Pulse Height Distribution Curve Research Articles

Properties of photon counting imaging system with Si thin films

The Si thin films on ceramic substrates,which were fabricated by electron beam evaporation,were applied as charge induction layers in photon counting imaging system with induction readout. The structures and micrograph of Si thin films were studied. The X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FESEM) images indicate that the thin film has amorphous structure and is coarse due to the lattice boundary of ceramic substrate. The experimental setup was established and the detector resolution,counting rate,pulse height distribution curves etc., with different Si film thickness were compared. The results suggest that the film thickness influences on spatial resolution less than on the counting rate. Moreover,the properties of the system with Si and Ge thin films of the same resistance were compared,which shows that the properties such as distortion,counting rate and dark count rate are better with the Si films.

An ultraviolet photon counting imaging detector system based on Ge induction readout mode

Photon counting imaging technology has been widely used in nuclear radiation detection, space environment detection, astronomy observation, nuclear physics and ultraweak bioluminescence. The structure and operating principles of ultraviolet photon counting imaging systems based on direct electron collection mode and induction readout mode are introduced, but there are more advantages with the induction readout mode. The gain characteristic, resolution, linearity and count rate of a system based on induction mode are evaluated. The dark count pulse height distribution curves shift towards higher pulse height, and the dark count rate increases as the voltage increases. The pulse height distribution curves with light incidence also indicate that the count rate with higher pulse height increases as the voltage increases. The resolution test results show that the system resolution is better than 100 μm along the Y direction and better than 80 μm in some areas. The nonlinearity in both directions is less than 5% in a Φ35 mm area. The system resolution at a low count rate is better than that at a high count rate.

Analysis of cold rolled steels of different reduction ratio using the magnetic Barkhausen noise technique

Magnetic Barkhausen Noise (MBN) was used to evaluate the magnetic behaviour of nuclear reactor pressure vessel steel specimens cold rolled to reduction ratios between 0% and 60%. Measurements performed at increasing reduction ratios revealed variations in the angular dependence of a parameter termed ‘MBNenergy’, concurrent with modifications in the shape of the pulse height distribution curves. The angular preference of MBNenergy present prior to cold rolling was destroyed at intermediate reduction ratios (≈25%), and restored with further reduction (≈40%). Along the rolling direction, the number of large voltage pulses was reduced at reduction ratios of ≈25%, increasing again at ≈60% reduction ratio. Results were attributed to competing effects between crystallographic texture, microscopic and macroscopic residual stresses.

An ultrasoft x-ray fluorescence detector for EXAFS measurements on low-Z elements

An ultrahigh vacuum compatible x-ray detector has been developed for measuring the extended x-ray absorption fine structure (EXAFS) of low-Z elements (C,N,O) by fluorescence yield detection. The detector is a type of gas scintillation proportional counter, with a better energy resolution than conventional gas proportional counters. Two Mylar windows of 0.6 μm thickness and 36 mm diameter in series, in combination with a differential pumping system, were utilized for the entrance of ultrasoft x-ray fluorescence. The energy resolution (full width half maximum) of 46% at 183 eV was confirmed by measuring the boron Kα pulse height distribution curve. Fluorescence yield EXAFS spectra, with high signal-to-background ratios, were obtained above O and N K edges of thin SiO2 and Si3N4 films for the first time by using this detector. These results demonstrate that the newly developed detector with improved energy resolution is extremely useful for fluorescence yield EXAFS measurements of low-Z atoms on the surface and in the bulk.

The Channel Electron Multiplier as an Alpha Detector

The response of Bendix CEM 401 channel electron multipliers to a hot filament electron source and a 244Cm alpha source has been investigated. This investigation shows that a CEM operated in the saturated mode produces output pulses for alpha particles which are, on the average, about twice the height of those for single electrons. A series of pulse height distribution curves obtained with various alpha absorbers and electric field potentials between the source and CEM are presented to substantiate this conclusion.

Gas Flow Proportional Counter for Electron Probe Light Element Analysis

A gas flow proportional counter designed for use as the detector in a microprobe nondispersive system is described. The counter design incorporates (1) relatively low operating voltage with high multiplication factor, (2) an anode wire support to minimize ``end effects'' on the pulse height distribution curve, and (3) an over-all design to permit convenient disassembly and replacement of the anode wire or other components. Results of performance studies indicate higher resolving power than similar commercial counters and negligible shift in multiplication factor over a wide range of counting rates.

A proportional counter tube for X-ray diffraction analysis

An argon-filled, ethyl alcohol quenched counter utilizing a diagonal radiation absorption path is described. The quantum efficiency is 67% when detecting CuKα quanta. When it is used in conjunction with a single-channel pulse amplitude analyser operating with a bandwidth of 3 6 V centred at 30 V its overall efficiency is 46%. Little distortion is introduced into the pulse height distribution curve owing to the incomplete dissipation of the energy of the photoelectrons, and the required low capacitance for high signal-to-noise ratios at low operating potentials is preserved.

Low energy measurements with the photomultiplier scintillation counter

The method of statistical generating functions is used to investigate the process of cascade multiplication. The equations developed are used to examine the nature of the pulse height distribution curve from the scintillation counter and to evaluate the counting efficiency of this instrument. It is found that the maximum of the distribution may be displaced considerably from the position of the mean and curves are drawn to illustrate this. The effects of non-uniform photocathode and dynode surfaces are investigated and it is concluded that these have little influence compared with the normal statistical processes.

Scintillation Spectrometer Studies on the Decay Schemes of Silver-110, Antimony-124 and Iodine-131

IN order to study the decay schemes of radio-isotopes, we have used two scintillation spectrometers in coincidence. The construction of the spectrometers used and the measuring technique have been described earlier1. The pulses from one of the spectrometers are analysed by a single-channel pulse analyser. Pulses corresponding to a certain energy-range are selected by the channel, and the output pulses from the analyser are fed to the sweep-trigger of an oscilloscope. The pulses from the second spectrometer are led to the vertical deflexion plates of the oscilloscope. Only pulses which are in coincidence with those selected by the pulse analyser then appear on the screen. The coincidence-rate is 10–100 pulses per minute. The screen is photographed for a few hours. A picture of the pulse–height distribution is then obtained on the photographic plate; the density at a particular point is a measure of the number of pulses with the corresponding height. The density is determined by means of a microphotometer, and, from the known density curve of the plate, one obtains the pulse–height distribution curve. With the pulse analyser one thus selects pulses corresponding to a certain beta- or gamma-ray energy, and from the shape of the coincidence spectrum obtained one can infer what gamma-rays are in coincidence with the selected radiation.

IONIZING POWER OF COSMIC RAY PARTICLES AT SEA LEVEL

Using a proportional counter telescope arrangement, experiments have been carried out at sea level to explore the nature and ionizing power of particles in the soft component of cosmic radiation and those produced under 1.8 cm. and 20 cm. of lead. The results indicate a preponderance of relativistic electrons in the soft component and under 20 cm. of lead. Under 1.8 cm. of lead there is some disagreement with the calculated pulse height distribution curve but this can be attributed to the production of showers in the lead. These showers would obscure the presence of a small number of particles of unusually high ionizing power, if such exist.

Pulse Height Analyzer

In nuclear experiments where conditions may change rapidly it is desirable to obtain simultaneously a number of points on the pulse height distribution curve, which is a plot of the number of particles given off in the experiment versus their energy.