Large Pulse Height Research Articles

Efficient Alpha Radiation Detector using Low Temperature Hydrothermally Grown ZnO:Ga Nanorod Scintillator

We report efficient detection of alpha radiation on highly textured and vertically aligned along (002) Gallium-doped Zinc Oxide (ZnO:Ga) nanorods on a glass substrate with an average diameter ~150 ± 10 nm. Photoluminescence measurement showed near band emission 393 nm, in agreement with the bandgap value ~3.22 eV, measured by UV-Vis spectroscopy. The developed ZnO:Ga nanorod scintillator is coupled with a commercially available photomultiplier tube and 1K Multichannel Analyser to fabricate an alpha radiation detector. The performance of the alpha radiation detector is evaluated using various activities alpha radiation sources. A large pulse height spectrum is recorded by the detector for different alpha sources against the background spectrum. The calculated detection efficiency and Minimum Detectable Activity (MDA) showed that the detector is highly sensitive to alpha radiation. The repeatability and reproducibility of the performance are studied by evaluating the response of a single scintillator for numerous exposures and by studying inter-batch response variations, respectively. The response is repeatable within ±1% whereas reproducibility varies from ±20% for extremely low activity alpha sources to ±5% for high activity alpha sources. The performance of ZnO:Ga nanorod scintillator grown on glass substrate demonstrates that it can be a promising material system for the detection of alpha radiation.

Research on the detuning system of a cooling electron beam for the dielectronic recombination experiment at CSRm

A storage ring equipped with an electron cooler is an ideal platform for dielectronic recombination (DR) experiments. In order to fulfill the requirement of DR measurements at the main Cooler Storage Ring, a detuning system for the precision control of the relative energy between the ion beam and the electron beam has been installed on the electron cooler device. The test run using 7.0 MeV/u C6+ beam was performed with recording the Schottky spectra and the ion beam currents. The influence of pulse heights and widths of the detuning voltage on the ion beam was analyzed. For the small pulse height, the experimental results from the Schottky spectra were in good agreement with the theoretical results. The frequency shift in the Schottky spectra was significantly reduced for the short pulse width. For the large pulse height, an oscillation phenomenon was observed and some effective ways to reduce the oscillation were pointed out. The detailed description of the phenomenon and the theoretical model based on the plasma oscillation is discussed in this paper. The overall results show that the new detuning system works properly, and could fulfill the requirements of future DR experiments.

Diamond detectors for fast neutron measurements at pulsed spallation sources

The performance of a single crystal diamond (4.7x4.7x0.5mm3 active volume) detector was tested in the ISIS pulsed neutron beam using biparametric (time of flight and pulse height) data acquisition. Three characteristic regions in the biparametric spectra are observed: i) low pulse height events with very short time of flight induced by γ-rays; ii) low pulse height events at longer flight times (i.e. neutron energies En > 3.5–6 MeV), possibly due to neutron elastic scattering off 12C; iii) events with large pulse height and flight times corresponding to En > 6 MeV mainly due to inelastic reactions such as 12C(n,α)9Be and 12C(n,n')3α. The potential use of this detector is discussed in relation to the ChipIr neutron beam line for fast neutron irradiation of electronic components at the ISIS spallation source.

A bismuth activation counter for high sensitivity pulsed 14 MeV neutrons

We have built a fast neutron bismuth activation counter that measures activation counts from pulsed 14-MeV neutron generators for incident neutron fluences between 30 and 300neutrons/cm2 at 15.2cm (6in.). The activation counter consists of a large bismuth germanate (BGO) detector surrounded by a bismuth metal shield in front of and concentric with the cylindrical detector housing. The 14MeV neutrons activate the 2.6-millisecond (ms) isomer in the shield and the detector by the reaction 209Bi (n,2nγ) 208mBi. The use of millisecond isomers and activation counting times minimizes the background from other activated materials and the environment. In addition to activation, the bismuth metal shields against other outside radiation sources. We have tested the bismuth activation counter, simultaneously, with two data acquisition systems (DASs) and both give similar results. The two-dimensional (2D) DAS and three dimensional (3D) DAS both consist of pulse height analysis (PHA) systems that can be used to discriminate against gamma radiations below 300keV photon energy, so that the detector can be used strictly as a counter. If the counting time is restricted to less than 25ms after the neutron pulse, there are less than 10 counts of background for single pulse operation in all our operational environments tested so far. High-fluence neutron generator operations are restricted by large dead times and pulse height saturation. When we operate our 3D DAS PHA system in list mode acquisition (LIST), real-time corrections to dead time or live time can be made on the scale of 1ms time windows or dwell times. The live time correction is consistent with nonparalyzable models for dead time of 1.0±0.2μs for our 3D DAS and 1.5±0.3μs for our 2D DAS dominated by our fixed time width analog to digital converters (ADCs). With the same solid angle, we have shown that the bismuth activation counter has a factor of 4 increase in sensitivity over our lead activation counter, because of higher counts and negligible backgrounds.

Applications and new developments in resistive plate chambers

Resistive plate chambers are rugged and affordable gas detectors that have found extensive use in high-energy physics (HEP) and astroparticle experiments. The main features of these counters are the very large pulse height, reduced cost per unit area, and good (about 1 ns) time resolution. The field has enjoyed very lively progress in recent years, including the introduction of a new (avalanche) mode of operation, extension of the counting-rate capabilities to levels around 10 MHz/cm/sup 2/, improvement of the time resolution for minimum ionizing particles to 50 ps /spl sigma/, and the achievement of position resolutions of a few tens of micrometers. These new developments have extended the range of REP applications and promise new applications in medical imaging.

Cluster impacts on solids

Polyatomic projectiles, which are now available in a large range of size and of incident energies, allow to deposit in solid samples high energy densities that induce large damage in the bulk of irradiated samples as well as very important emission of matter from the bombarded surfaces. Large secondary ion emission yields as well as total particle emission yields induced by Au n impacts were measured on various targets over a large range of incident energies covering the domain of energy deposited through atomic collisions and electronic excitations. An unexpected yield-energy dependence was observed with a strong maximum of the emission rate at moderate velocities (100–200 keV/atom) which may open promising developments in surface analysis. At higher velocity, it has been shown that the equilibrium charge state of the co-moving atoms of swift clusters in solid targets is significantly reduced by comparison with single atoms at the same velocity. This effect, due to the additional ionisation potential created by the proximity of the cluster constituents, has been investigated with carbon clusters of different size, in a velocity range between 600 keV up to 4 MeV/atom. The spatial distribution of cluster fragments exiting thin carbon targets were also measured with a multi-impact position sensitive detector. Comparison with theoretical simulations demonstrated that the in-target Coulomb explosion is strongly shielded. Large pulse height defects measured in silicon detectors are a direct consequence of the interaction of the spatially correlated atoms in the silicon material. Results on pulse height dependence on cluster size and energy will be presented for 1 and 2 MeV/atom carbon clusters. This set of results, obtained recently by the Orsay group (most of them in collaboration with other groups), illustrates different aspects of cluster collisions and/or transmission in solids.

Dependence of scintillation characteristics in the CsI(Tl) crystal on Tl/sup +/ concentrations under electron and alpha particles excitations

This paper reports the emission spectra, pulse heights, and decay curves of CsI(TI) crystals with a Tl/sup +/ concentration ranging from 10/sup -6/ to 10/sup -2/ mol under electron and alpha particle excitations. Larger pulse heights from the crystals with Tl/sup +/ concentration of more than 10/sup -3/ mol were observed for a higher ionization density of alpha particle excitation compared with those of electron excitation. This enhancement may be explained in terms of the higher scintillation efficiency for higher Tl/sup +/ concentration. Decay curves under electron and alpha particle excitations were compared with the decay curve under pulsed UV excitation. The observed decay curves were explained in terms of the sum of the three energy transfer processes to create excited states (Tl/sup +/)*: the prompt process, the V/sub k/ diffusion process to Tl/sup 0/, and the electron release process from Tl/sup 0/ to Tl/sup ++/. Here, Tl/sup 0/ and Tl/sup ++/ were produced through (Tl/sup +/+electron)/spl rarr/Tl/sup 0/ and [Tl/sup +/+hole (or V/sub k/)]/spl rarr/Tl/sup ++/.

Modeling Square-Wave Voltammetry of Thin Protein Films Using Marcus Theory

A model combining Marcus theory with Gaussian distributions of kinetic and thermodynamic parameters was developed for square-wave voltammetry (SWV) and applied to the protein myoglobin in thin films of didodecyldimethylammonium bromide on electrodes. Nonlinear regression analysis allowed direct estimation of electron transfer rate constants and reorganization energies from single experiments at relatively large pulse heights. Successful fitting relies on the accurate representation of background current within the model. Analysis of 22 voltammograms at pH 6 over a range of frequencies and pulse heights gave a formal potential consistent with earlier determinations, and a mean log( ) of 3.3 + 0.8 s-1, not significantly different from the mean log( ) of 3.0 ± 0.6 s-1. The mean value of reorganization energy λRED was 0.41 ± 0.02 eV and λOX was 0.21 ± 0.01 eV. Differences in λRED and λOX are likely to reflect different solvation, bonding, and conformation near the iron heme regions of MbFeIII and MbFeII. Meth...

The influence of pearlite on Barkhausen noise generation in plain carbon steels

Barkhausen noise refers to the abrupt, discontinuous changes in magnetization which result from domain walls overcoming barriers to their movement. Barkhausen noise is sensitive to a number of parameters, notably stress level (for which it is being examined as a basis for non-destructive evaluation) and microstructure. The present study investigates the influence of pearlite content on the pulse height distribution of the magnetic Barkhausen noise signal in plain carbon steels. The responses of purely pearlitic and purely ferritic microstructures are determined to be quite different. Samples containing no pearlite display a narrow, symmetrical distribution of relatively small pulse heights. The behaviour of the pearlitic steel is quite different, however, exhibiting an asymmetrical pulse height distribution with a significant tail extending to comparatively large pulse heights (approximately four times that of the maximum for the ferrite signal). Steels containing both ferrite and pearlite produce signal distributions between the two extremes, but contain no significant tail and also appear to tend toward larger pulse heights than what would be expected for a purely “composite” distribution. Results are explained in terms of differences in domain wall pinning behaviour between the various microstructures.

Silicon ion interactions measured in the E-810 TPC at the AGS

The tracking detector of AGS Experiment 810 is a three-piece Time Projection Chamber (TPC) which measures all charged tracks in the forward hemisphere of the nucleon-nucleon center of mass system, i. e. forward of 20 degrees in the lab. Each module of the TPC contains twelve rows of short anode wires which give 3-D space points on each track, but no dE/dx information useable for particle identification. The MPS magnet provides a uniform 5 kG field on the TPC volume. The TPC was operated in a beam of 14.6 × A GeV/c silicon ions at the end of June 1989. This talk reports the results of analysis of the gold and copper target data from that run. The trigger was quite simple, requiring a large pulse height in a Čerenkov counter in the incident beam indicating an incident silicon ion, a small pulse height in a scintillation counter centered on the beam behind the TPC corresponding to less ionization than a surviving carbon ion would produce, and a substantial signal in each of two scintillators located above and below the beam just in front of the TPC. The targets were thin, 0.0076 radiation lengths of gold, 0.0089 radiation lengths of copper, to reduce contamination of the events by electron tracks from converted π 0 photons. A cut at multiplicity 50 was used to select more central collisions, yielding 2291 events from the gold sample, 2170 from the copper. This corresponds to cross sections of 0.59 and 0.20 barns, respectively, defining the “central” sample for the charged particle distributions presented here.

A Monte Carlo simulation of the response of a hadronic calorimeter to protons of momentum 3.5 to 200 GeV/c

The response of scintillation counters in an ionization calorimeter to incident protons of momenta 3.5 to 200 GeV/ c was simulated using the CALOR computer code system. Results of the simulation are compared with data taken at Brookhaven National Laboratory for 3.5- and 10-GeV/ c protons and at Fermi National Accelerator Laboratory for 50-, 100- and 278-GeV hadrons. Mechanisms which produce large pulse heights for low-energy incident particles are discussed.

Dependence of position signal on pulse height and gas gain for 3H .BETA.-rays observed with position sensitive proportional counter.

Position information obtained with a charge division type position sensitive proportional counter for 3H β-rays emitted from a point source depends on the pulse height and the gas gain, because the gas gain for each β-ray is influenced by the direction of its track with respect to the anode wire. With the increase of the gas gain, position signals of pulses with large pulse height appear first in a single broad position, and then in two different positions. The reason is that the gas gain for 8-rays making the tracks perpendicular to the anode wire is smaller than that for those parallel to the wire owing to self-induced space charge effect at large gas gain. Consequently, the parallel tracks give the largest pulse height of all. When isobutane is used as counting gas, with the further increase of the gas gain position signals of pulses with large pulse height appear in three different positions and finally in a single position. The final phenomenon in isobutane means that the gas gain for β-rays making t...

Statistics of electron multiplication in proportional counters

Pulse spectra produced by the release of single primary electrons in a proportional counter have been determined for a variety of gas fillings. The spectra were recorded with sufficient statistical accuracy to define their logarithmic derivatives in order to investigate deviations from the approximately exponential distributions. Two main effects were observed: (1) at small pulse heights there may be a reduced number of pulses compared with the exponential distribution if the electron multiplication commences in a region of low field strength; (2) at large pulse heights there may be an excess of pulses owing to the occurrence of secondary successor avalanches initiated by photoelectric effects. A theoretical distribution has been derived which describes both these effects in terms of two parameters, one of which is characteristic of the ionizing efficiency of the electron at the commencement of the multiplication process while the other is a measure of the mean number of successors per avalanche. These parameters have been determined for each of the observed spectra.

Calculation of the pulse-height response of NaI(Tl) scintillation counters

A Monte Carlo calculation to determine the pulse-height response of NaI(Tl) scintillation counters to gamma rays is described. Comparisons of several calculations with ecperiments using 3-in.-dia by 3-in.-high crystals for source energies from 0.32 to 7.48 MeV are presented and show good agreement at large pulse heights. At small pulse heights the calculations underestimate the experimental data and indicate that background radiation can contribute significantly to the experimental results. An extensive series of calculations are reported for a 3-in.-dia by 3-in.-high crystal using monoenergetic, point isotropic sources placed on the crystal axis 10 cm from one end. The source energy ranged from 0.1 to 6.0 MeV in this series of calculations.

``Runaway'' Electrons and Cooperative Phenomena in B-1 Stellarator Discharges

Examination of the temporal distribution, relative intensity, and maximum energy of x-rays above 30 kev emanating from the B-1 stellarator during a pulsed discharge has revealed a number of interesting phenomena. The x-rays are assumed to be produced by ``runaway'' electrons when they strike the wall. Spuriously large pulse heights have been observed. The x-rays abruptly appear early in the discharge, before the Kruskal instability can occur. Depending on the operating conditions, x-rays can be observed at any time during the discharge except when the current is at the Kruskal limiting value. If the longitudinal electric field used for ohmic heating is ``crowbarred,'' x-rays can appear afterwards in copious quantities; furthermore, the discharge current can decay in abrupt steps correlated in time with bursts of x-rays. The hypothesis that the current in these steps is due entirely to runaway electrons is consistent with the data. These observations are taken to be evidence for the existence of cooperative phenomena, or collective motions which can affect both the confinement and the heating of a plasma. In addition, intense nonthermal microwave noise has been detected at times correlated with x-ray emission.