Anode Output Research Articles

A position-sensitive γ-ray detector for positron annihilation 2D-ACAR based on metal package photomultiplier tubes

A new position-sensitive γ-ray detector to be used in a two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) apparatus has been developed. It consists of 36 compact position-sensitive photomultiplier tubes (PS-PMT: HAMAMATSU R5900-00-C8), a light guide, and 2676 Bi 4Ge 3O 12 (BGO) scintillator pieces of size 2.6 mm×2.6 mm×18 mm. A high detection efficiency for 511 keV γ-ray is achieved with the length of BGO scintillators used. The detection area is about 160 mm×160 mm. The 288 anode outputs of the PS-PMTs are wired and connected to resistor chains from which 16 outputs (8 outputs each along the X and Y directions) are taken to identify the incident position of the γ-ray. The spatial resolution is about 3 mm (FWHM). The timing signal taken from the last dynodes of the PS-PMTs gives a timing resolution of 7.7 ns (FWHM) for 511 keV positron annihilation γ-rays.

Scintillator identification and performance characteristics of LSO and GSO PSPMT detector modules combined through common X and Y resistive dividers

Combining signal channels from detector arrays can reduce complexity and minimize cost but, potentially, at the expense of other performance parameters. The authors evaluated a method that reduces the number of signals by combining the anode outputs of three position-sensitive photomultiplier tubes (PSPMTs) through a common X resistive charge divider and three individual Y resistive charge dividers. Field flood images at 511 keV of two LSO modules combined with a single GSO module were compared to images obtained when the modules were illuminated separately. At moderate count rates only a small reduction in position detection accuracy was observed in the combined tubes. Event mis-positioning was minimal for total count rates <300,000 cps. At higher rates, pulse pileup degraded accuracy. Delayed charge integration, a method for identifying scintillators by differences in their light decay times, allowed the LSO and GSO arrays to be distinguished from one another and also reduced the effect of pulse pileup. Thus, combining PSPMTs anodes through common X and common Y resistive dividers may be useful in reducing signal number from PSPMT detector modules while maintaining good event localization and scintillator identification accuracy at reasonable event rates.

Zero dead time spectroscopy without full charge collection

The Savannah River Technology Center has built a remote gamma monitoring instrument which employs data sampling techniques rather than full charge collection to perform energy spectroscopy without instrument dead time. The raw, unamplified anode output of a photomultiplier tube is directly coupled to the instrument to generate many digital samples during the charge collection process, so that all pulse processing is done in the digital domain. The primary components are a free running, 32 MSPS, 10-bit A/D, a field programmable gate array, FIFO buffers, and a digital signal processor (DSP). Algorithms for pulse integration, pile-up rejection, and other shape-based criteria are being developed in DSP code for migration into the gate array. Spectra taken with a 2 in NaI(Tl) detector have been obtained at rates as high as 59 000 counts per second without dead time with peak resolution at 662 keV measuring 7.3%.

Two types of electrochemical nitric oxide (NO) sensing systems with heat-denatured Cyt C and radical scavenger PTIO

To develop an in situ NO sensing system for primarily biological and medical uses, two types of NO sensing materials, which may be coupled with an electrochemical reaction for signal transduction, have been investigated. Heat-denatured Cyt C and a radical scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetra methyl imidazoline-1-oxyl-3-oxide (C-PTIO) were found to be effective and were incorporated into electrochemical sensing systems. Heat-denatured Cyt C deposited on a 4-mercaptopyridine modified gold electrode responded to NO with an increase of cathodic current through electrochemical reduction of Cyt C (Fe 3+), when the electrode potential was controlled at 0 mV vs Ag/AgCl. The dynamic range of the sensing system was 0.5–4 μM. The sensing system with C-PTIO exhibited an anodic output in response to NO at 0.7 V vs Ag/AgCl, and showed a wider dynamic range from 0.05 to 100 μM.

MCBETH: liquid scintillation counting spectra computation at the dynodic output of the photomultipliers

This paper presents a Monte Carlo based FORTRAN code to generate the final electron pulse height spectrum obtained at the anode of a liquid scintillation counting system. The code simulates the detection of beta particles in a toluene scintillator, the generation of photoelectrons, the subsequent electron amplification by a single photomultiplier tube or by two photomultipliers working in summed-coincidence mode, the final anode output pulse, and eventually the pulse-height histogram.

Evaluation of time measurement precision in the Counting Test Facility of the Borexino experiment

Abstract The Counting Test Facility, the prototype of the Borexino experiment installed at the Gran Sasso Laboratory, is an unsegmented liquid scintillator detector in which the spatial reconstruction of the events plays an important role. The event localization is performed through a time of flight technique, which exploits the time informations of the signals of the photomultipliers detecting the photons escaping from the 4 tons scintillation sphere in the center of the detector; thus the uncertainty affecting the time measurement of each anode output represents the ultimate limit on the achievable spatial resolution. This uncertainty has been evaluated through analytical and Monte Carlo calculations based on the actual characteristics of the photomultipliers and of the scintillator adopted for the detector. In this work we present in detail the model assumed to perform the calculations together with the main results obtained.

Gain stability of photomultipliers at high variable counting rates

Abstract The gain stability and the temperature effects of three photomultiplier tube bases at high counting rates were tested experimentally. Comparisons of the gain variation with counting rate were made among different supply voltages and between anode and dynode output signals. The factors causing gain variation at high counting rates were discussed. The experiments show that, choosing a transistor emitter follower type, using a lower supply voltage and adopting a dynode output mode are effective measures for improving the gain stability.

Proximity Focused Microchannel Plate Photomultiplier Tubes

Several forms of microchannel plate photomultiplier tubes (MCP PMT) for both high speed and multiple anode output applications are discussed. These tubes are from one MCP, with moderate gain, to three MCPs for photon counting gain levels. Proximity focus maintains distortion-free imaging through the tube structure. Performance data on photocathode types, gain, background, for each tube type is given.

Fatigue Effects on the Area Sensitivity, Dynode Gain, and Anode Output for Several End-on Photomultipliers

Instrumentation was developed to determine the time dependent effect of incident illumination on the area sensitivity and the gain stability of photomultipliers. Five end-on, S-11 photomultipliers were tested (6292, 2020, 6342A, 6655A, and 8053). The anode current variations were measured for a period of 3 h, the last three dynode gains were calculated, and the area sensitivity maps of these photomultipliers were recorded for several levels of illumination. It was found that: (1) with a constant light input to the multipliers tested, the output (anode current) varied up to 10% for the most stable tube (6342A) to over 400% for the most unstable tube (6292); (2) the relative sensitivity over each tube face (photo-cathode) area remained unchanged; (3) the photomultipliers can recover to more than one internal state (the condition of the dynode surfaces); (4) the variation of photomultiplier gain with time depends on the dynode structure and coating; (5) the earlier stages contribute as much to gain instability as do the last three stages; (6) the focus electrode voltage producing the most uniform area sensitivity differs slightly (~5%) from the voltage for maximum anode current.

Electronic elimination of noise pulses in scintillation counting

This paper describes the principle of operation and the performances of a circuit designed for electronic elimination of noise pulses in a scintillation spectrometer. The circuit makes use of the fact that the photoelectron which are released at the cathode of the photomultiplier due to a single scintillation flash are not exactly coincident in time, since the respective photons are emitted according to the transient decay characteristics of the involved scintillator. Because more than one noise pulse (single electron pulse) within the decay time τ is highly improbable to occur, the pulses consisting of two or more photoelectrons within τ, are signal pulses originating from a scintillation flash. These pulses are accepted, whereas noise pulses are discriminated by means of the fast photomultiplier able to resolve a signal pulse into its sequential single electron pulses and by means of a difference amplifier which compares the amplitudes of an integrated dynode output and a differentiated anode output of the photomultiplier. The limits of this elimination principle and the resulting design features are discussed. The spectrometer presented makes use of the high speed RCA C 70045 D photomultiplier. Both slow and fast scintillators can be used. The elimination circuit decreases the noise count rate to about 5% of its original value. The experimental results are illustrated with pulse height spectra obtained with various scintillators and radioactive sources. The measurements show that a further decrease of the residual noise count rate to less than 0.1% of its original value can be achieved if the arrangement is to operate with fast scintillators only.

An Application of Cathodic Protection To the Inside of a Tank

Abstract A 10,000 barrel bolted tank was found to have developed active internal corrosion within an eight year period. The tank was then coated on inside bottom and two feet up on the shell with a coal tar product, and steam coils were installed. ‘After 12 years’ additional service it was found that four leaks had developed in the tank. It was again cleaned, the steam coils removed, and the tank visually inspected. Welded repairs were made to the tank and the coating was repaired. Four 9 pound magnesium anodes were installed at this time and 6 inches of water were placed in the tank to serve as electrolyte. Anodes were installed so that they could be inspected or replaced while the tank was in service; records were made of anode outputs, driving potential, anode efficiency and tank-to-electrolyte potential. Current outputs were restricted and the 9 pound anodes ultimately were replaced with 17 pound anodes. A measured output of 666 ampere-hours/pound was obtained from one of the 9 pound anodes. It is cal...