Pulse Height Measurements Research Articles

Pulse-height measurements with a cooled avalanche-photodiode detector.

A cooled avalanche-photodiode (APD) detector has been developed for X-ray diffraction experiments. Although an APD is normally used at room temperature and a high internal gain, the energy resolution can be improved by decreasing temperature and gain. The APD device was cooled to 253 K by a thermoelectric cooler. When the gain was M = 13, the energy resolution was 5% (FWHM) at 16.53 keV with a charge-sensitive preamplifier. By scanning the discriminator threshold level of a fast-counting system, energy spectra were obtained at M approximately 50 and count rates of up to 4.7 x 10(7) s(-1).

A fast detector using stacked avalanche photodiodes for x-ray diffraction experiments with synchrotron radiation

We have developed a fast detector using stacked avalanche photodiodes (APDs) for x-ray diffraction experiments with synchrotron radiation. This detector has four independent channels of APDs, and the detector efficiency has reached 55% in all for 16.53 keV x rays. Since the dead time of the counting system is shorter than 4 ns, output rates of up to 4.5×108 counts/s have been obtained for 16.53 keV x rays. The dynamic range is more than 1010 in the multibunch mode of a storage ring. Pulse-height measurements at output rates of up to 108 counts/s were successfully carried out by sequential single-channel discrimination.

Study of localised radiation damage to PIPS detectors by a scanning ion microprobe: Measured effects and the consequences for STIM analysis

Radiation damage effects in a PIPS particle detector have been studied by direct irradiation with a 4 MeV He + focused ion beam, using the Eindhoven scanning ion microprobe set-up. This set-up enables extreme sensitivity and accuracy in pulse-height measurement. Pulse-height dependence on ion dose and the lateral variations of pulse-height response after damaging were studied, for different bias voltages. Pulse height was found to decrease linearly with ion dose and this could be observed after only a few ions per scan position, corresponding to a dose of 10 8/cm 2. Pulse-height loss was found to be restricted to damaged detector areas. Consequences of this pulse-height dependence on ion dose and scan position for the accuracy of STIM analyses are discussed.

Status of the KEDR drift chamber

The 1 m long and 1 m outer diameter KEDR drift chamber consists of 42 layers. The chamber is based on a jet type cell. In addition to drift time measurements, pulse height measurements will provide particle separation by dE dx . The measurements of the spatial resolution and the effects of the end plates on resolution and aging tests were performed using prototypes filled with DME gas. The resolution averaged over the drift distance has a value of 40 μm. The relative gain drop is equal to 45 %/(C/cm).

Digital techniques for real-time pulse shaping in radiation measurements

Recursive algorithms for real-time digital pulse shaping in pulse height measurements have been developed. The differentiated signal from the preamplifier (exponential pulse) is amplified and then digitized. Digital data are deconvolved so that the response of the high-pass network is eliminated. The deconvolved pulse is processed by a time-invariant digital filter which allows trapezoidal/triangular or cusp-like shapes to be synthesized. A prototype of a digital trapezoidal processor was built which is capable of sampling and processing digital data in real time at clock rates up to 50 MHz.

Evidence for field enhanced electron capture by EL2 centers in semi-insulating GaAs and the effect on GaAs radiation detectors

The performance of Schottky contact semiconductor radiation detectors fabricated from semi-insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi-insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi-insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements.

Fission fragment velocities, masses, and energies from 232Th(n, f) in the resonance-energy region

Fragment velocities, masses, and energies from neutron-induced fission of 232Th were measured at various neutron energies in the subthreshold-resonance region around E n ≅ 1.6 MeV and above threshold with good neutron-energy resolution. These quantities were obtained by three different methods using two different types of detectors, namely parallel plate avalanche counters for time of flight, and surface-barrier detectors for time of flight and pulse height measurements. Comparison of the different results and a careful error analysis clearly exhibit the limitation in resolution due to methodical uncertainties. Within these limits, none of the measured quantities shows dependencies on neutron energy.

Ionization energy in an HPGe semiconductor detector

We report measurements of the relative pulse heights produced simultaneously by alpha particles with energies in the range 3.2–5.8 MeV and gamma rays in an hyperpure Ge detector at T = 80 K. From these data, we conclude that the mean energy to create electron-hole pairs is smaller for α's than for γ's i.e. ϵ α < ϵ 0 contrary to earlier conclusions. Specifically, ϵ α / ϵ 0 = 0.9914 ± 0.0010 at E α = 5486 keV. The deviation in the ratio ϵ α/ϵ 0 from unity increases with decreasing α energy.

A fast, versatile single dual-parameter multichannel analyzer

The design of a single dual-parameter multichannel pulse-height analyzer is reported. The analyzer is especially cut out for pulse-height spectrum measurements from high counting rate sources. The instrumentation-peculiar characteristics are as follows: (1) the true acquisition phase is an autonomous one; (2) the analyzer has a count capacity of 2/sup 32/-1 counts/channel, a minimum dead time of 200 ns, and a maximum conversion gain of 2/sup 20/ channels; (3) the measurement points can be grouped in measurement blocks (MBK); (4) the acquired data are transferred from the instrumentation to the computer under interrupt control-several interrupt possibilities are foreseen for the sake of flexibility; and (5) the system is constructed from commercially available components. >

Pulse height response of Si surface barrier detectors to 5–70 MeV heavy ions

An extensive series of pulse height measurements have been performed in partially depleted Si surface barrier detectors, using various heavy ions (Li, B, C, O, Al and Cl), at energies between 5 and 70 MeV. After correcting for the small energy loss of the incident ions in traversing the gold surface barrier layer of the detector and for the residual nuclear stopping, the resulting pulse heights per MeV for the various heavy ions were found to be up to 2.5% larger than for the 241Am (5.486 MeV) alpha particle. This increase, although significant, is smaller than had been anticipated from an extrapolation of the earlier study of H, He and Li pulse heights by Lennard et al. [Nucl. Instr. and Meth. A248 (1986) 454, and B24/25 (1987) 1035.] A new method of analysis of pulse height data, which significantly reduces the uncertainties associated with the dead layer energy loss and nuclear stopping corrections, was used in order to determine directly the variation of the average energy for electron-hole pair creation with increasing particle stopping power in Si. The dependence of the detector energy resolution (FWHM) on the energy and atomic number of the particle has also been measured in order to provide a suitable data base for selecting the optimum ion beams for various backscattering analysis problems.

A digital preprocessor for multiparameter experiments

In conventional two- or more-dimensional pulse height measurements, two or more ADCs or similar data sources are connected to a histogramming memory via a router module. A software configurable signal-processor-based router with extended features is described.

Anomalous pulse heights in silicon detectors

Accurate measurements of the relative pulse heights produced by alpha particles from radioactive sources (148Gd and 241Am) in a silicon surface-barrier detector show that the detector response is not linear in the deposited energy. A semi-empirical model, wherein the average energy to create an electron-hole pair in Si is dependent on the energy loss rate of the ionizing particle, is in fair agreement with the experimental data.

Development of the CRID single-electron wire detector

We describe the R&D effort to define the design parameters, method of construction and experimental results of single-electron wire detectors. These detectors will be used for particle identification using Cherenkov ring-imaging techniques in the SLD experiment at SLAC. We present measurements of pulse heights for several gases as a function of gas gain, charge division performance on a single-electron signal using both 7 and 33 μm diameter carbon wires, photon feedback in TMAE-laden gas, average pulse shape, and its comparison with the predicted shape and cross-talk. In addition, we present results of wire aging tests and other tests associated with construction of this unusual type of wire chamber.

Radial wire drift chambers for the H1 forward track detector at HERA: design, construction and performance

The Forward Track Detector (FTD) in the H1 experiment at the HERA electron-proton collider includes three large radial wire drift chambers for accurate charged track reconstruction and particle identification. The chambers achieve the simultaneous requirements of good space point determination and good pulse height measurement. The latter is exploited for enhanced electron/hadron discrimination using X-ray emission from a transition radiator which precedes each chamber. The design, assembly and operating characteristics of the chambers are described.

Progress report on Cerenkov ring imaging detector development

The authors present recent progress on the construction and testing of the first drift boxes and single-electron detectors as they come from the production line. These detectors will be used for particle identification using the ring imaging technique in the SLD (Standard Linear Collider Large Detector) experiment. Various experimental results are presented, including single-electron pulse height measurements as a function of gas gain, detector gating capability, uniformity of response across the wire plane, charge division performance of a single-electron signal, average pulse shape and its comparison with predicted shape, and crosstalk. >

A model for electron/ion recombination in ionization chambers

The recombination of free electrons and positive ions along charged particle tracks in gases has been modeled using electron transport equations which assume homogeneous distributions in the vicinity of the tracks. The equations include space charge terms, which have been neglected in previous models. A formula for the electron yield as a function of detector applied potential is obtained from a perturbation solution valid when the ratio of the Debye length to the charge column radius is larger than unity. When this ratio is very large, the formula reduces to that of previous models. Pulse height measurements in a 3He ionization chamber indicate 2% to 30% losses to recombination which vary with applied field, particle type, and energy. Using reasonable values for the electron transport coefficients, the calculated loss of signal to recombination is generally in agreement with experiment, but the variation with applied bias is stronger in the experiment.

A LED monitoring system for pulse height and time measurement with scintillation counters

We have developed an on-line LED monitoring system for the scintillation counters of the experiment PHOENICS at the 3.5 GeV electron stretcher ring ELSA in Bonn. The LED light output proved to be stable within 0.3% concerning pulse height and within 15 ps concerning deviation in time measurement. Usually discussed disadvantages of LEDs like temperature dependence, ageing and the bad spectral match with the photomultiplier sensitivity were checked and are well under control.

The new drift chamber for the Mark II detector at the SLAC linear collider

A new central drift chamber has been constructed for the Mark II detector for use the new SLAC Linear Collider. The design of the new chamber is based on a multi-sense-wire cell of the jet-chamber type. In addition to driftime measurements, pulse-height measurements from the sense wires provide electron-hadron separation by d E/d x. The chamber has been installed in the detector and is being at PEP before being moved to the SLC. The design and construction of the chamber, as well as initial performance results from the PEP data, are presented.

A sample-hold and analog multiplexer for multidetector systems

A new sample-hold circuit with an analog multiplexer system is described. Designed for multichannel acquisition of data from an air shower array, the system is being used for accurate measurements of pulse heights from 16 channels by the use of a single ADC.

A multistep parallax-free X-ray imaging counter

Abstract With a large preamplifying gap of 2 cm, combined with a localization multiwire chamber, it is shown that measurement of pulse height provides the depth of the atom which absorbs a monoenergetic low-energy X quantum to a great accuracy. The preliminary results show that for 8 keV X-rays, accuracies of a fraction of a millimetre are achieved. No error is introduced by the limited efficiency of the absorbing gap, thus permitting the use of low-cost argon mixture fillings. Large-surface parallax-free gaseous detectors of planar structure can be built for monoenergetic diverging sources.