Alpha Detector Research Articles

Chapter 15 Diffuse soil emanations of radon and hazard implications at Furnas Volcano, São Miguel Island (Azores)

Abstract Furnas Caldera Volcanic Complex, São Miguel Island (Azores), last erupted in 1630 and is famous for its intense hydrothermal activity (i.e. fumarolic fields, thermal springs, cold CO 2 -rich mineral waters and diffuse CO 2 soil emanations), which directly affect the villages of Furnas and Ribeira Quente. Here we report the first systematic investigations and mapping of soil radon ( 222 Rn) emanations in the Furnas Volcanic Complex, and we examine their potential health risks for local inhabitants. 222 Rn in volcanic soils (60 cm depth) was repeatedly measured between 2005 and 2010 using a portable solid-state alpha detector (RAD7, Durridge Company Inc.). Results reveal a local background of 8000 Bq m −3 and several areas with anomalously high 222 Rn activity (up to c. 400 000 Bq m −3 ), which coincide with advective or convective gas transport through volcanic structures and active fault zones. High 222 Rn radioactivity in Furnas and Ribeira Quente villages represents a risk to the population. Continuous monitoring performed during November and December 2005 in a house in Furnas shows indoor 222 Rn reaching 13 273 Bq m −3 , two orders of magnitude greater than the reference level (150 Bq m −3 ), when the ventilation efficiency is reduced.

Detection of fast neutrons from shielded nuclear materials using a semiconductor alpha detector

The response of a semiconductor alpha detector to fast (>1MeV) neutrons was investigated by using measurements and simulations. A polyethylene converter was placed in front of the detector to register recoil protons generated by elastic collisions between neutrons and hydrogen nuclei of the converter. The developed prototype equipment was tested with shielded radiation sources. The low background of the detector and insensitivity to high-energy gamma rays above 1MeV are advantages when the detection of neutron-emitting nuclear materials is of importance. In the case of a 252Cf neutron spectrum, the intrinsic efficiency of fast neutron detection was determined to be 2.5×10−4, whereas three-fold greater efficiency was obtained for a 241AmBe neutron spectrum.

Statistics of piezonuclear emissions: early results

Measurements of ionizing and nonionizing particles are performed during the rupture tests of steel rods having different diameter. A ZnS ( Ag ) alpha detector, a Geiger counter and a 3 He proportional counter for neutrons are used. From the distributions of the recorded intensity maxima, different particles emissions are suggested to occur in broken and nonbroken samples. A hint for the emission of neutrons at rupture is also obtained. Such neutron emissions are predicted in the framework of the piezonuclear theory.

ULTIMATE LEVELS OF EXPLOSIVES DETECTION VIA TAGGED NEUTRONS

Capabilities of the Tagged Neutron (TN) method for detection and identification of explosives materials (EM) are explored using an idealized geometrical model that includes a 14 MeV neutron generator with an integrated alpha detector, a gamma-ray detector based on BGO/LYSO crystals, and irradiated samples in the form of simulated EM (TNT, tetryl, RDX, etc.) or benign material (BM) such as cotton, paper, etc. Research was carried out under the framework of computational simulations of neutron physics processes by Monte Carlo methods as well as experimental measurements using an ING-27 neutron generator produced by VNIIA. The work resulted in a comparison between measured and simulated ROC (receiver operating characteristics) curves obtained via integration of analytically expressed functions of irradiation time, mass, and type of EM and BM. Experimental results indicate that 0.3 kg of tetryl simulant located 45 cm from the neutron generator is detected in 97% of cases after a one minute measurement, with the false-alarm rate being highly dependent on the type of BM present: from ∼0% in the case of water to ∼5% in the case of silk. Comparison of simulated and experimental data for these results shows they are in agreement in cases where the simulations account for neutron scattering from the object and background effects.

Alpha particle detector based on micropixel avalanche photodiodes

The main goal of this work is to study the possibility of detecting alpha particles with a micropixel avalanche photodiode (MAPD) in combination with Lutetium Fine Silicate (LFS) scintillators (500 μm thick). The results show that alpha detectors based on the MAPD are expected to be useful in many applications: public security (associated particle imaging for explosives and drugs detection), radioactive contamination monitoring in various environments, and detection of charged particles from nuclear reactions.

Radioactive source localization inside pipes using a long-range alpha detector

Long-range alpha detectors (LRADs) are attracting much attention in the decommissioning of nuclear facilities because of some problems in obtaining source positions on an interior surface during pipe decommissioning. By utilizing the characteristic that LRAD detects alphas by collecting air-driving ions, this article applies a method to localize the radioactive source by ions' fluid property. By obtaining the ion travel time and the airspeed distribution in the pipe, the source position can be determined. Thus this method overcomes the ion's lack of periodic characteristics. Experimental results indicate that this method can approximately localize the source inside the pipe. The calculation results are in good agreement with the experimental results.

Estimation of annual effective dose due to Radon level in indoor air and soil gas in Hamirpur district of Himachal Pradesh

Indoor air and soil gas radon measurements are simultaneously performed in Hamirpur district of Himachal Pradesh using RAD7, a solid state alpha detector. The study is performed for the estimation of radon level and annual effective dose for indoor air. Different locations are selected and it is found that the variation of radon concentration in indoor air and soil gas in Hamirpur region ranges from 35Bqm−3 to 956Bqm−3 and 35 to 2280Bqm−3 having mean values 189.43Bqm−3 and 462.56Bqm−3 respectively. From indoor air, the total annual effective dose is calculated and it varies from 0.88mSvy−1 to 24.09mSvy−1 with mean value of 4.77mSvy−1. In general, it is found that the annual effective dose limit was within the recommended reference level (3mSvy−1to 10mSvy−1) of the world organisations. A good correlation between radon concentration in air and soil gas is observed.

Measurement of 222RN concentration in drinking water in Sakarya, Turkey

In this paper, the first measurement of (222)Rn concentrations in drinking water from wells, springs and bottled waters in the city of Sakarya, Turkey was presented. The measurements were performed using RAD 7, a solid-state alpha detector, with RAD H2O (radon in water) accessory manufactured by Durridge Company, Inc. The measured activity concentrations ranged from 1.98 to 20.80 Bq l(-1) with an average value of 9.05 Bq l(-1) for well water, from 0.75 to 59.65 Bq l(-1) with an average value of 13.78 Bq l(-1) for spring water and from 0.75 to 22.8 Bq l(-1) with an average value of 5.41 Bq l(-1) for bottled water. Although these results indicated relatively high (222)Rn concentrations compared with that from other parts of the Turkey, they are still below the World Health Organization recommended level of 100 Bq l(-1) for radon. Using the measured activities of (222)Rn, the age-dependent associated committed effective doses due to the ingestion of (222)Rn as a consequence of direct consumption of drinking water were calculated. The committed effective doses from (222)Rn were estimated to range from 2.59 to 205.97 µSv y(-1), from 1.55 to 123.28 µSv y(-1) and from 1.31 to 104.48 µSv y(-1) for age groups 1-2, 8-12 and >17 y, respectively.

Eight-Channel TES Microcalorimeter System for Detector and Source Development

Nuclear forensics and environmental monitoring require rapid isotopic analysis of trace samples that contain multiple radioisotopes with closely spaced alpha particle energies. Conventional measurement of such a sample typically requires expensive and time-consuming radiochemical separations, measurement of multiple subsamples by silicon alpha spectrometry, and destructive analysis by mass spectrometry. The superior energy resolution of microcalorimeter detectors allows isotopic analysis with a single nonconsumptive alpha spectrometry measurement. In order to bring microcalorimeter alpha detector technology towards the goal of a practical analytical instrument, we have developed an eight-channel transition-edge sensor microcalorimeter system to enable rapid detector and source development. This system is now fully functional, and has enabled the identification of instabilities in our alpha detector response that resulted in degraded performance. A redesigned set of detectors has been fabricated and tested, and has shown significantly improved response. With the improved detectors, we have been able to consistently achieve energy resolution of less than 1 keV full width at half maximum at 5.3 MeV. We have prepared electroplated sources that contain 239-Pu and 240-Pu, demonstrated the ability to resolve their ~ 5.1 MeV alpha energy peaks with 0.74 keV FWHM resolution, and shown that the 240/239-Pu isotopic ratios obtained from our microcalorimeter spectra are in statistical agreement with mass spectrometry results.

Evaluation of freestanding GaN as an alpha and neutron detector

The wide bandgap (3.39)eV and large dislocation energy of the III–V semiconductor gallium nitride (GaN) make this a desirable material for charged particle spectroscopy in high temperature, high radiation environments. While other research groups have established that charged particle detectors can be fabricated from high quality, thin films of molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) grown GaN, this work demonstrates the feasibility of ionizing radiation detectors created from significantly thicker freestanding n-type GaN, grown via hydride vapor phase epitaxy (HVPE). Detectors were fabricated by depositing Ni/Au pads on n-type GaN, forming a Schottky barrier diode. Capacitance–voltage measurements on the detectors showed an intrinsic carrier concentration in the range of 10−16cm−3–10–15cm−3, and indicated an inhomogeneous distribution between diodes on the same wafer. The radiation sensitivity of the fabricated detectors was analyzed using alpha particles from an 241Am source. Charge collection efficiency (CCE) calculations from these experiments indicate an efficiency of 100 percent. The detectors were also successfully used to detect neutron induced charged particles using a Li2O foil in a neutron beam.

Radon-thoron monitoring in Tatun volcanic areas of northern Taiwan using LR-115 alpha track detector technique: Pre-calibration and installation

In the present study, experiments have been carried out to calibrate LR-115 alpha detector films in bare and cup-mode exposure for the measurement of radon and thoron concentrations in soil gas. Results showed non-uniformity in track formation on the films in bare-mode exposure. However, in cup-mode exposure the non-uniformity was reduced to a greater extent. The calibration factors obtained for radon in bare- and cup-mode exposures are 0.049 and 0.034 tr. cm−2 per Bq m−3 d, respectively. An attempt has been made to calibrate the radon-thoron discriminative cup with LR-115 films for simultaneous measurements of radon and thoron. This paper also presents the preliminary results of radonthoron monitoring in Tatun volcanic areas of northern Taiwan for the first time using radon-thoron discriminators with LR-115 films. The results show that the safe temperature to install the LR-115 films in volcanic areas is ≤ 65°C and thoron concentration in the study area is low.

$Q$ Spectroscopy With Superconducting Sensor Microcalorimeters

The total reaction energy (Q) of individual nuclear decays was measured using microcalorimeters with transition-edge-sensor (TES) thermometers. For alpha-decaying actinides (e.g., U-235, Pu-239, Np-237, Am-241), Q is in the 4-6 MeV range. Nearly all of this energy goes into the relatively light alpha particle, and approximately 100 keV is left over for the much heavier, recoiling daughter atom. Alpha-particle energy spectroscopy with TES-microcalorimeters has shown the ability to simultaneously resolve peaks that overlap in conventional alpha spectroscopy, with resolution now less than 1 keV full-width-at-half-maximum (FWHM) at 5.3 MeV. For total reaction energy spectroscopy, we use the same TES design as our alpha detectors, but embed a small radioactive sample (of about 1 Bq) directly inside an absorber designed to capture all the emitted particles (alpha, recoil nucleus, electrons, X-rays) with near 100% efficiency. We have measured Q-spectra of alpha-decaying isotopes with spectral resolution of 2-3 keV FWHM. For some actinide analytical problems, the Q -spectrum is simpler than the alpha-spectrum: fewer peaks, further apart, and easier to quantify. We will discuss sensor design, methods for embedding radionuclides, and spectral data.

Increased Light Extraction From Inorganic Scintillators With Laser-Etched Microstructures

A technique of laser-etching repeating micrometer-scale structures into the exit surface of a thin, YAP:Ce scintillator to increase light extraction has been performed. Different etching techniques were performed on a single, monolithic crystal using varying laser power to study how light extraction is influenced by these different treatments. For the best case, a 90.4% increase in light extraction was measured without optical coupling, which compares to photonic crystal techniques. This technique finds application in associated particle imaging (API) where no optical coupling can be used for the alpha detector's scintillator, inside the Deuterium-Tritium (D-T) neutron generator vacuum. The surface characteristics of each treatment are quantified, and changes in light collection relative to a normal, polished surface are presented. Measurement of the number of detected photons is given for the case where no optical coupling is used between the scintillator and photosensor. Additionally, implications of performance improvements in YAP:Ce based alpha transducers within D-T generators, due to the measured increases in light collection, are presented.

Assessments on energy and efficiency calibration of an alpha spectrometry system using standard sources

Studies and evaluations of the main parameters of a high resolution multi-chamber alpha spectrometer and its full calibration using standard sources of 241Am, 233U and 244Cm are presented for the validation of the complex method of characterization of an alpha spectrometer dedicated for alpha radioactive concentration measurements of various environmental samples. The resolution and efficiency were determined at all possible source-detector distances for all eight solid state ORTEC ULTRA-AS detectors. In addition, the solid angles associated to different measurement geometries and the repeatability of the results were assessed. A detailed inter-comparison of the results was performed drawing important conclusions regarding the quality of the alpha detector response to the alpha radiation of the standard sources used in measurements.

Differentiation between the effect of temperature and pressure on radon within the subsurface geological media

Long-term continuous in-situ radon field monitoring was carried out in the southern region of Israel, at the Amram Mountain research tunnel in Elat and in shallow boreholes in the Gevanim valley in Makhtesh Ramon. This work shows that long-term radon monitoring based on simultaneous alpha and gamma measurement enables to differentiate between the impact of ambient temperature and pressure on radon transportation within porous media both in sites isolated from outer meteorological influence as in the Amram tunnel and in sites open to the influence of environmental conditions as in the Gevanim boreholes array. It was found that if the monitoring site is a closed measuring space with undisturbed environmental conditions, the radon in the air space will reach equilibrium with the radon in the rock. Then the radon time series as measured by both gamma and alpha detectors exhibit the same temporal variations. The results in this case indicate that the diurnal, intra-seasonal and seasonal variations in the radon concentration are clearly associated with the ambient temperature gradient outside the rock air interface, 100 m above the tunnel. In shallow, open boreholes, no equilibrium between the radon within the porous media and the radon in the open borehole air is necessarily established and the results of radon monitoring are different. Gamma detectors that measure the changes in radon concentrations in the porous rock indicated a clear correlation between radon concentrations and the daily variations of external surface temperature, from about 1 m up to 85 m. Yet the alpha detectors that measure the changes in radon concentrations in very shallow borehole air (about 1 m) reveal a clear anti-correlation with atmospheric pressure waves at semi-daily, daily, and intra-seasonal time scales. At depths of several tens of meters, outer pressure waves induce anti-correlated radon variations lasting the same time, but destroy the ordered radon daily periodicity in the measuring air space, although almost not disturbing the daily radon variation within the surrounding porous media.

Measurement of radon and thoron progeny size distributions and dose assessments at the mineral treatment industry in Thailand

A new portable type cascade impactor has been developed to determine the activity size distribution of radon and thoron progeny in a natural environment more efficiently. The modified impactor consists of 4 stages with a back up filter stage for the collection of aerosol samples. The aerosol cut points in the impactor are set for 10, 2.5, 1 and 0.5 μm at a flow rate of 4 L min−1. Five CR-39 chips were used as alpha detectors for each stage. In order to separate α particles emitted from radon and thoron progeny, CR-39 detectors are covered with aluminum-vaporized Mylar films. The thickness of each film is adjusted to allow α particles emitted from radon and thoron progeny to reach the CR-39 detectors. The technique has been successfully tested in field studies, particularly inside a mineral treatment industry in Thailand to estimate doses in the working environment. The dose calculations by lung dose evaluation program showed that activity median aerodynamic diameters played a significant role in determining the particle size distributions of the attached radon and thoron progeny. The dose conversion factor determined from short term measurements due to exposure from the inhalation of thoron and its progeny was found to be 4 times higher than comparable values for radon and its progeny. The effective dose for workers exposed to radon is about 4–6 times higher than thoron.

High-resolution alpha spectrometry at ambient air pressure—Towards new applications

An approach for alpha spectrometry is introduced that allows measuring alpha spectra at ambient air pressure with energy resolution comparable to measurements in vacuum. The developed prototype equipment uses a semiconductor alpha detector and a honeycomb collimator. Contamination of 1Bq/cm2 at any smooth and flat surface can be detected in approximately 10s data acquisition time, but longer time is needed for radionuclide identification. A hand-held instrument for in-situ measurements can be manufactured opening a wide range of novel applications in alpha spectrometry.

Benchmarking the Geant4 full system simulation of an associated alpha-particle detector for use in a D–T neutron generator

The position-sensitive alpha-particle detector used to provide the starting time and initial direction of D–T neutrons in a fast-neutron imaging system was simulated with a Geant4-based Monte Carlo program. The whole detector system, which consists of a YAP:Ce scintillator, a fiber-optic faceplate, a light guide, and a position-sensitive photo-multiplier tube (PSPMT), was modeled, starting with incident D–T alphas. The scintillation photons, whose starting time follows the distribution of a scintillation decay curve, were produced and emitted uniformly into a solid angle of 4π along the track segments of the alpha and its secondaries. Through tracking all photons and taking into account the quantum efficiency of the photocathode, the number of photoelectrons and their time and position distributions were obtained. Using a four-corner data reconstruction formula, the flood images of the alpha detector with and without optical grease between the YAP scintillator and the fiber-optic faceplate were obtained, which show agreement with the experimental results. The reconstructed position uncertainties of incident alpha particles for both cases are 1.198mm and 0.998mm respectively across the sensitive area of the detector. Simulation results also show that comparing with other faceplates composed of 500μm, 300μm, and 100μm fibers, the 10-μm-fiber faceplate is the best choice to build the detector for better position performance. In addition, the study of the background originating inside the D–T generator suggests that for 500-μm-thick YAP:Ce coated with 1-μm-thick aluminum, and very good signal-to-noise ratio can be expected through application of a simple threshold.

The use of solid angle for alpha detector efficiency in 226Ra analyses of soil samples

In the frame of proficiency tests organized by IAEA and IRMM, the specific activity concentration of radium-226 in soil has been measured. The BaSO4 co-precipitation technique has been used. Normally, in this method, the detector efficiency of the alpha spectrometer is determined using a 226Ra source with known activity. As an alternative to using a 226Ra standard, we calculated the detector efficiency from the relative solid angle subtended by the detector on the soil samples. The accuracy of this method depends on the uncertainty of geometrical properties and the distribution of activity within the source. An uncertainty budget is provided. The method was applied successfully in the intercomparisons.

A Study on Natural Radioactivity in Khewra Salt Mines, Pakistan

The Khewra Salt Mines, the second largest salt mines in the world, are located 160 km south of Islamabad, the capital of Pakistan. Around 1000 workers are involved in the removal of salt from these mines. More than 40,000 visitors come annually to see the mines. The visitors and workers are directly exposed to the internal and external radiological hazards of radon and gamma rays in these mines. The general public is affected by the intake of the salt containing the naturally occurring radionuclides. Therefore the concentration of radon (²²²Rn) in the Khewra Salt Mines and activity concentrations of the naturally occurring radionuclides in the salt samples from these mines were measured. Both active and passive techniques were employed for the measurement of radon with Radon Alpha Detector (RAD-7) and SSNTD respectively. The concentration of ²²²Rn was 26 ± 4 Bq m⁻³ measured by the active method while 43 ± 8 Bq m⁻³ was measured by the passive method. The activity concentration of the radionuclides was measured using gamma ray spectrometry with HPGe detector. The mean activity of ⁴⁰K in salt samples was found to be 36 ± 20 Bq kg⁻¹ and the concentration of ²²⁶Ra and ²³²Th in the salt samples was below the detection limits. Gamma radiation hazard was assessed in terms of the external gamma dose from salt slabs and the rooms made of salt and the annual effective dose due to gamma radiation. The exposure to radon daughters, annual effective dose and excessive lifetime cancer risk due to radon in the mines were estimated. The mean annual effective dose due to an intake of ⁴⁰K from the salt was calculated as 20.0 ± 11.1 µSv, which is lower than the average annual effective dose rate of 0.29 mSv, received by the ingestion of natural radionuclides. Due to the low concentration values of primordial radionuclides in the salt and radon ²²²Rn) in the mines, a 'low level activity measurement laboratory' is suggested to be established in these mines.