Output Pulse Height Distribution Research Articles

Liquid Scintillators Neutron Response Function: A Tutorial

This tutorial is devoted to the understanding of the different components that are present in the neutron light output pulse height distribution of liquid scintillators in fusion relevant energy ranges. The basic mechanisms for the generation of the scintillation light are briefly discussed. The different elastic collision processed between the incident neutrons and the hydrogen and carbon atoms are described in terms of probability density functions and the overall response function as their convolution. The results from this analytical approach is then compared with those obtained from simplified and full Monte Carlo simulations. Edge effect, finite energy resolution, light output and transport and competing physical processes between neutron and carbon and hydrogen atoms and their impact on the response functions are discussed. Although the analytical treatment here presented allows only for a qualitative comparison with full Monte Carlo simulations it enables an understanding of the main features present in the response function and therefore provides the ground for the interpretation of more complex response functions such those measured in fusion plasmas. Although the main part of this tutorial is focused on the response function to mono-energetic 2.45 MeV neutrons a brief discussion is presented in case of broad neutron energy spectra and how these can be used to infer the underlying properties of fusion plasmas via the application of a forward modelling method.

The Effect of Depletion Layer Thickness in Avalanche Photodiodes for Measurement of Low-energy Electrons

We have tested APDs (Type spl 3989 and Z7966, Hamamatsu Photonics K.K.) using an electron beam. The Z7966, which has a depletion layer of 10 μ m , is firstly focused on and tested in our former paper [K. Ogasawara, K. Asamura, T. Mukai, Y. Saito, Nucl. Instr. and Meth. A 545(3) (2005) 744] for the energy range of 5–20 keV. The result shows that the pulse height distribution of the APD signal exhibits a significant peak for electrons with energies above 8 keV, and positions of their peaks show a good linearity. The condition of the peak production at energies below 8 keV was attributed to the thickness of the dead layer on the surface of APDs. Now we have tuned up our electron acceleration system up to 40 keV, and tested Z7966 by electrons of higher energies. The result shows that the output pulse height distributions of this Z7966 were distorted over 30 keV. In order to examine the distortion of pulse height distributions, we have made a Monte Carlo numerical simulation of particle transport inside the APD. The result shows that the highest energy limit is expected to be determined by the thickness of the depletion layer inside the APD. Therefore, we have tried an APD type spl 3989, which has a thicker depletion layer ( 30 μ m ) and a thinner dead layer. As is expected, the spl 3989 responded to 2–40 keV electrons with fine peaks in the output pulse height distributions. The energy resolution was lower than 1 keV for 2–20 keV electrons, and 5 keV for 40 keV electrons. The linearity of the response was also good. According to the Monte Carlo simulation, electrons up to about 60 keV are expected to be well detectable.

Dissociation of electronically excited D3O to O+D2+D from the glancing charge transfer reaction of D3O+ with H2O

A method based on a microchannel plate particle detector’s output pulse height distributions has been used to specify the masses of product fragments in the glancing collisional charge transfer reaction of D3O+ with H2O. The predominant product channel involves D3O→O+D2+D.

Investigation of Large Format Microchannel Plate Z Configurations

The performance of triplet (Z) stacks of microchannel plates (MCP's) has been studied as a part of the instrument development for the Extreme Ultraviolet Explorer [1] (EUVE) satellite mission. Relatively large MCP's with a 60 mm diameter and having an 80:1 channel length to diameter (L/D) ratio were used in several configurations. These have been used in the EUVE prototype imaging detector to provide > 512 × 512 pixels with low image distortion (< 1%). We have examined the gain and pulse height characteristics showing that both high gains (> 2 × 107) and tight output pulse height distributions (< 30% FWHM) may be achieved. Simple distribution techniques have also allowed low intrinsic background event rates (< .15 events cm-2 sec-1) to be obtained. Variation of the quantum efficiency of MCP's over the wavelength range 160 Å to 1216 Å has been investigated for a range of angles of incidence. The effect of temperature variations on MCP operating characteristics has also been evaluated.

Size Distribution Measurement of Airborne Coal Dust by Optical Particle Counters

An optical particle counter has been calibrated for size distribution measurement of airborne coal dust particles. A differential electrical mobility analyzer was used with a fluidized bed dust feeder to produce uniform coal dust particles of a known size for calibration for particles <2.4 μm. For larger particles, the optical counter was calibrated with a microscopic technique. The output pulse height of the optical counter was found to be significantly lower for coal particles than for spherical oil drops of the same particle size. The geometrical standard deviation, σg, of the output pulse height distribution of the optical counter for monodisperse aerosols was found to increase from about 1.1 for spherical oil particles to about 1.8 for the irregularly shaped coal particles. Although this broadening effect reduced the ability of the counter to resolve small particle size differences, a numerical inversion procedure was developed which allowed the original size distribution to be recovered.

Preliminary results with saturable microchannel array plates

Microchannel array plates with a performance comparable to that of a conventional channel electron multiplier have been obtained for the first time. These array plates employ an angled electrostatic field to inhibit the feedback of positive ions within the microchannels. Saturated output pulse height distributions with modal gain values in excess of 107 have been obtained and stable operation demonstrated over a range of ambient pressures from 1×10−7 to 8×10−5 Torr. However, a time-dependent reduction in the gain has been observed with these experimental plates because of the accumulation of charge on the insulating strips which are inserted in the wall of the microchannel to establish the angled electrostatic field.

Proportional counter with automatic gain control

In aid of solar X-ray experiment aboard the earth satellite ESRO-II a proportional counter was developed, at the Utrecht Space Research Laboratory, of which the gas gain can be monitored. There are different factors that can influence the gas gain of a proportional counter, of these the gas pressure and supply voltage are the most important. This paper describes the electronic circuitry that makes use of this monitor voltage to control the high voltage supply of the proportional counter so that a constant output pulse height distribution of the X-ray detector can be achieved.

Basic Properties of Electron Multiplier Ion Detection and Pulse Counting Methods in Mass Spectrometry

The critical role played by first stage gain in shaping the output pulse height distribution and detection efficiency of an electron multiplier used as an ion detector is studied theoretically and experimentally. In a well-focused electron multiplier it is found that anode pulse height distributions observed for different ion species agree well with distributions calculated by using compound Poisson statistics. Models are developed to explain measurement bias in an electron multiplier which is used in either the dc or pulse counting modes and it is shown how these results can be applied to isotope ratio measurements. Design and operating characteristics are described for a 20 stage electron multiplier which was developed for high speed pulse counting and high detection efficiency. The surface of the first dynode is coated with a thin film of Al2O3 to provide a stable first stage yield of 7–9 secondary electrons/incident ion for monatomic alkali ions with 20 kV impact energy. The polyatomic ion Na2BO2+ yields about 16 secondary electrons/incident ion at 20 kV impact energy. Resolving time of the entire detector system is reduced to 10 nsec by using a specially designed solid state discriminator and pulse shaper. Also, a technique is described for the simultaneous detection and pulse counting of two ion beams.

Multiplier Phototubes for Single Electron Counting

Typical operating characteristics of ITT Industrial Laboratories' special purpose multiplier phototubes are described, with particular emphasis on the ability of these tubes to count single photoelectrons with minimum interference from dark noise. This ability, of particular significance in the detection of low energy quanta, including single photons, follows from the Poisson-like output pulse height distribution observed in the tubes in which a well-defined most probable pulse amplitude appears, compared to a more complex but lower amplitude dark noise pulse height spectrum. Other features of these tubes, such as adjustable cathode size and shape, electrical deflection for automatic gain calibration, alignment and image tracking, and reduction of dark noise with cooling, are also described.