Alpha-particle Spectrometer Research Articles

Alpha particle spectrometry based on the mean grey level and visibility of track etch-pit in CR-39 Nuclear Track Detector

The CR-39 detector is used in this work to present an exceptional technique for alpha-particle spectrometry. This new approach is based on determining the mean grey level and visibility of the alpha particle track etch-pit. The latter is used to discriminate alpha particles of different energies that produce the same track diameter at the same etching time. CR-39 detectors had been irradiated by alpha particles with energies 1, 2, 3, 4, and 5 MeV thereafter are chemically etched in 6.25 M NaOH at 70 °C. At various etching periods, the diameter, the mean grey level, and the visibility of the alpha particle track etch-pit were measured. The findings reveal that for a given alpha particle, the mean grey level rises with the increase of the etching time. Conversely, both the visibility and contrast of alpha particle tracks are deteriorating. The alpha particle track etch-pit of equal diameters results from an alpha particle of different energies having different mean grey levels and visibility. In addition, it is confirmed that the mean grey level and visibility of the alpha particle etch-pit are shown to be correlated with the alpha particle energy at a particular etching time. Finally, the proposed approach is intended to overcome the non-monotonical relationship of diameter to the energy of alpha particle track etch-pit. So, our findings have the potential to broaden the application of CR-39 as an alpha particle spectrometer.

Performance characteristics and validation of alpha particle spectrometers for radiometric analysis of natural and anthropogenic radionuclides of environmental impacts

Alpha spectrometry is one of the greatest nuclear techniques for identification and quantification of α-emitters in the environment due to nuclear fuel cycle operations, nuclear materials and geochemical studies or forensic medicine investigations. This study was conducted to re-evaluate and optimize the factors affecting the performance of a multi-chamber alpha spectrometer (EG&G Ortec) used in our laboratory using an aged α-source of 232U in equilibrium with its decay products. The results shown that the energy calibration within energy window 4–9 MeV has been done using alpha particle emissions of 232U (t1/2.70.6 y) and its decay products with good linear fitting (R2 > 0.999). At a source to detector spacing of 10 mm, the efficiency of the detectors varied between 15 and 20%; while the better resolution (FWHM) was ~36 keV. These values are lower than those warranted when supplied before 20 years. The minimum detectable activity (MDA) of the detectors varies between 0.8 and 3.1 mBq for the chamber in use. The alpha spectrometer was also verified by certified reference samples to measure activity concentration of alpha emitters (e.g., 238U, 232Th, 226Ra and 241Am) with acceptable coefficient of variance (<10%), ζ-score (<3) and P-test (<25%). As a result, the optimized alpha spectrometer is valid and can be utilized for monitoring and assessment of natural and artificial α-emitters in different environmental compartments.

234U, 238U, 226Ra, 228Ra and 40K concentrations in feed coal and its combustion products during technological processes in the Upper Silesian Industrial Region, Poland

Hard coal is the predominant energy source in Poland. The unavoidable consequence of coal combustion is the production of huge amounts of ash which can be concentrated in radionuclides. The ashes from coal combustion are utilized or stored and may affect the quality of the environment. Therefore, the estimation of radionuclides in hard coal and by-products is of crucial importance. The analyzed samples included ashes produced in ash furnaces, power plants and individual home furnaces operating in the Upper Silesian Industrial Region, Southern Poland, during the hard coal burning. This paper presents radioactivity concentrations of 228Ra, 226Ra and 40K in hard coal, bottom and fly ash samples from Polish coal-fired power plants obtained during various technological coal combustion processes and generated in individual domestic furnaces, determined using the HPGe gamma spectrometry technique. The measurements of 234,238U concentrations were performed after sample preparation using alpha-particle spectrometer. The concentrations of the obtained radionuclides differ greatly in the fly and bottom ash samples. The lowest concentrations of 226Ra, 228Ra, 234U, 238U were observed in bottom ashes from the co-firing of hard coal and biomass in a fluidized-bed furnace, whereas the highest concentrations of 226Ra (163 ± 6 Bq/kg), 228Ra (100 ± 2 Bq/kg) isotopes were found in the ashes from individual household furnaces. This means that both the feed coal type and combustion techniques have a direct impact on the concentration of radionuclides in ash. Hard coal silt samples may be enriched in radionuclides and the radioactive equilibrium between 226Ra and 238U even in the case of coal is not always achieved. The concentrations of the analyzed isotopes in ashes are 5-7-fold higher than in feed coal. Given that combustion by-products are utilized as construction products, it should be noted that for some ash samples, the radiological hazard indices approach or exceed the maximum permitted levels.

Alpha particle detection by Makrofol® DE1-1 and CR-39 NTDs: A comparative study

In this present study, a color contrast approach was proposed to find a method for quantify uncertainty in alpha particle spectroscopy using nuclear track detectors (NTDs). According to this method, this color contrast approach was applied to NTDs as an alpha particle spectrometer. A comparison between the registration of 4.0 MeV alpha particles by Makrofol®DE1-1 and CR-39 NTDs using a color contrast method was carried out in alpha spectroscopy. The contrast of the alpha tracks of each single color channel whether red, green and blue resulting from split RGB image was determined. The measurements were proved that green color channel produced the highest contrast of the alpha tracks of about 85%, in both Makrofol® DE1-1 and CR-39 NTDs. The results of 4.0 MeV alpha particle etch-pits diameters in Makrofol® DE1-1 didn't show homogenous diameters for short etching time. The standard deviation of 4.0 MeV alpha-track diameters in Makrofol® DE1-1 went up to a maximum value of 2.23 μm at a removal thickness of 12.25 μm. When increasing the etching time, they decreased sharply to about 1.18 ± 0.02 μm at a ratio of change 0.047 that was less than 6%. The standard deviation of 4.0 MeV alpha particle etch-pit diameters in CR-39 detector was linearly correlated with the removal thickness at a ratio of change of 0.02 which was less than 5%. Results revealed that the etch-pit diameter in Makrofol® DE1-1detector, in alpha particle spectrometry was best measured around the end of the alpha particle range. Results of this study are discussed within the frame work of nuclear track formation theories and etching mechanism in nuclear track detectors (NTDs).

Development of an alpha dust monitor using a GPS scintillator plate

A dust monitor with a silicon surface barrier detector (SSBD) is introduced at a nuclear fuel facility to detect airborne contamination of 238Pu and 239Pu released by past accidents. However, an SSBD frequently produces false alarms, especially in a room with high humidity. To develop a highly reliable dust monitor, we developed an alpha-particle spectrometer based on a cerium-doped Gd2Si2O7 (GPS) scintillator plate and a photomultiplier tube (PMT). The GPS scintillator plate is hexagonal and 50 mm in diameter, and the scintillator layer is approximately 40 μm. An output signal from the PMT is amplified by a preamp and transferred to an MCA. Then, an energy spectrum is displayed in real time. The 241Am alpha source, Rn progeny collected on the air filter, and a PuO2 particle were measured by our developed spectrometer. The energy resolution for 5.5-MeV alpha particles was ∼11.9% ± 0.2% of the FWHM. The efficiency was 92%, and it had a uniform sensitivity. By applying an energy window, the count-rate of the Rn progeny decreased by 77%. The GPS scintillator plate was able to measure the alpha spectrum even though the GPS scintillator got wet. Therefore, the alpha dust monitor using the GPS scintillator plate is ideal for detecting alpha-particle emitters in places lacking temperature and humidity controls, such as the outside of buildings.

SILICON DIODE AS AN ALPHA PARTICLE DETECTOR AND SPECTROMETER FOR DIRECT FIELD MEASUREMENTS.

A windowless silicon (Si) diode (4 mm(2)) was evaluated as alpha particle detector and spectrometer for field measurements. It was irradiated with alpha particles from a (241)Am (2.3 kBq) and a (210)Po (9 kBq) source at source-detector distances (SDD) of 0.5, 1.0 and 1.8 cm. The energy resolution in terms of full width at half maximum was 281, 148 and 113 keV for SDD of 0.5, 1.0 and 1.8 cm, respectively. The minimum detectable activity increased from 0.08 to 0.83 Bq when the SDD increased from 0.5 to 1.8 cm. The detector has the potential for several alpha spectrometric applications, such as monitoring for wound, skin and surface contamination at nuclear fuel facilities, nuclear power plants and facilities handling radioactive waste. Other areas are environmental surveys following releases of actinides at accidents in nuclear power plants and in connection with other radiological or nuclear scenarios.

High-resolution alpha-particle spectrometry based on 4H silicon carbide semiconductor detectors

Semiconductor detectors made of 4H-SiC material are desirable for applications in harsh environments with high temperature and/or intense radiation. We report the energy resolution and energy linearity of 4H-SiC semiconductor detector using as an alpha particle spectrometer. The leakage current of the 4H-SiC detector is only 14.92 nA/cm2, when a reverse bias of 200 V is applied on it. The energy resolution and energy linearity of 4H-SiC detector are studied using a 226Ra alpha source. The energy resolution of the 4H-SiC detector is 0.61%-0.90% for the 4.8-7.7 MeV alpha particles, which is comparable with the energy resolution results of commercial silicon detectors. The energy linearity of the 4H-SiC detector is very attractive, with the linearly dependent coefficient as good as 0.999 99. This work demonstrates the outstanding energy resolution and energy linearity properties of 4H-SiC semiconductor detectors.

基于4H-SiC的高能量分辨率α粒子探测器

Semiconductor detectors made of 4H-SiC material are desirable for applications in harsh environments with high temperature and/or intense radiation. We report the energy resolution and energy linearity of 4H-SiC semiconductor detector using as an alpha particle spectrometer. The leakage current of the 4H-SiC detector is only 14.92 nA/cm2, when a reverse bias of 200 V is applied on it. The energy resolution and energy linearity of 4H-SiC detector are studied using a 226Ra alpha source. The energy resolution of the 4H-SiC detector is 0.61%-0.90% for the 4.8-7.7 MeV alpha particles, which is comparable with the energy resolution results of commercial silicon detectors. The energy linearity of the 4H-SiC detector is very attractive, with the linearly dependent coefficient as good as 0.999 99. This work demonstrates the outstanding energy resolution and energy linearity properties of 4H-SiC semiconductor detectors.

Studying the physical parameters of a solid state nuclear track detector

Solid state nuclear track detectors (SSNTDs) are widely used to measure various types of ionizing radiation. Thus, studying the physical parameters of SSNTDs, such as the bulk etch rate, the track etching efficiency and detector sensitivity which could affect the registration efficiency, is important. This paper presents a simple technique used to study the dependence of those characteristic physical parameters of SSNTDs on the alpha-particle energy. The detector sensitivity and the alpha track diameter were found to decrease exponentially with increasing alpha-particle energy’s, which implies that the SSNTDs can be used as alpha-particle spectrometers. The bulk etch rates of the LR-115 and the CR-39 detectors were found to be 3.75 ± 0.21 µm h−1 and 1.72 ± 0.14 µm h−1, respectively. Moreover, the calibration coefficients of the LR-115 and the CR-39 detectors, placed in a diffusion cup with a fiberglass filter exposed to radon source inside a 50 L calibration chamber (supplied by Genitron, Germany), were found to be 0.036 ± 0.004 and 0.17 ± 0.03 [α-tracks cm−2 per (Bq m−3 day)], respectively.

A method to reproduce alpha-particle spectra measured with semiconductor detectors

A method is proposed to reproduce alpha-particle spectra measured with silicon detectors, combining analytical and computer simulation techniques. The procedure includes the use of the Monte Carlo method to simulate the tracks of alpha-particles within the source and in the detector entrance window. The alpha-particle spectrum is finally obtained by the convolution of this simulated distribution and the theoretical distributions representing the contributions of the alpha-particle spectrometer to the spectrum. Experimental spectra from (233)U and (241)Am sources were compared with the predictions given by the proposed procedure, showing good agreement. The proposed method can be an important aid for the analysis and deconvolution of complex alpha-particle spectra.

An SiC/GaN Detector/Front-End Detection System for High-Resolution Alpha-Particle Spectroscopy

An alpha-particle spectrometer has been assembled, consisting of an epitaxial 50 mum thick 4H silicon carbide (SiC) detector connected to a gallium-nitride (GaN) high-electron mobility transistor (HEMT) used as input transistor of the front-end electronics. The depleted layer of the SiC diode detector was sufficient to stop all alpha particles in the 4.8-MeV to 5.8-MeV energy range. An excellent energy resolution of ~ 0.9% has been obtained in this energy range at a temperature of 55degC. The energy-resolution limiting factor is found to be the dispersion of the energy loss in the gold Schottky contact, which acts as entrance window to the detector. We used a GaN front-end transistor because this material offers two important advantages over silicon: (1) it is a wide bandgap semiconductor and therefore is intrinsically more desirable for room and above-room temperature operation and (2) it can be grown on SiC substrates so as to realize SiC/GaN integrated systems. SiC-detector spectrometers are interesting in many nuclear applications where the operation environment is hostile, both in terms of ionising radiations and of high temperatures. Such applications include monitoring of ionising radiations in nuclear power plants and beam diagnostic in fundamental nuclear physics experiments.

Lunar Outgassing, Transient Phenomena, and the Return to the Moon. I. Existing Data

Herein the transient lunar phenomena (TLP) report database is subjected to a discriminating statistical filter robust against sites of spurious reports, and produces a restricted sample that may be largely reliable. This subset is highly correlated geographically with the catalog of outgassing events seen by the Apollo 15, 16 and Lunar Prospector alpha-particle spectrometers for episodic Rn-222 gas release. Both this robust TLP sample and even the larger, unfiltered sample are highly correlated with the boundary between mare and highlands, as are both deep and shallow moonquakes, as well as Po-210, a long-lived product of Rn-222 decay and a further tracer of outgassing. This offers another significant correlation relating TLPs and outgassing, and may tie some of this activity to sagging mare basalt plains (perhaps mascons). Additionally, low-level but likely significant TLP activity is connected to recent, major impact craters (while moonquakes are not), which may indicate the effects of cracks caused by the impacts, or perhaps avalanches, allowing release of gas. The majority of TLP (and Rn-222) activity, however, is confined to one site that produced much of the basalt in the Procellarum Terrane, and it seems plausible that this TLP activity may be tied to residual outgassing from the formerly largest volcanic ffusion sites from the deep lunar interior. With the coming in the next few years of robotic spacecraft followed by human exploration, the study of TLPs and outgassing is both promising and imperiled. We will have an unprecedented pportunity to study lunar outgassing, but will also deal with a greater burden of anthropogenic lunar gas than ever produced. There is a pressing need to study lunar atmosphere and its sources while still pristine. [Abstract abridged.]

Field validation of radon monitoring as a screening methodology for NAPL-contaminated sites

Abstract Screening methodologies aim at improving knowledge about subsurface contamination processes before expensive intrusive operations, i.e. drilling and core-sampling, well installation and development, sampling of groundwater and free-phase product, are implemented. Blind field tests carried out at a hydrocarbon storage and distribution center in NE Spain suggest that Rn monitoring can be effectively used to locate the boundaries of subsurface accumulations of NAPLs. Sixty seven measurements of Rn in soil air were performed with a SARAD RTM 2100 current-ionization alpha-particle spectrometer following a 10 m square grid. Reductions of 222Rn concentration above a pool of LNAPL due to the preferential partition of Rn into the organic phase were spatially analyzed and resolved to yield the surface contour of the NAPL source zone. This surface trace of the source zone agreed well with the extent and situation inferred from measurements of free-phase thickness taken at eight monitoring wells at the site. Moreover, the good repeatability (as measured by replicate measurements at the same sampling point) and spatial resolution of the technique suggest that the boundaries of the plume can be delineated at the sub-decametre level.

A very low-cost alpha-particle spectrometer

In this note a novel, very low-cost alpha-particle spectrometer has been described. The spectrometer's design is based on the concept of virtual instrumentation. It consists of a self-contained alpha probe connected to a PC through the USB bus and of PC application software. The probe uses a new arrangement of a large-area standard PIN photodiode and commercial off-the-shelf electronic components. The spectrometer has an energy resolution of 56 keV (239Pu) and a throughput of 103 cps. Due to its low-power consumption—not exceeding 200 mW—it can be used with laptop or palmtop computers as a portable spectrometer for field measurements.

α-Particle and γ-ray spectrometry of a plutonium solution for impurity determination

A highly enriched 240Pu solution was measured by α-particle and γ-ray spectrometry to determine other radionuclides present in the material as impurities. Low activities of 238Pu, 241Am, 243Cm and 244Cm were determined by measuring thin sources, made from the original solution, in a high-resolution alpha-particle spectrometer. The sources were prepared by evaporating the plutonium solution on quartz plates in a vacuum chamber. From the ingrowth of 241Am in the original solution, the amount of 241Pu could be calculated. After radiochemical separation of 241Am, the plutonium was measured by high-efficiency alpha-particle spectrometry to determine the amount of 238Pu. The enriched 240Pu material was also measured by high-resolution gamma-ray spectrometry, using two different HPGe detectors to determine the impurities of 239Pu and 241Am. The preparation of the sources and the measurement methods are described and discussed. The measured impurities, given in % of the 240Pu activity, are compared with the values on the certificate.

Recent outgassing from the lunar surface: The Lunar Prospector Alpha Particle Spectrometer

The Lunar Prospector Alpha Particle Spectrometer (APS) was designed to detect characteristic‐energy alpha particles from the decay of Rn‐222, Po‐218, and Po‐210 and to therefore map sites of radon release on the lunar surface. These three nuclides are radioactive daughters from the decay of U‐238; hence the background level of alpha particle activity is a function of the lunar crustal uranium distribution. Radon reaches the lunar surface either at areas of high soil porosity or where fissures release the trapped gases in which radon is entrained. Once released, the radon spreads out by “bouncing” across the surface on ballistic trajectories in a random‐walk process. The half‐life of Rn‐222 allows the gas to spread out by several hundred kilometers before it decays (depositing approximately half of the Po‐218 recoil nuclides on the lunar surface) and allows the APS to detect gas release events up to several days after they occur. The long residence time of the Pb‐210 precursor to Po‐210 allows the mapping of gas vents which have been active over the last approximately 60 years. The APS found only a faint indication of Po‐218 alpha particles. However, the Rn‐222 alpha particle map shows that radon gas was emanating from the vicinity of craters Aristarchus and Kepler at the time of Lunar Prospector. The Po‐210 alpha particle distribution reveals a variability in time and space of lunar gas release events. Po‐210 and Rn‐222 detections are associated with both thorium enhancements and lunar pyroclastic deposits.

Sequential isotopic determination of plutonium, thorium, americium, strontium and uranium in environmental and bioassay samples

A procedure has been developed to provide sequential analysis of 238Pu, 230Th, 241Am, 238U, and 90Sr in environmental and bioassay samples. Tracers and/or carriers ( 242Pu, 243Am, 232U, and stable strontium) are added into the sample as chemical yield monitors, and then, plutonium, thorium, strontium, americium, and uranium are sequentially separated and purified by Dowex ion-exchange resin, EiChroM Sr-resin, EiChroM TRU-resin, and Chelate-100 resin, respectively. The radioactivities of 90Sr and the actinides are measured using the liquid scintillation counter and alpha-particle spectrometer, respectively. Acidified water, glass-fiber air filter, soil, synthetic urine and synthetic feces samples of US National Institute of Standard and Technology Radiochemical Intercomparison Program(NRIP) were analyzed to verify this method. All the analytical results of 238Pu, 230Th, 90Sr, 241Am and 238U meet the traceability limit per ANSI N42.22, and when appropriate, evaluation of radiobioassay measurement bias and precision per ANSI N13.30.

Alpha-particle energy loss measurement of microgram depositions of biomolecules.

A commercially available alpha-particle spectrometer and 210Po alpha-particle source were used to determine the mass of microgram quantities of biomolecules. Samples were deposited in microliter volumes on thin silicon nitride windows and dried. The energy loss of the alpha-particles after traversing the sample was converted to a mass using tabulated alpha-particle stopping powers. The measurement was absolute, independent of biomolecule species, and no standards were needed for quantitation. The method has a dynamic range of 0.1-100 microg for deposits of diameter 1-2 mm. The precision varies from approximately 20% at 100 ng to a few percent at 5-100 microg. The silicon nitride windows allow multimodal analysis of the same quantified sample, including PIXE probing of elemental abundances, molecular identification by mass spectrometry, and isotopic quantitation of interactions. The method was used with accelerator mass spectrometry to quantify specific activities of microgram quantities of 14C-labeled proteins.

LUNAR PROSPECTOR: FIRST RESULTS AND LESSONS LEARNED

Lunar Prospector, the first competitively selected mission in NASA's Discovery Program, is conducting a one-year orbital survey of the Moon's composition and structure. Launched on January 6 1998, the suite of five instruments is measuring water/ice to a sensitivity of 50 ppm (hydrogen), detecting key elemental constituents, gas release events and mapping the Moon's gravitational and magnetic fields. The mission is described with emphasis on the first scientific results and lessons learned from managing a very low cost project. A mission overview and systems description is given along with final mission trajectories. Lessons learned from government–industry teaming, new modes of project management, and novel contractual arrangements are discussed. The suite of five instruments (neutron spectrometer, alpha particle spectrometer, gamma-ray spectrometer, electron reflectometer and magnetometer) is outlined with attention to final technical performance as well as development on a constrained budget and schedule. A review of our novel approaches to education and public outreach is discussed and a summary with suggestions and implications for future missions is provided.

Experimental validation of an analytical method to obtain the response function of an alpha particle spectrometer

In a previous paper, one of the authors suggested an analytical method for calculation of the response function of an alpha spectrometer for the case of large solid angles. This paper describes the experimental verification of the method. Spectra of a well-known natural uranium sample were measured with a 450 mm 2 Si detector and compared to the theoretical predictions. The measurements were carried out with two different geometrical configurations. In both cases a good agreement was observed between experimental and theoretical results.