Photomultiplier Pulse Research Articles

An Analysis of the Light Yield in a Plastic Scintillator as a Function of the Electron Energy

While preparing for an experiment on the search for neutrinoless double β decay of 150Nd nuclei, the spectrometric properties of polystyrene were investigated, including the dependence of the photomultiplier pulse amplitude on the energy of detected electrons. It is shown that a good description of experimental data is attained by taking the energy loss in passive materials, changes in the ionization density at low energies, and additional light due to Cherenkov radiation generated in polystyrene into account.

Determining the muon mass using a scintillator-based detector

A scintillator-based detection system, of the type employed in the popular muon-lifetime instructional lab experiment, is used to measure the muon mass. The photomultiplier pulse pairs produced by the decay of cosmic ray muons into product electrons and positrons within the scintillator are detected by a digitizing oscilloscope and the energies of the product particles are quantified by integrating the area under their associated pulses. The observed distribution of product-particle energies is then compared with Monte Carlo simulated distributions assuming different values of the muon mass mμc2, where the modeling of product-particle energy loss within the scintillator accounts for collisional and radiative effects in a detailed way. Via a least-squares comparison, it is found that the simulated distribution based on a value of mμc2=105±5 MeV most closely matches the experimental distribution.

Control System Development for a Raman Spectrometer Using Microcontroller Technology

An electronic control system has been developed for a Raman spectrometer by using electronics based on microcontrollertechnology. With these microcontrollers it is possible to emulate control circuitry capable of performing complex tasks, suchas the monochromator step motor control and the photomultiplier pulse count required in the Raman spectroscopy process.This approach could be used to give new life to valuable scientific instruments and tools. The Raman spectrometer controlbuilt is now fully functional and compatible with Windows 7. Raman spectra from well-known materials are presented tocompare results and in order to confirm the proper operation of the developed control system.

System Modeling and Design Optimization for a Next-Generation Unattended Sensor

We are developing a next-generation unattended sensor that can detect and identify radiation sources while operating on battery power for several weeks. The system achieves smaller size and weight over systems that use NaI:Tl and 3He detectors by using a relatively new scintillator, Cs2LiYCl6:Ce (CLYC). This material can detect both gamma rays and thermal neutrons, has best-case energy resolution under 4% full width at half maximum at 662 keV, and allows for particle discrimination by pulse amplitude as well as pulse shape. The overall design features an array of sixteen CLYC detectors, each read out by a photomultiplier tube and custom pulse processing electronics. A field-programmable gate array analyzes the energy spectra using computationally efficient algorithms for anomaly detection and basic isotope identification. In this paper, we report the results of a modeling study to optimize various parameters of the unattended sensor for best performance. Key parameters include the number and placement of detectors, dimensions and weight of the moderator, and location of the batteries. These results have guided the design of the proof-of-concept prototype.

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.

Photomultiplier pulse Read Out system for the preshower detector of the lhcb experiment

The second generation experiment for CP violation studies in B decays, LHCb, is a 20-m-long single-arm spectrometer to be installed on the future Large Hadron Collider at CERN. For its precision measurement purpose, it combines precise vertex location and particle identification, in addition to a performance trigger system able to cope with high flux. The first level of trigger is mainly based on the fast response of the calorimetric subsystem. Of major importance is the 6000 channels preshower detector that aims to validate the electromagnetic nature of calorimetric showers. It consists of two-radiation-length lead sheet in front of a scintillator plane. Scintillator signals are extracted from plastic cells using wavelength-shifting fibres coupled to multi-anode photomultiplier tubes. The preshower Read Out system has to cope with fluctuating photomultiplier pulses caused by small amounts of photoelectrons, in addition to strong constraints imposed by the 40MHz LHC bunch-crossing frequency.A special Read Out electronics including perfect 40MHz integrators able to shape fluctuating photomultiplier pulses has been designed, and successfully realized. The temporal shape of photomultiplier pulse and the upstream Read Out system for preshower are described in this document.

Beam test of Cherenkov counter prototype for ZDF setup

Abstract In this paper we describe a Cherenkov counter of total internal reflection for particle separation in the momentum range where all types of particles radiate Cherenkov light. The Cherenkov counter prototype with the lucite radiator was tested on the secondary beam of the ITEP (Moscow) accelerator. Dependence of the photomultiplier pulse height on the particle entrance angle was clearly observed.

High-pass filtering extends the dynamic range for recording pulse shapes

When a roughly flattopped pulse electrical pulse is recorded by a digitizer, signal clipping can destroy information that is crucial to the experimenter. This is particularly true in release-overtake shock experiments, where the occurrence time of a change in slope at the top of a photomultiplier pulse is sought. We have invented a simple and accurate method to record the pulse that is robust to clipping. The digitizer records the signal through a high-pass circuit. The inverse of the high-pass filter is applied via fast Fourier transform during analysis. The insensitivity to clipping allows one to record the change in slope signature at a higher gain, and thus with an improved signal to noise ratio. The technique is generically applicable to any recording of a roughly flattopped pulse.

Study of n-γ discrimination by digital charge comparison method for a large volume liquid scintillator

The study of the n-γ discrimination for a large 4 I volume BC501A liquid scintillator coupled to a 130 mm diameter XP4512B photomultiplier was carried out by digital charge comparison method. A very good n-γ discrimination down to 100 keV of recoil electron energy was achieved. The measured relative intensity of the charge integrated at the slow component of the scintillation pulse and the photoelectron yield of the tested counter allow the factor of merit of the n-γ discrimination spectra to be calculated and to be compared with those measured experimentally. This shows that the main limitation of the n-γ discrimination is associated with the statistical fluctuation of the photoelectron number at the slow component. A serious effect of the distortion in the cable used to send the photomultiplier pulse to the electronics for the n-γ discrimination was studied. This suggests that the length of RG58 cable should be limited to about 40 m to preserve a high quality n-γ discrimination.

Lifetime Analysis of Weak Emissions and Time-Resolved Spectral Measurements with a Subnanosecond Dye Laser and Gated Analog Detection

A relatively inexpensive UV fluorometer has been developed for the temporal and spectral characterization of weak emissions, with the use of a frequency-doubled nitrogen-pumped dye laser for excitation wavelengths down to 260 nm. Gated detection of the photomultiplier pulse provides 0.1-ns resolution of the 1.4-ns FWHM instrument response function. On-line statistical measurements characterize the waveforms, with NATA, tryptophan, and NADH as model compounds providing emission signals of the order of the water Raman scatter signal. Time-decay waveforms are analyzed with the use of nonlinear least-squares fitting, with scatter or p-terphenyl as the reference, and a time shift. Good agreement with the literature is found for the subnanosecond and nanosecond decay times, with resolution of multiple decays down to several percent fractional emission. With multichannel data acquisition, a set of time-windowed emission spectra can be obtained in the same period as is required for an additional time-decay waveform. Time-windowed spectra and the derived decay-associated spectra provide evidence concerning the decay model in addition to spectral characteristics. Practical limitations include the peak current linearity of the photomultiplier and the wavelength variation of the response function.

High Resolution Time-of-Flight Electronics System

A new electronics system for time-of-flight measurements has been developed to meet the performance requirements of the Mark II Detector for operation at the PEP Storage Ring of the Stanford Linear Accelerator Center. This system incorporates high resolution time measurements with the capability to correct systemic errors from the scintillator and photomultiplier tubes. The correction technique involves making three measurements on each photomultiplier signal every storage ring beam interaction. Two timing measurements are made relative to the beam interaction time with different discriminator threshold level settings. The charge integral of each photomultiplier pulse is also recorded. These multiple measurements allow computer correction of errors due to discriminator walk with pulse amplitude, timing errors due to scintillator light attenuation and spread, and finite risetime limitations of the photomultiplier and cabling. The system can be quickly reset after each beam interaction if there is no trigger, thus eliminating any need for delay cables in photomultiplier signal cabling. The electronics designed for the new time-of-flight system is the subject of this paper.

Computed intrinsic efficiencies and modulation transfer functions for gamma cameras

For the two crystal materials, NaI(Tl) and CsI(Na), total, photoelectric and photopeak efficiencies are derived at several gamma -ray energies and crystal thicknesses. The effects of the stochastic variations in photomultiplier pulse production and of multiple Compton events on resolution are combined so as to give the modulation transfer function of gamma cameras without collimators. The effect of a hypothetical Compton discrimination on sensitivity and resolution is discussed.

On the intrinsic resolution of a gamma camera system

Theoretical simulation of the Anger gamma camera system on a digital computer was used to study the dependence of the intrinsic resolution on the stochastic nature of the photomultiplier pulse formation, as well as on some design parameters. A simple analytical model was found to give similar results on a relative basis. A substantial improvement in resolution is obtained by a proper choice of light-guide material and by introducing specular reflection at the crystal front surface.

Deadtime corrections reduced by electronics

The deadtime of a counting system composed of scintillator, photomultiplier, window-discriminator and counter, was reduced from 20 nsec to about 2 nsec. The improvement was achieved by using the ability of the discriminator to eject more than one logic impulse depending on the duration of the photomultiplier pulse.

Time Dependence of Scintillations and the Effect on Pulse-Shape Discrimination

The time dependence of the light following excitation by gamma rays and neutrons was measured for stilbene and for the liquids NE-213, NE-213M, and NE-218.+ In addition, the number of photoelectrons produced at the cathode of an RCA-8575 photomultiplier per keV energy loss in the scintillator has been determined for each of these scintillators. A straightforward technique for pulse-shape discrimination is described; it consists in measuring the time difference between the start and the instant at which the integrated photomultiplier pulse reaches a specified fraction of its final amplitude. From the measured scintillation decay, the probability distribution of these rise times has been calculated for different fractions and for different photon and neutron energies on the assumption of Poisson statistics. These calculated distributions are in agreement with the experimental results obtained with the above-mentioned technique. The pulse-shape discriminating system is very stable and will accept 80% of the neutrons at 350 keV and only approximately 1% of the gamma rays producing scintillations with equal integrated light.

A New Approach to High Resolution Timing with Photomultipliers

A new technique (Double Sampling) of photomultiplier pulse processing is studied in order to improve the time resolution. Two time references, t1, and t2, are obtained from two different processing systems, into which the fast pulse of the photomultiplier is fed. If the condition: (t1 - t2) -?t < (t1 -t2) < (t1 - t2) + ?t is satisfied, the pulse is accepted for the time analysis. ?t is a predetermined parameter of the proposed system. A theoretical study has been carried out in order to compare this processing method with the ones already used.

A photomultiplier pulse shaper with minimal time slewing, incorporating a tunnel diode cascade trigger circuit

An instrument is described that converts signals from photomultipliers into pulses of standard amplitude (10 mA) and adjustable width (2.5–100 ns). It consists of an input shaping network, of which two versions are given, and a tunnel diode cascade trigger circuit. An attempt has been made to reduce the time slewing to a minimum: with input pulses ranging from 10–160 mA, from a 56 AVP photomultiplier, it remains within ±0.25 ns. The instrument is capable of working up to frequencies of 150 Mc/sec.

Pulse shaping and standardizing of photomultiplier signals for optimum timing information using tunnel diodes

Accurate timing signals have been derived from fast photomultiplier pulses by differentiating the photomultiplier pulse in order to produce a zero-crossing signal whose time of zero crossing is fixed over a large dynamic range of light level. Detection of the zero-crossing point is accomplished with a balanced-bridge tunnel-diode discriminator, which produces a standardized output of 100-mV amplitude, and a half-width of 4 nsec. A balanced bridge is used to prevent the zero-crossing signal from appearing at the output. For a twenty-to-one range of photomultiplier-input light level, the time shift of the output pulse may be as low as 0.5 nsec with a change in the output amplitude of less than a factor of two. When this discriminator is used with a 14-stage photomultiplier, the sensitivity is great enough to allow direct operation from single photo-electrons. The above numbers are an indication of what one can obtain with the tunnel diode and transistor combination chosen at the time of the original development almost two years ago. Since that time, particularly in the tunnel-diode field, numerous improved devices have become available. We are currently evaluating these in zero-crossing circuits. The zero-crossing photomultiplier pulse has been generated in two ways. The first method uses an overdamped LC-tuned circuit built into the base of a 6810-A photomultiplier. Here the time of zero crossing is controlled by the frequency of the LC-tuned circuit. The decay time of the scintillation plastic used and the rise time of the photomultiplier determine what this zero-crossing time should be. A clipping stub has also been used to produce the zero crossing remotely from the photomultiplier. By this method, one can control the zero-crossing time by both the length and impedance of the clipping stub.

Untersuchung der Elektronenkomponente von Einzellawinen mit dem Photomultiplier

With a photomultiplier single electron avalanches of 103 carriers can be observed in nitrogen. 2.5% of all photons (in the range 3000≦λ≦7000 A) of an avalanche produce a photoelectron at the cathode of the photomultiplier. The influence of the variable solid angle on the photomultiplier pulse is given. Trouble by noise is calculated and it is shown that the information depends on the number of photoelectrons only. The electron components of avalanches in methane, nitrogen, and mixtures have an exponential rise and the measured rise time constant τbeob is in accordance with the theoretical value 1/αυ_. For carrier numbers >106 space charge influence is observed, as given by theory. The quantum efficiencyQ per ionizing impact is found to beQ∼10−3 in vapours andQ∼1 in gases. Values of the electron drift velocity in mixtures of N2 and CH4 are given.

Scintillation Response of Anthracene to Low-Energy Protons and Helium Ions

Photomultiplier pulse amplitudes produced by light from anthracene crystals bombarded by protons and helium ions from 25 to 375 kev were measured. Both response curves (pulse height vs energy) are nonlinear, but that for protons bends away from the energy axis while that for helium ions bends towards it. Both curves extrapolate smoothly to the origin, indicating an absence of any nonscintillating surface layer more than about 10 kev thick. Present knowledge of stopping cross sections ($\frac{\mathrm{dE}}{\mathrm{dx}}$) for anthracene is inadequate to permit an unambiguous determination of the specific fluorescence ($\frac{\mathrm{dL}}{\mathrm{dx}}$) from the observed pulse amplitudes. However, some qualitative conclusions can be drawn concerning Birks' theory of the fluorescent process.