The use of silicon photomultipliers for improving the time resolution of an electromagnetic calorimeter based on lead tungstate crystals

The use of S12572 MPPC silicon photomultipliers (Hamamatsu) for improving the timing characteristics of the PHOS electromagnetic calorimeter in the ALICE experiment at CERN is described. It is shown that by introducing an additional photodetector, that is, a silicon photomultiplier, it is possible, without worsening the energy resolution, to significantly improve the time resolution of the PHOS spectrometer from the current values of 3–4 ns to 150–200 ps.     

A light-emitting diode monitoring system of the PHOS photon spectrometer in the ALICE experiment on the large hadron collider

A light-emitting diode (LED) monitoring system of the PHOS photon spectrometer in the ALICE experiment on the CERN large hadron collider is described. The spectrometer includes three modules in the form of 64 × 56 matrices consisting of plumbum tungstate (PWO) crystals. As test light signal sources, Kingbright L934SCC superbright green light-emitting diodes with an individual instrumental regulation of light flash intensities in each channel of the spectrometer are used. The system ensures adjustment and monitoring of the electronics at the stage of preparing for the physical trigger of the PHOS modules and is intended to perform special test measurements with the spectrometer without using high-energy particles. In addition, in the course of the experiment, it allows one to promptly monitor each channel of the spectrometer and keep track of temperature variations of the light yield of the PWO crystals. In this case, the long-term relative channel monitoring stability is ensured at a 1.2 × 10⁻³ level.     

Studying the spectrometric characteristics of an ionizing-radiation detector based on a LaBr<Subscript>3</Subscript>(Ce) scintillator and a silicon photomultiplier

The intrinsic background of a LaBr₃(Ce) scintillator with a diameter of 5 mm and a height of 10 mm has been studied in comparison with LYSO and CeBr₃ scintillators. It is shown that due to its high energy resolution the detector based on a LaBr₃(Ce) crystal exhibits the lowest background count rate in a specified amplitude range. The measured energy resolution of the detector based on a LaBr₃(Ce) crystal with dimensions of Ø5 mm × 10 mm in combination with a silicon photomultiplier with an active area of 3 × 3 mm² are presented. It is demonstrated that a detector array with the proposed configuration (a scintillator + a silicon photomultiplier enclosed in a common container) exhibits an energy resolution of 4% for 661.7-keV γ rays and a background count rate of ~0.39 cps in the energy range of (140 ± 3σ) keV.     

Use of Large-Area Photodiodes for Improving the Characteristics of an Electromagnetic Calorimeter Based on Lead Tungstate Crystals

It is shown that an increase in the area of photodetectors allows the PHOS electromagnetic calorimeter of the ALICE experiment to operate at room temperature with better spectrometric characteristics. The linearity of the calorimeter response has been investigated in the 1–110 GeV energy range using both Hamamatsu S8664-1010 avalanche photodiodes with a large area (10 × 10 mm²) and arrays of MPPC Hamamatsu S12572-015C silicon photomultipliers with a sensitive area of 6 × 6 mm². The calorimeter based on avalanche photodiodes is linear in the energy range under investigation compared to a calorimeter composed of silicon-photomultiplier arrays.     

Study of the slow-fast preamplifier input parameter’s effects on output image for LYSO scintillator with PS-PMT based animal PET

We developed a small animal positron emission tomography with four detector heads, each one composed of 2 × 2 cm² of pixilated LYSO matrix of 10 × 10 crystals, 2 × 2 mm wide and 10 mm deep coupled to position sensitive photomultiplier (PS-PMT, Hamamatsu R8900U-00-C12). Anger-type logic discretized positioning circuit (DPC) multiplexed readout connected to PMT of each head. The fast-slow preamplifier is used in the fabricated animal PET. We showed that the input capacitance of the preamplifier (the capacitance in the output node of the resistive network) has a direct effect on output image. Image broadening, peak to valley ratio and the geometry distortion of crystal illustration are studied for different input capacitance of preamplifier. The input capacitance of 1 nF resulted in the best image by keeping all the parameters at the proper level with no geometry distortion at the edge of the image.     

A neutron tomograph at the IR-8 reactor of the National Research Centre Kurchatov Institute

A transmission neutron tomograph developed by the National Research Centre Kurchatov Institute is described. The tomograph is located at the monochromatic neutron beam of the fifth horizontal channel of the IR-8 research reactor. The neutron wavelength is 1.56 Å, the beam cross section is 50 × 40 mm², the field of view of the CCD-based detector system is 93 × 62 mm², and the spatial resolution at the sample position is ～400 μm. The internal structure of samples having different origin has been investigated.     

Studying the characteristics of the spectrometric detector based on a LaBr3:Ce crystal and a ФЭУ-184 photomultiplier tube

Results of investigations of the scintillation detector based on a LaBr₃:Ce crystal and a ФЭУ-184 photomultiplier tube are presented. It is shown that, optimizing the ФЭУ-184 photomultiplier tube circuit by reading out the signal from the next to last dynode, it is possible to utilize the spectrometric properties of the LaBr₃:Ce crystal.     

The Network Architecture of the Data-processing System for the Photodetector of an Orbital Detector of Ultra-high Energy Cosmic Rays

An orbital detector of ultra-high energy cosmic rays has been developed by the Skobel’tsyn Institute of Nuclear Physics of the Moscow State University together with the international JEM-EUSO collaboration for mounting on board the International Space Station. Its multichannel photodetector is composed of an array of multianode photomultiplier tubes (MAPMTs) combined into modules with 36 MAPMTs in each and with approximately 10⁵ pixels in total. Since the number of channels is great and the speed of measurements is high, high requirements are set for the system of detection, selection, and analysis of events. The designs of the modular photodetector composition and the network architecture of the data processing system that is capable of performing efficient selection of events with different space?time structures are presented. The network principle is implemented via three types of communications: high-speed links between adjacent photodetector modules, long-distance communications for recording information to the permanent memory, and synchronizing links for timing the operation of individual modules. This digital-processing system of the detector can be designed using the ZYNQ system-on-chip concept that includes a field programmable gate array and a processor system.     

Picosecond-resolution fluorescence lifetime measuring system with a cw laser and a radio

A procedure for measurement of fluorescence lifetimes with picosecond time resolution is described. A cw laser beam is modulated with a standing-wave acousto-optic modulator. The modulated beam is split; one part serves as a reference beam, the other part excites the fluorescent sample. The sample flourescence and the reference beam, attenuated and delayed optically to be equal in amplitude and opposite in phase to the fluorescence, are incident onto a single photomultiplier tube. The thus achieved photodetector ac null is monitored either by an AM radio, whose intermediate-frequency signal is displayed on an oscilloscope, or by a spectrum analyzer. With 30-MHz light modulation and the radio, lifetimes could be determined with resolution better than 15 ps. With the spectrum anlyzer and 170-MHz light modulation frequency we have achieved 4-ps lifetime resolution. Correction for photomultiplier transit time versus incident wavelength is made.     

激光等离子体X射线极化光谱研究

为了诊断激光等离子体X射线的极化光谱,研制了一种新型的基于空间分辨的极化谱仪。将平面晶体和球面弯晶色散元件在极化谱仪内正交布置,即在水平通道用PET平面晶体作为色散元件,而在垂直通道用Mica球面弯晶作为色散元件,球面半径为380mm。信号采用成像板进行接收,有效接收面积为30×80mm,从等离子体光源经晶体到成像板的光路约为980mm。物理实验首次在中国工程物理研究院激光聚变研究中心“2×10J激光装置”上进行,成像板获得了铝激光等离子体X射线的光谱空间分辨信号。实验结果表明该谱仪具有较高谱分辨率,适合激光等离子体x射线极化光谱的诊断。     

Scintillation γ spectrometers for use at nuclear power plants (review)

In this review, it is shown that out of the 300 scintillators synthesized to date only LaBr₃:Ce, CeBr₃, YAlO₃: Ce, and CsI:Tl crystals with the corresponding silicon photosensors (SiPSs) can be used as detectors in industrial γ-ray spectrometers intended for nuclear power plants. They are superior in their energy resolution and their resistance to mechanical and electromagnetic effects to spectrometers used today with a NaI:Tl crystal and a photomultiplier tube (PMT). A p–i–n photodiode (PD), an avalanche photodiode (APD), and a silicon photomultiplier (SiPM) are promising SiPSs. The properties of various assemblies of listed scintillators and photosensors are analyzed. A PD matches well with any scintillator. A spectrometer does not require LED stabilization of the scale, but its noise level must be reduced by selective PD cooling and the use of a light guide for coupling a massive scintillator and a SiPS with a small area of its sensitive surface. A spectrometer with an APD does not require photosensor cooling; however, LED stabilization of its energy scale is necessary. Application of an SiPM can rule out the use of a light concentrator (which is important for large CsI:Tl scintillators) and selective cooling, but this introduces nonlinearity at a short decay time and a high light yield in the scintillator (LaBr₃:Ce and CeBr₃) and also calls for an LED stabilization system for the spectrometer. The prospects for the development and application of new scintillation γ-ray spectrometers are discussed in this review.     

Prospective scintillation electron detectors for S(T)EM based on garnet film scintillators

The performance of a scintillation electron detector for a scanning electron microscope and/or a scanning transmission electron microscope (S(T)EM) based on new epitaxial garnet film scintillators was explored. The LuGAGG:Ce and LuGAGG:Ce,Mg film scintillators with chemical formula (Ce_0.01Lu_0.27Gd_0.74)_3–wMg_w(Ga_2.48Al_2.46)O₁₂ were prepared and their cathodoluminescence (CL) and optical properties were studied and compared with the properties of current standard bulk single crystal YAG:Ce and YAP:Ce scintillators. More specifically, CL decay characteristics, CL emission spectra, CL intensities, optical absorption coefficients, and the refractive indices of the mentioned scintillators were measured. Furthermore, electron interaction volumes with absorbed energy distributions, photomultiplier (PMT) photocathode matchings, modulation transfer functions (MTF), and the photon transport efficiencies of scintillation detectors with the mentioned scintillators were calculated. A CL decay time for the LuGAGG:Ce,Mg film scintillator as low as 28 ns with an afterglow of only 0.02% at 1 μs after the e‐beam excitation was observed. As determined from calculated MTFs, the scintillation detectors with the new film scintillators lose contrast transfer ability above 0.6 lp/pixel, while the currently commonly used YAG:Ce single crystal scintillators already do so above 0.1 lp/pixel. It was also calculated that the new studied film scintillators have an 8% higher photon transfer efficiency, even for a simple disk shape compared with the standard bulk single crystal YAG:Ce scintillator. The studied LuGAGG:Ce,Mg epitaxial garnet film scintillators were evaluated as prospective fast scintillators for electron detectors, not only in S(T)EM but also in other e‐beam devices.     

A scintillation γ-ray detector based on a solid-state photomultiplier

A scintillation detector based on a silicon photodetector of a new type—a solid-state photomultiplier—and a single-crystal CsI(Tl) scintillator was investigated. The effect of temperature on the low-energy detection threshold and the energy resolution of the detector and the influence of the radiation level on the detector efficiency (i.e., the influence of the counting rate of the distortion in the recorded spectrum shape) were estimated. A mathematical model of the detector was developed in order to assess its parameters.     

椭圆弯晶谱仪波长分辨能力的改进

讨论了椭圆弯晶谱仪的波长分辨能力。在假设谱线的固有宽度可以忽略的情况下,对两种实际影响椭圆弯晶谱仪波长分辨能力的主要因素,即光源空间尺寸和非理想椭圆分光晶面进行了分析。分别对上述两种情况进行了数学建模和数值模拟仿真。定量地分析了非理想椭圆晶面和光源空间尺寸对椭圆弯晶X射线谱仪波长分辨本领的影响程度,并给出了出射狭缝宽度与椭圆弯晶谱仪波长判读加宽的关系。从理论上论证了光源空间尺寸在限制谱仪的波长分辨能力方面仍然起关键主导作用;结合椭圆分光晶体的结构参数,合理地选择出射狭缝宽度,可使谱仪达到足够好的光谱分辨率和信噪比。用搭建的实验平台进行了实验测试,结果表明,当出射狭缝宽度(2δ)为10mm时,实测的谱线半高全宽(Δλ)为3.1×10-3nm;2δ为4mm时,Δλ为2.3×10-4nm,实测结果佐证了仿真结果的正确性。     

Multichannel linear detector for x-ray spectroscopy

This paper considers a new linear multichannel x-ray detector designed on the basis of a BLPP-369M4 silicon photodiode array (2612 photodiodes, array pitch 12.5 µm, height 4 mm, and dynamic range 10⁴). The structure and characteristics of the multichannel detector are given, along with the Kα1,2, Kβ ₁, and Kβ ₅ x-ray emission lines and a K-edge absorption spectrum of metallic copper recorded on a universal URS-2I spectrometer using this detector. The resolution and the signal/noise ratio of these spectra are superior to those of spectra recorded by an SRPP-21 gas ionization counter at the same recording time. The detector has a spatial resolution of 20 µm and an x-ray detection limit to equal 1 quantum at λ = 1.54 Å. It is suitable for studying the fine structure of absorption spectra at 1–10 Å.     

An air scintillator

A method for bremsstrahlung dosimetry by air luminescence at high-power pulsed electron accelerators is considered. Light emitted in an air scintillator is focused by the lens at the tip of a quartz optical fiber and transmitted to the photocathode of a photomultiplier tube. The sensitivity of the measuring channel is determined using a standard ribbon lamp. Bremsstrahlung pulses producing an exposure of 0.18 C/kg at the bremsstrahlung beam axis in a ∼20-ns time interval are detected at the ЛИУ-30 electron accelerator with a high accuracy. This exposure corresponds to an absorbed dose rate, integrated over the beam diameter, of 7.5 × 10⁷ Gy m/s.     

High-resolution,energy-dispersive microcalorimeter spectrometer for X-ray microanalysis

We have developed a prototype X-ray microcalorimeter spectrometer with high energy resolution for use in X-ray microanalysis. The microcalorimeter spectrometer system consists of a superconducting transition-edge sensor X-ray microcalorimeter cooled to an operating temperature near 100 mK by a compact adiabatic demagnetization refrigerator, a superconducting quantum interference device current amplifier followed by pulse-shaping amplifiers and pileup rejection circuitry, and a multichannel analyser with computer interface for the real-time acquisition of X-ray spectra. With the spectrometer mounted on a scanning electron microscope, we have achieved an instrument response energy resolution of better than 10 eV full width at half-maximum (FWHM) over a broad energy range at real-time output count rates up to 150 s^?1. Careful analysis of digitized X-ray pulses yields an instrument-response energy resolution of 7.2 ± 0.4 eV FWHM at 5.89 keV for Mn Kα_1,2 X-rays from a radioactive ⁵⁵Fe source, the best reported energy resolution for any energy-dispersive detector.     

A time-of-flight mass spectrometer for monitoring the inhalational anesthesia concentration in the real-time mode

The use of a medical mass spectrometer for measuring the concentration of the gas mixture components in the breathing circuit of an inhalational anesthesia machine in the real-time mode is described. The resolution of the mass spectrometer is M/ΔM = 200, and the detection threshold in terms of the partial pressure of the analyzed gases is 2 × 10^?12 mbar. The mass spectrometer is capable of measuring the volumetric content of CO₂, O₂, and inhalational anesthetic sevoflurane. The respiratory coefficient (CO₂/O₂) was measured during anesthesia to estimate the patient’s stress reaction to a surgical injury.     

A SMALL-ANGLE X-RAY SCATTERING STATION AT BEIJING SYNCHROTRON RADIATION FACILITY

This article presents the development and current state of a small-angle X-ray scattering station at beamline 1W2A of the Beijing Synchrotron Radiation Facility, China. The source of the beamline is introduced from a 14-pole wiggler. A triangular bending Si(111) crystal is used to horizontally focus the beam and provide a monochromatic X-ray beam (8.052 keV). A bending cylindrical mirror coated with rhodium downstream from the monochromator is used to vertically focus the beam. The X-ray beam is focused on the detector which is fixed at 30 m from the source. The focused beam size (full width at half maximum) is 1.4 × 0.2 mm² (horizontal × vertical) with a flux of 5.5 × 10¹¹ phs/s at 2.5 GeV and 250 mA. Besides the routine mode of small-angle X-ray scattering, the combination of small- and wide-angle X-ray scattering, grazing incidence small-angle X-ray scattering, and time-resolved small-angle X-ray scattering in sub-second level are also available for the users. Dependent on the measurement requirements, several detectors can be chosen for the collection of scattering signals. Furthermore, multiple sample environments, including temperature, stress-strain, and liquid sampling are available for in situ measurements. In a typical camera length of 1.5 m, the small-angle X-ray scattering resolution is about 115 nm. The steady operation of the small-angle X-ray scattering station at Beijing Synchrotron Radiation Facility not only provides the small-angle X-ray scattering beam time for users, but also promotes the development and application of these techniques in China.     

A BSE scintillation detector in the (S)TEM

A single crystal YAG: Ce³⁺ annular scintillator axially placed in a movable light guide forms the essential part of a new BSE detector. Comparison of properties of this detector with those of a semiconductor detector is made. The bandwidth, signal-to-noise ratio, capacitance effects, and relative efficiency are parameters which favour the scintillation detector. Its disadvantage is that it must be equipped with a photomultiplier and a light guide. The position of the scintillator above the specimen permits efficient detection at a large collection angle of BSE. For normal beam incidence, the signal homogeneity from any area of the scintillator ensures that images are obtained without shadow effects due to signal loss in the scintillator or due to detector geometry. The same probe current as for other detection modes can be used. Resolution of details is as high as for an SE image.