Methodical problems of crosstalk probability measurements in solid-state photomultipliers

Solid-state photomultipliers (SSPMs) is a new type of semiconductor avalanche photodetectors operating in the Geigermode with negative feedback and allowing detection of individual photons. In recent years, SSPMs are increasingly widely used in nuclear physics, high-energy physics, medicine, biology, and other fields, replacing vacuum photomultipliers and avalanche photodiodes (APDs). The negative feedback in SSPMs provides a high multiplication factor (10⁵–10⁶) and an ultralow noise factor (1.01–1.05); however, noises of crosstalk and afterpulsing processes come to the fore in this case. In this communication, we present the results of experimental measurements of crosstalk processes in various SSPM samples and analyze the measurement techniques.     

Lifetime measurement of the 23p state of helium

The lifetime of the 2³p state of He has been determined experimentally to be 125±7 nsec. The measurement was made using delayed coincidence with an invertron as the excitation chamber. A simple tunnel-diode preamplifier was designed to extend the usefulness of single photon counting photomultipliers into the infra-red.     

ZnS(Ag)/<Superscript>6</Superscript>LiF and LiI(Eu) scintillators and silicon photomultipliers for thermal neutron detectors with high space and time resolution

ZnS(Ag)/⁶LiF and LiI(Eu) scintillators for thermal neutron detectors have been investigated and neutron detectors based on these scintillators and photomultipliers have been tested. The efficiencies of these detectors are 5 and 66%, respectively. The possibility of developing position-sensitive detectors of thermal neutrons with high space and time resolution is discussed.     

Gamma-ray astronomy by the air shower technique: Performance and perspectives

Summary The techniques for γ-ray astronomy at energies ≥10 TeV using air shower detectors are discussed. The results, based on a number of large arrays, are negative, with no point sources being identified. While the contributions to γ-ray astronomy so far have been only upper limits, these arrays in the future will make significant progress in the understanding of cosmic rays in the energy range 10¹³ eV to 10¹⁶ eV. Also, contributions to solar physics are being made by observations of shape and time dependence of the shadow of the Sun as observed in cosmic rays. For the advancement of γ-ray astronomy a greater sensitivity is required in the energy region of 10 TeV. A number of promising techniques to accomplish a greater sensitivity are discussed. They include the enlargement of the Tibet array at 4300 meters altitude, the array of open photomultipliers at La Palma (AIROBICC), which views the shower by the Cherenkov photons produced in the atmosphere, and the instrumentation of a pond at Los Alamos with photomultipliers (Milagro). Invited talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Emission spectrum of intraband luminescence for single parabolic band under excitation of wide-band-gap insulators by ionizing radiation and particles

Emission spectrum and intensity of picosecond intraband luminescence for single parabolic band approximation of electron conduction band in insulating crystals are calculated. It is shown that the spectral intensity of this intraband emission increases approximately as (?ω)^?1/2 with decrease in photon energy, while the spectral density of photons increases as (?ω)^?3/2. The intensity of this emission is inversely proportional to the longitudinal optical phonon frequency. The total emission yield in this approximation is low, less than 10 photons in the spectral window of silicon photomultipliers per MeV of ionizing particle energy.     

Probabilistic distribution and noise factor of solid state photomultiplier signals,taking into account cross-talk processes

Solid-state photomultipliers (SSPMs) are a new type of photodetectors based on avalanche breakdown of the semiconductor in the Geiger mode, limited by negative feedback. Under such conditions, the avalanche breakdown is characterized by high multiplication factors, 10⁴–10⁶, and low noise, which allows detection of single photons. However, in practice, each primary breakdown in the SSPM can be accompanied by secondary breakdowns due to cross-talk processes which change the probabilistic distribution of the signal and introduce excess noise. In this paper, the effect of cross-talk on signal and noise characteristics of SSPMs is considered based on the generalized Poisson distribution.     

A multilayer scintillation detector of high-energy particles for satellite experiments

We describe the detecting system of a high-energy charged particle telescope spectrometer for a space experiment to be performed on the outer surface of the Russian section of the International Space Station and other spacecraft, including small satellites. The spectrometer’s detecting system is a multilayer scintillation detector (MSD) of polystyrene plates scanned by photomultipliers. It allows high-intensity fluxes of electrons (up to ～10⁵ cm^?2 s^?1) several milliseconds long with energies of 3 to 30 MeV to be measured with an accuracy of ～1 μs, along with time profiles and the evolution of particle energy spectra. The MSD is characterized by an energy resolution no worse than 10%, an angular resolution of ～10 degrees, a geometric factor of ～40 cm² sr, and a trigger system time resolution of ～20 ns.     

Stand for testing scintillation neutron detectors

A stand for studying the characteristics of time-of-flight neutron detectors is described. Plastic scintillation detectors in the form of rectangular prisms with cross sections of 100 × 100 and 100 × 200 mm² and lengths of 300, 400, and 500 mm are viewed through by photomultipliers from the two ends. The detectors are irradiated with a collimated 14-MeV neutron beam produced in the d + t → n+ ⁴He reaction. The collimated beam makes it possible to investigate the spatial resolution of long detectors. The interaction point is determined either from the arrival time of light pulses to the opposite ends of the scintillators or from the ratio of the amplitudes of the signals at the ends of the scintillators. The stand proposed also makes it possible to measure the absolute efficiency of detectors of different length at a neutron energy of 14 MeV.     

Digital positron lifetime spectroscopy at EPOS

As the digital equipment to measure positron lifetimes gets cheaper and more widely used, it is decided that EPOS, the ELBE positron source will sample the signals from the photomultipliers directly and evaluate it online or offline by digital means.Still using isotope sources, the EPOS lifetime spectrometer results in a timing resolution of around 170 ps (with ⁶⁰Co), which compares good to analog equipment. A distinct improvement is expected when a coincidence setup will be used at ELBE. However, also the software needs further improvement: while one of the goals is of course to achieve the best time resolution, there is also the aspect of runtime and expandability. Results of evaluations will be presented and compared with results from other groups.     

Recording of weak light fluxes by electron counting with photomultipliers

The amplitude distributions for noise sources are discussed in relation to the counting of single quanta with photomultipliers. It is shown that the best Russian photomultipliers have a sensitivity at room temperature exceeding that of the human eye and can be used to measure fluxes of 30–300 quanta per second.     

Evaluation of new large area PMT with high quantum efficiency

The neutrino detector of the Jiangmen Underground Neutrino Observatory(JUNO) is designed to use20 kilotons of liquid scintillator and approximately 16000 20 inch photomultipliers(PMTs).One of the options is to use the 20 inch R12860 PMT with high quantum efficiency which has recently been developed by Hamamatsu Photonics.The performance of the newly developed PMT preproduction samples is evaluated.The results show that its quantum efficiency is 30%at 400 nm.Its Peak/Valley(P/V) ratio for the single photoelectron is 4.75 and the dark count rate is 27 kHz at the threshold of 3 mV while the gain is at 1 × 10~7.The transit time spread of a single photoelectron is 2.86 ns.Generally the performances of this new 20 inch PMT are improved over the old one of R3600.     

Neutron capture gamma ray investigation of Sr88 level structure

The level structure of Sr⁸⁸has been investigated at the Karlsruhe research reactor FR2 using thermal neutron capture in Sr⁸⁷. A pure thermal neutron beam was obtained by Bragg reflection from a lead single crystal. The target was natural strontium which gives a cross section contribution of about 87% for the reaction Sr⁸⁷(n,γ) Sr⁸⁸. High resolution measurements of the capture gamma ray spectrum have been performed by means of a 4 cm² × 0.5 cm lithium-drifted germanium diode. 146 gamma lines have been observed. Cascade relationships were studied by a double and triple coincidence apparatus containing 4″Ø × 5″ NaI(Tl) crystals and XP-1040 photomultipliers. In several cases coincident background was subtracted utilizing the doublewindow technique. By application of the triple sum coincidence method capture gammas from isotopes other than the investigated Sr⁸⁸ nucleus could be eliminated. Several new levels were established. A transition scheme is proposed and discussed. The neutron binding energy of Sr⁸⁸ is determined to be 11111±4 keV.     

Spectroscopic measurements on a titanium plasma gun with hydrogenated electrodes

The plasma produced by a plasma gun which consists of concentric titanium and tantalum washers has been observed in the plasma gun as well as in a drift tube in which the plasma particles have been injected. Axial drift velocities of hydrogen and impurities have been determined in the drift tube by optical time-of-flight measurements. Maximum hydrogen velocities between 9·10⁶ to 1·10⁸ cm/sec could be determined, in agreement with magnetic probe-, Faraday cup-, microwave-, and electrostatic energy analyser measurements. The plasma which is produced within the plasma gun by a powerful discharge (vacuum arc) has been observed with a framing camera, spectrographs and photomultipliers. From end-on observed time resolved spectrograms the temperatures and electron densities have been determined as a function of time. The measurements indicate that thermal equilibrium is reached about 2·5 μsec after the firing of the main discharge. 4 μsec after the beginning of the main discharge a maximum temperature of about 72000° K is reached. The measurements further indicate that the high-energy part of the ejected particles is produced before an equilibrium state in the plasma gun has been established.     

Precision measurement of laser RF double resonance spectra with an effective compensation of residual magnetic field

Ultra Fast Timing has been applied at the IGISOL facility since more than a decade ago with the aim to systematically study nano- and subnanosecond lifetimes in the neutron-rich nuclei from the A~110 region. Over this period two generations of crystals and photomultipliers have been introduced, which allowed to study more complex level schemes populated in β decay. The IGISOL facility provides unique capabilities to study the A~110 region not matched elsewhere in the world.     

Using a LaBr3:Ce scintillator for positron annihilation lifetime spectroscopy

A LaBr₃:Ce scintillator has a high light output (~60000 p.e/MeV) and a short decay constant (<25 ns), which makes it good for time spectrometry. Compared with a BaF₂ scintillator, it can bear a much higher count rate, and can be coupled to photomultipliers without using a quartz window. In this work, a positron annihilation lifetime spectrometer (PALS) consisting of two bulks of φ25 mm×25 mm LaBr₃:Ce scintillator coupled to two XP20D0 photomultipliers, respectively, was built. A time resolution of FWHM=206 ps was measured for the PALS with a ⁶⁰Co source at the energy window for ²²Na. With this spectrometer, a reasonable lifetime value τ=221±4 ps in a pure Si sample is obtained, which means that the utilization of LaBr₃:Ce as the detector for a PALS is feasible.     

Development of radiation medicine at DLNP, JINR

The Dzhelepov Laboratory of Nuclear Problems’ activity is aimed at developing three directions in radiation medicine: 3D conformal proton therapy, accelerator techniques for proton and carbon treatment of tumors, and new types of detector systems for spectrometric computed tomography (CT) and positron emission tomography (PET). JINR and IBA have developed and constructed the medical proton cyclotron C235-V3. At present, all basic cyclotron systems have been built. We plan to assemble this cyclotron at JINR in 2011 and perform tests with the extracted proton beam in 2012. A superconducting isochronous cyclotron C400 has been designed by the IBA-JINR collaboration. This cyclotron will be used for radiotherapy with proton, helium and carbon ions. The ¹²C⁶⁺ and ⁴He²⁺ ions will be accelerated to an energy of 400 MeV/amu, the protons will be extracted at the energy 265 MeV. The construction of the C400 cyclotron was started in 2010 within the framework of the Archarde project (France). Development of spectrometric CT tomographs may allow one to determine the chemical composition of a substance together with the density, measured using traditional CT. This may advance modern diagnostic methods significantly. JINR develops fundamentally new pixel detector systems for spectrometric CT. The time-of-flight (TOF) system installed in the positron emission tomograph (PET) permits essential reduction in the detector noise from occasional events of different positron annihilations. The micropixel avalanche photodiodes (MAPDs) developed at JINR allow a factor of 1.5 reduction in the resolution time for the PET TOF system and suppression of the noise level as compared to commercial PET. The development of a combined PET/MRI is of considerable medical interest, but it cannot be made with the existing PET tomographs based on detectors of compact photomultipliers due to strong alternating magnetic field of MRI. Change-over to detectors of micropixel avalanche photodiodes permits making a combined PET/MRI.     

磁调制光电倍加管的超光度计

一.序言和一般概念 1.1问题的提出 在应用物理和物理化学方面,弱光的量测逐渐占有重要的地位。愈来愈多的材料的物理性质和化学性质是间接或直接采用光学方法测定的。纯科学的发展、它在技术上的应用以及工业上的需要不断地推动着量测弱光的方法,要求它变得更加灵敏和稳定可靠。由于采用燐光体和闪烁晶体作为能量转换器的X射线定量量测和核子辐射的量测广泛地被使用,这一问题的重要性愈益增加。弱光量测方法的灵敏度数量级如果有相当大的增加,就可以在工业上安全地应用放射性同位素,而不致像目前那样被认为只是实验室的一种方法。     

OBSERVATION OF CERENKOV LIGHT FROM EXTENSIVE AIR SHOWER

The pulse shape and the intensity of Cerenkov light from extensive air shower have been recorded by using two different types of photomultipliers (fast and slow).The distribution of the FWHM of Cerenkov light pulse and the spectrum of Cerenkov photo density have been measured for E>5×10¹⁴eV,at sea level.Comparing the two intensity results from two types of tubes indicate that the system which consists of the slow tubes and the peak ADC is not only simple but also cheap for the Cerenkov light intensity measurement.     

Ultrashort laser-pulse diagnostics for detection of ordering within an ion beam

A novel diagnostic method to detect ordering within one-dimensional ion beams in a storage ring is presented. The ions are simultaneously excited by a ultrashort pulsed laser ( 1 ps) at two different locations along the beam and fluorescence is detected by a group of four photomultipliers. Correlation in fluorescence signals is a firm indication that the ion beam has an ordered structure.     

?erenkov radiation in large cosmic-ray air showers

Summary A synchronized array of fast photomultipliers has been used to reconstruct the image in Ĉerenkov light of individual large cosmicray showers high in the atmosphere. The details of the images are in agreement with simulations based upon conservative models for cascade development. Observation of the fluctuations of the image between showers may enable the mass of the energetic cosmic rays to be determined.

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Riassunto Si è usato un sistema sincronizzato di fotomoltiplicatori veloci per ricostruire l'immagine in luce di Ĉerenkov di grandi sciami distinti di raggi cosmici, alti nell'atmosfera. I dettagli delle immagini sono in accordo con simulazioni fondate su modelli conservativi per lo sviluppo a cascata. L'osservazione delle fluttuazioni dell'immagine tra gli sciami può permettere la determinazione della massa dei raggi cosmici energetici.