Alpha Detector Research Articles

The limitations of associated alpha particle technique for contraband container inspections

Inspection of a shipping container for the presence of the threat materials has been investigated in the laboratory by using a 14MeV neutron beam, a BaF2 gamma detector and the associated alpha particle technique. The associated alpha particle technique is proposed as a part of a two sensor system for contraband container inspections. This method is effective in the reduction of background radiation with the possibility of collimating electronically the neutron beam.The intrinsic time resolution has been experimentally estimated to be 1.3ns (FWHM), which allows inspection of a minimum voxel having 7cm depth along the neutron flight path. The neutron beam intensity plays a crucial role as a limiting factor for the acquisition time reduction. Single counting rates of the gamma and alpha detector were investigated as a function of the neutron intensity, distance between the gamma detector and the neutron source and the type of shielding. The time and the energy spectra for different neutron intensities were evaluated.

Simultaneous determination of 222Rn and 220Rn exhalation rates from building materials used in Central Italy with accumulation chambers and a continuous solid state alpha detector: Influence of particle size, humidity and precursors concentration

A method to determine simultaneously the rates of 222Rn and 220Rn released from building materials quarried in Central Italy is presented. The method makes use of a continuous monitor equipped with a solid state alpha detector, in-line connected to a small accumulation chamber. The effects of chamber leakage and back diffusion on 222Rn free exhalation rate is evaluated. The influence of available exhalation surface, humidity content and precursors concentration on radon and thoron exhalation rates is investigated.

Fast coincidence counting with active inspection systems

This paper describes 2nd and 3rd order time coincidence distributions measurements with a GHz processor that synchronously samples 5 or 10 channels of data from radiation detectors near fissile material. On-line, time coincidence distributions are measured between detectors or between detectors and an external stimulating source. Detector-to-detector correlations are useful for passive measurements also. The processor also measures the number of times n pulses occur in a selectable time window and compares this multiplet distribution to a Poisson distribution as a method of determining the occurrence of fission. The detectors respond to radiation emitted in the fission process induced internally by inherent sources or by external sources such as LINACS, DT generators either pulsed or steady state with alpha detectors, etc. Data can be acquired from prompt emission during the source pulse, prompt emissions immediately after the source pulse, or delayed emissions between source pulses. These types of time coincidence measurements (occurring on the time scale of the fission chain multiplication processes for nuclear weapons grade U and Pu) are useful for determining the presence of these fissile materials and quantifying the amount, and are useful for counter terrorism and nuclear material control and accountability. This paper presents the results for a variety of measurements.

Calibration of the Mars Pathfinder alpha proton X‐ray spectrometer

The chemical compositions of Martian rocks and soils examined with the alpha proton X‐ray spectrometer (APXS) during the Mars Pathfinder 1997 lander mission were not previously fully determined. Preliminary chemical results included major element abundances determined by the incomplete calibration of the X‐ray mode. The data collected from the alpha and proton detectors were not previously analyzed due to significant atmospheric contributions to the spectra. The backup instrument of the Pathfinder alpha proton X‐ray spectrometer flight instrument has been used to complete the instrument calibration under simulated Martian conditions at the University of Chicago. An APXS instrument has been used to create a Pathfinder calibration library to test the accuracy of all three instrument modes under simulated Martian conditions. This calibration library has been tested on a number of geologic standards. We have also corrected for instrument differences between the laboratory and flight units. Significant chemical results, somewhat different from those initially reported by Rieder et al. [1997a] and by Wänke et al. [2001], are reported by Foley et al. [2003] as a result of this reanalysis of the Pathfinder APXS data.

Development of a flow-cell alpha detector utilizing microencapsulated CsI:Tl granules and silicon PIN-photodiodes

A flow-cell detector was developed utilizing microencapsulated granular CsI:Tl and silicon PIN-photodiodes for gross alpha radiation quantification. The CsI:Tl scintillator was crushed and sieved to 63-90 and 90-125 /spl mu/m particle size and encapsulated with 10% (ratio of coating layer mass to particle mass) of parylene C polymer. The radiation detector consisted of a CsI:Tl flow-cell and two silicon PIN-photodiodes (PDs). Signals from the PDs were processed by charge-sensitive preamplifiers and shaping amplifiers, then digitized by a GaGe CompuScope 8012 A/PCI 12-bit dual-channel 50-MHz digital oscilloscope card residing in a Pentium III 450-MHz PC. The digitized signal was processed by a LabVIEW-based data-acquisition program for pulse-height and pulse-shape analyses in conjunction with a software-realized coincidence mode with a resolving time of 800 ns. By setting an appropriate region of interest (ROI) for alpha events in a dual parameter histogram, the spillover of beta events into alpha ROI was less than 3.9%. The initial detection efficiency for /sup 233/U was 8.8-19.5% and declined with time due to aqueous solution diffusing through the microencapsulant. The initial detection efficiency decreased with increased particle size, increased porosity, and increased contact time. The slow component of the detection efficiency "half-life" was measured to be 36 h when 1000 Bq mL/sup -1/ /sup 233/U in 0.1 HNO/sub 3/ solution circulated in a closed loop through the flow-cell at a flow rate of 1.0 ml min/sup -1/. The alpha minimum detectable concentration of a CsI:Tl flow-cell with approximate active volume of 0.075 ml was measured to be 12.4 Bq mL/sup -1/ for a 120-s count time.

Fuzzy detection of EEG alpha without amplitude thresholding

Intelligent automated systems are needed to assist the tedious visual analysis of polygraphic recordings. Most systems need detection of different electroencephalogram (EEG) waveforms. The problem in automated detection of alpha activity is the large inter-individual variability of its amplitude and duration. In this work, a fuzzy reasoning based method for the detection of alpha activity was designed and tested using a total of 32 recordings from seven different subjects. Intelligence of the method was distributed to features extracted and the way they were combined. The ranges of the fuzzy rules were determined based on feature statistics. The advantage of the detector is that no alpha amplitude threshold needs to be selected. The performance of the alpha detector was assessed with receiver operating characteristic (ROC) curves. When the true positive rate was 94.2%, the false positive rate was 9.2%, which indicates good performance in sleep EEG analysis.

Innovative characterization, monitoring and sensor technologies for environmental radioactivity at USDOE sites

The mission of the U. S. Department of Energy Office of EnvironmentalManagement (EM) is to clean up its contaminated sites from the past productionof nuclear weapons. Within EM, the Office of Science and Technology (OST)is responsible for providing a full range of science and technology resourcesneeded to support resolution of EM cleanup and long-term environmental stewardshipproblems. This responsibility includes implementation of a technology developmentpathway from basic research to development, demonstration, and deploymentof scientific and technological solutions needed by DOE sites. One OST Programis the Characterization, Monitoring, and Sensor Technology Crosscutting Program(CMST-CP), which aims to provide innovative technologies (i.e., faster, better,cheaper, and/or safer) for environmental characterization and monitoring.This paper describes several technologies that CMST-CP has supported for developmentwith significant benefits realized or projected over the baseline characterizationand monitoring practices. Examples of these technologies include mapping ofsubsurface radioactivity using Cone Penetrometer and drilling techniques;a Rapid Liquid Sampler for Sr, Ra, Tc, and Cs using 3M Empore™ Rad Disks;Long-Range Alpha Detectors; a Compact High Resolution Spectrometer; BetaScint™for determination of Sr in soil; Laser-Induced Fluorescence Imaging techniquesfor mapping U on surfaces; the Environmental Measurements While Drilling System;and the Expedited Site Characterization methodology.

A compact multiparameter acquisition system for radon concentration studies

A compact device suitable to acquire and display, at the same time, radon concentrations in a given atmosphere, and the environmental parameters characterising the atmosphere, is presented and described. It consists of two main blocks: (i) a detection section including a set of sensors for measuring pressure, humidity and temperature, and a set of silicon surface barrier detectors mounted in electrostatic cells collecting the ionised radon daughters; (ii) a single NIM module featuring an eight channel 12 bit ADC and the linear electronics to shape the signals from the silicon detectors. The system is controlled by a computer via a RS232 port. The software, implemented in Visual Basic, allows to display the energy distribution of the pulses coming from the alpha detectors and to initialise and control all phases of the acquisition. The results of preliminary tests show the high reliability of the system.

Analyses of Diagnostic Failure Effect and Fail-Safe Ignited Operation in a Tokamak Fusion Reactor

The consequence of the failure effect of burn control diagnostic systems, such as neutron diagnostics, bolometers, electron cyclotron emission power loss diagnostics, interferometer, and lost alpha detector, on ignited operation has been analyzed, and the fail-safe operation in a tokamak fusion reactor including the International Thermonuclear Experimental Reactor (ITER) has been considered. Because the failure of the neutron diagnostic system for fusion power measurement leads to a fusion power surge for the simple control algorithm, the fail-safe control algorithm has been introduced to avoid this problem. As failure of the power loss measurement such as the bolometer system terminates the ignition, then it is less problematic. The effect of the interferometer fringe counting error on the ignited operation is not simple, as just mentioned, and a lost alpha detector can be removed from the feedback system using the preset value.

The GT resonance revealed in β+-decay using new experimental techniques

The GT beta decay of 150Ho has been studied with a Total Absorption Spectrometer (TAS), with an array of 6 Euroball CLUSTER Ge detectors (the CLUSTER CUBE), and with an alpha detector. The three techniques complement each other. The results provide the first observation of an extremely sharp resonance in GT beta decay.

Alpha particle absorption and inclined incidence track parameters evaluation in plastic detectors

Abstract In this work the use of our recently constructed irradiation chamber was involved in the current experiments. The absorption of alpha particle in air has been studied through a set of experiments in which the stopping power has been measured. A comparison between the calculated values and the present experimental results is given and a good agreement has been found. Critical angle ( θ c ) determination has been carried out using two different techniques, via indirect and direct measurements, under different etching conditions and at various alpha energies. An empirical fit of θ c − h ( h is the removal thickness layer) dependence has been calculated and found to work well in the studied h ranges. Also, the inclined alpha tracks parameters of energies between 1.0 and 5.0 MeV have been studied. Results can be successfully applicable in alpha autoradiography studies and detector efficiency determination for track registration in plastic recorders.

Thin film diamond alpha detectors for dosimetry applications

Abstract Diamond is a resilient material with rather extreme electronic properties. As such it is an interesting candidate for the fabrication of high performance solid state particle detectors. However, the commercially accessible form of diamond, grown by chemical vapour deposition (CVD) methods, is polycrystalline in nature and often displays rather poor electrical characteristics. This paper considers the way that this material may be used to form alpha particle dosimeters with useful performance levels. One approach adopted has been to reduce the impurity levels within the feed-stock gases that are used to grow the diamond films. This has enabled significant improvements to be achieved in the mean carrier drift distance within the films leading alpha detectors with up to 40% collection efficiencies. An alternative approach explored is the use of planar device geometry whereby charge collection is limited to the top surface of the diamond which comprises higher quality material than the bulk of the film. This has lead to collection efficiencies of greater than 70%, the highest yet reported for polycrystalline CVD material based detectors. Techniques for improving the characteristics of these devices further are discussed.

A position-sensitive alpha detector using a thin plastic scintillator combined with a position-sensitive photomultiplier tube

A position-sensitive alpha detector was developed and tested. The alpha detector consists of a thin plastic scintillator, a position-sensitive photomultiplier tube, a position calculation circuit and a personal computer based data acquisition system. Because the thin plastic scintillator has high-detection efficiency for alpha particles while it has low-sensitivity for beta particles or gamma ray, the detector can selectively detect alpha particles with low background counts. The spatial resolution of the detector was approximately 3 mm FWHM. An autoradiographic images of plutonium distribution in the lung of an animal as well as an image of an uranium particle were successively obtained. Spatial and energy distribution of radon daughters could also be measured. We conclude that the developed position-sensitive alpha detector is useful for some applications such as plutonium detection or alpha autoradiography as well as distribution analysis of radon daughters.

Observation of the trapping of radioactive inert gas radon on oxide glass surfaces: Macroporous scintillating-glass-fiber bundler alpha detector

We report the observation of the trapping of radioactive inert gas radon ( 222Rn) on oxide glass under ambient air temperature and pressure of 300 K and 760 Torr, respectively. Radon diffuses from the source, through two macroporous scintillating-glass-fiber bundle alpha detectors in series, to the end of the linear closed system filled with ambient air. The strategy is to provide radon atoms and alphas emitted from radon and its progeny with large accessible scintillating glass surface areas for efficient trapping and detection, respectively. Diffusion-only transport mechanism could not explain the experimental observations, strongly suggesting the trapping of radioactive inert gas radon ( 222Rn) on oxide glass.

High Collection Efficiency Thin Film Diamond Particle Detectors

AbstractDiamond is a resilient material with rather extreme electronic properties. As such it is an interesting candidate for the fabrication of high performance solid state particle detectors. However, the commercially accessible form of diamond, grown by chemical vapour deposition (CVD) methods, is polycrystalline in nature and often displays rather poor electrical characteristics. This paper considers ways in which this material may be used to form alpha particle detectors with useful performance levels. One approach adopted has been to reduce the impurity levels within the feed-stock gases that are used to grow the diamond films. This has enabled significant improvements to be achieved in the mean carrier drift distance within the films leading to alpha detectors with up to 40% collection efficiencies. An alternative approach explored is the use of planar device geometries whereby charge collection is limited to the top surface of the diamond which comprises higher quality material than the bulk of the film. This has lead to collection efficiencies of 70%, the highest yet reported for polycrystalline CVD diamond based detectors. Techniques for improving the characteristics of these devices further are discussed.

Polycarbonate Track Etched Detectors for Qualitative Alpha Spectroscopy in Radon Environments

Using the optimised two-step ECE technique, various alpha energy windows may be generated which vary in widths from 0.8 MeV to 7 MeV and the lowest detectable alpha energy may be shifted from 0.5 MeV to 8 MeV. By shifting alpha energy windows of minimum width over the energy range, qualitative alpha spectra of radon and radon daughters have been investigated using bare detectors and detectors inside the Karlsruhe radon diffusion chamber. These spectra have been found to differ from those of the semiconductor detector mainly due to the critical angle of alpha detector in Makrofol DE. The actual alpha energy windows for various etching regimes applied for the FZK radon diffusion chamber in different laboratories are compared with that of a new optimised one using a window of 4.5 MeV. This results in a factor of 3 higher radon response and a smaller coefficient of variation. In addition, an alpha energy window has been optimised for a bare PC detector which allows for the measurement of 214Po in air by discriminating the plateout effects on the detector surface.

Foil deposition alpha collector probe for TFTR’s D-T phase

A new foil deposition alpha collector sample probe has been developed for TFTR’s D-T phase. D-T fusion produced alpha particles escaping from the plasma are implanted in nickel foils located in a series of collimating ports on the detector. The nickel foils are removed from the tokamak after exposure to one or more plasma discharges and analyzed for helium content. This detector is intended to provide improved alpha particle energy resolution and pitch angle coverage over existing lost alpha detectors, and to provide an absolutely calibrated cross-check with these detectors. The ability to resolve between separate energy components of alpha particle loss is estimated to be ∼20%. A full 360° of pitch angle coverage is provided for by eight channels having an acceptance range of ∼53° per channel. These detectors will be useful in characterizing classical and anomalous alpha losses and any collective alpha instabilities that may be excited during the D-T campaign of TFTR.

Long-range alpha detector sample monitoring

Long-range alpha detector (LRAD) systems are designed to monitor alpha sources and contamination by measuring the number of ions created in air by ionizing radiation. Traditional alpha detectors are designed to detect alpha particles directly and must be passed slowly within about 3 cm of an alpha source to operate effectively. LRAD detectors collect the ions created from alpha interactions with air. Therefore, they are better able to monitor equipment and complex surfaces and can be operated at a much greater distance from an alpha source than traditional alpha detectors. Furthermore, because LRAD detectors remain stationary during monitoring, they are less subject to operator error than traditional alpha detectors. This paper will discuss the basic operation as well as recent advances that have been made to LRAD Sample Monitors.

Long-range alpha detector (LRAD) sensitivity to beta contamination and soil moisture

Long-range alpha detector (LRAD) systems are designed to monitor alpha contamination by measuring the ionization in air formed by the alphas. Recent tests have been performed to determine the sensitivity of LRAD systems to beta contamination and soil moisture levels. These results and the general technology are discussed in this paper.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radiation Physics with Applications in Medicine and Biology

Interactions between radiation and matter nuclear reactions and the production of radioisotopes instrumentation - an introduction to alpha, beta and gamma radiation detectors the radiation from nuclear decay applications of radioisotopes in medicine and biology neutrons in biology and clinical medicine other accelerator-based applications in medicine and biology principles of radiation protection.