative signal to noise performance of the APD and PMT was evaluated over the 500 nm to 1050 nm wavelength range using pulsed light emitting diode light sources. While APDs have higher quantum efficiency but lower internal gain than PMTs, with appropriate external amplification the APD has signal to noise response that is comparable to PMTs in the 500 nm to 650 nm range and improved response in the 650 nm to 850 nm range The data demonstrates that the APD had performance comparable to the PMT in the spectral region between 500 to 650 nm and improved performance in the range of 650 to 1000 nm, where the PMT performance is quite poor. CD4 positive lymphocyte populations were easily identified in normal human blood both by APD and PMT using phycoerythrin labeled antibodies. In contrast, only the APD detector could resolve CD4 positive populations using 800 nm Quantum dot labeled antibodies.

Silicon photomultiplier as a detector of Cherenkov photons

Abstract: A novel photon detector—i.e. the silicon photomultiplier—whose main advantage over conventional photomultiplier tubes is the operation in high magnetic fields, has been tested as a photon detector in a proximity focusing RICH with aerogel radiator. This type of RICH counter is proposed for the upgrade of the Belle detector at the KEK B-factory. Recently produced silicon photomultipliers show less noise and have larger size, which are important issues for a large area photon detector. We measured the single photon pulse height distribution, the timing resolution and the position sensitivity for different silicon photomultipliers (Hamamatsu MPPC HC025, HC050, and HC100). The silicon photomultipliers were then used to detect Cherenkov photons emitted by cosmic ray particles in a proximity focusing aerogel RICH. Various light guides were investigated in order to increase the detection efficiency.

Characterization of large area photomultipliers and its application to dark matter search with noble liquid detectors

Abstract: There is growing interest in the use of noble liquid detectors to study particle properties and search for new phenomena. In particular, these detectors are extremely suitable for performing direct searches for dark matter. In this kind of experiment, the light produced after an interaction within the sensitive volume is usually read-out by photomultipliers. The need to go to masses in the tonne scale to explore deeper regions of the parameter space, calls for the use of large area photomultipliers. In this paper we address the need to perform laboratory calibration measurements of these large photomultipliers, in particular to characterize their behaviour at cryogenic temperatures where no reference data from the manufacturer is available. We present comparative tests of phototubes from two companies. The tests are performed in conditions similar to those of operation in a real experiment. Measurements of the most relevant phototube parameters (quantum efficiency, gain, linearity, etc.) both at room and liquid Argon temperatures are reported. The results show that the studied phototubes comply with the stringent requirements posed by current dark matter searches performed with noble-liquid detectors.

A Study of CsI(Tl) Scintillator with Optimized Conditions of Large Area Avalanche Photodiode

Abstract: Avalanche photodiode (APD) is a kind of photodiode that internally amplifies the photocurrent by an avalanche effect. The quantum efficiency of the APD is about 80% which is five times higher than that of typical photomultiplier tube (PMT). A 16 mm diameter of beveled-edge large area avalanche photodiode (LAAPD) made by Advanced Photonics was used for the CsI(Tl) scintillator characterization. A CsI(Tl) crystal was attached to LAAPD and energy spectra were measured with various γ-ray sources. Measurements of energy spectra of the CsI(Tl) crystal to optimize the energy resolutions were performed with different shaping time constants by shaping amplifier and with different gains by high voltage variation. The absolute light yield and energy resolution of CsI(Tl) crystals were measured with the LAAPD for 662 keV γ-rays from a 137Cs source. The LAAPD was calibrated with X-ray of 55Fe source for the calibration of the number of e-h pairs per channel. The absolute light yield of newly developed SrCl2 scintillat...

Absolute primary scintillation yield of gaseous xenon under low drift electric fields for 5.9 keV X-rays

Abstract: A standard gas proportional scintillation counter equipped with a photomultiplier tube has been used to measure the primary scintillation yield in Xe at 800 Torr for 5.9 keV x-rays. The value m = 53?8 was measured for the number of primary scintillation photons produced per absorbed 5.9 keV x-ray photon, which gives a value Ws = 111?16 eV for the average energy expended to produce a primary scintillation photon in Xe for this x-ray energy. The experimental method is based on a comparison between the primary and secondary scintillation signals measured with a digital oscilloscope, where the distinction of the small primary signal from the noise is achieved by always triggering the oscilloscope with the secondary scintillation signal, and making a time average over 128 primary/secondary scintillation pulses. No evidence for recombination scintillation was found. A qualitative discussion of Ws in terms of the ratio between excitation and ionization cross sections for electrons in Xe is also presented.

Single-photon-counting detector for increased sensitivity in two-photon laser scanning microscopy.

Abstract: We present the use and characterization of a photon-counting detector for increased sensitivity at low signal levels in fluorescence laser scanning microscopy (LSM). Conventional LSM photomultiplier tube detectors utilize analog current integration and thus suffer from excessive noise at low signal levels, introduced during current measurement. In this Letter we describe the implementation of a fast single-photon-counting (SPC) detector on a conventional two-photon laser scanning microscope and detail its use in imaging low fluorescence intensities. We show that for a low photon flux, the SPC detector is shot-noise limited and thus provides increased detection sensitivity compared with analog current integration.