Detection Of Α-particles Research Articles

Enhancing the radiation hardness of vertical 4H–SiC detectors by the metal-oxide-semiconductor structure

In this work, 4H–SiC α-particle detectors with metal/semiconductor (MS) and metal/oxide/semiconductor (MOS) structures have been fabricated. The effects of introducing a SiO2 dielectric layer to form a MOS structure on the electrical properties, the performances, and the radiation hardness of the detectors have been evaluated systematically by comparing those with the MS structure. It is found that the reverse leakage current and the signal-to-noise ratio of α-particle detectors at high voltages can be improved by the MOS structure. Furthermore, the MOS structure exhibits much higher radiation hardness, as the energy resolution degradation of α particle detectors with MOS and MS structures after the γ irradiation is 0.59% and 2.87%, respectively. This work may provide a way to enhance the radiation hardness of 4H–SiC α-particle detectors.

A methodology for alpha particles identification in liquid scintillation using a cost-efficient Artificial Neural Network

The discrimination of α/β-particles based on Liquid Scintillation (LS) is a measurement technique that can be applied for environmental monitoring. This technique relies on the specific feature of the scintillation process yielding two decay components (fast and delayed) of the photon emission following a particle interaction in a LS sample; indeed, the intensity of the delayed component is higher for α-particles than for β-particles. When operating with a photon detector such as a PhotoMultiplier Tube (PMT), the Pulse-Shape Discrimination (PSD) is the traditional approach, relying on low-pass filtered signals allowing pulse-tail analysis for an α-particle identification. This paper presents a new α-particle detection method based on an Artificial Neural Network (ANN) that directly processes fast pulse trains produced by the delayed scintillation component of a single detector. The ANN is trained using an experimental dataset obtained with a single PMT channel connected in a 3-PMTs detection system from which triple coincidences resulting from α-interactions (241Am) in a LS source are used for the single detector labeling. As we target a real-time implementation, the ANN is designed to minimize the computational resources. The classifier can operate with good performances (91.0% of correct classification, 8.5% false negative and 0.5% false positive) on a single-channel detector.

Development of local-power-free, remote α-particle detection using optical fibers.

We demonstrate the application of fluorescence optical fiber coupled to a telecom grade fiber as a sensor for alpha particles using alpha-specific ZnS(Ag) scintillation materials whose wavelength is down-shifted into a low-loss region of the telecom grade fiber transmission band. Telecom-grade fiber optics offer a solution for sensing alpha radiation in deep repositories and cask storage for radioactive materials due to the stability of SiO2 under normal environmental conditions and its relative radiation hardness at low radiation doses. Long-term nuclear waste storage facilities require sensors for the detection of leakage of radioactive materials that are maintenance-free, do not require power and can survive with no 'wear out' mechanisms for decades. By accomplishing the wavelength transformation, we maximize efficiencies in the detection of α-particles and signal transport and can detect alpha scintillation at distances on the order of >1km with a sensor that is ~3% efficient and can be easily scaled as a sensor array. This paper describes the construction and testing of the sensor including manufacture of the controlled thickness films, verification of the wavelength shift from 450to 620nm and optimization of the sensitivity as a function of thickness. We also model the relative sensitivity of the film as a function of film thickness, and we demonstrate a signal-to-noise ratio of 10 at a range of greater than 1km.

α(PS)–γ(Ge) digital anti-coincidence spectroscopy and its application to activity measurement of 225Ac

Activity of 225Ac was measured by the digital anti-coincidence spectroscopy technique using a 4πα–γ detector configuration, composed of a sandwich type 4π plastic scintillator and Ge detectors. Ultrathin plastic scintillators were used for selective detection of α-particles emitted from 225Ac and its progenies, and the α-counting efficiencies of a 4π plastic scintillation detector for individual nuclides in the decay chain were determined as well. A list-mode multichannel analyzer was employed to record coincidence/anti-coincidence events for off-line analyses. The time difference distribution spectra revealed α-particle emission following 213Po decay without β-particle interference from 213Bi.

Study of the Sensitivity Limit of Detection of α-Particles by Polymer Film Detectors LR-115 Type 2 Using X-ray Diffraction and UV-Vis Spectroscopic Methods.

This work is devoted to the applicability assessment of optical spectroscopy and X-ray diffraction methods to establish the lower detection limit for the density of latent tracks from α-particles in polymer nuclear-track detectors, in the case of simulation of the formation of radon decay daughter products using Am-241 sources. During the studies, the detection limit for the density of latent tracks-traces of the interaction of α-particles with the molecular structure of film detectors-was established using optical UV spectroscopy (104 track/cm2) and X-ray diffraction (104 track/cm2). At the same time, analysis of the connection between structural and optical changes in polymer films indicates that a growth in the density of latent tracks above 106-107 results into the formation of an anisotropic change in the electron density associated with distortions in the molecular structure of the polymer. An analysis of the parameters of diffraction reflections (the position and width of the diffraction maximum) showed that in the range of latent track densities of 104-108 track/cm2, the main changes in these values are associated with deformation distortions and stresses caused by ionization processes during the interaction of incident particles with the molecular structure of the polymer. The increase in optical density, in turn, is caused by the accumulation of structurally changed regions (latent tracks) in the polymer as the irradiation density increases. A general analysis of the obtained data showed good agreement between the optical and structural characteristics of the films depending on the irradiation density.

Sub-Nanosecond 2D Perovskite Scintillators by Dielectric Engineering.

Perovskite materials have demonstrated great potential for ultrafast scintillators with high light yield. However, the decay time of perovskite still cannot be further minimized into sub-nanosecond region, while sub-nanosecond scintillators are highly demanded in various radiation detection, including high speed X-ray imaging, time-of-flight based tomography or particle discrimination, and timing resolution measurement in synchrotron radiation facilities, etc. Here, a rational design strategy is showed to shorten the scintillation decay time, by maximizing the dielectric difference between organic amines and Pb-Br octahedral emitters in 2D organic-inorganic hybrid perovskites (OIHP). Benzimidazole (BM) with low dielectric constant inserted between [PbBr6 ]2- layers, resulting in a surprisingly large exciton binding energy (360.3 ± 4.8 meV) of 2D OIHP BM2 PbBr4 . The emitting decay time is shortened as 0.97ns, which is smallest among all the perovskite materials. Moreover, the light yield is 3190photonsMeV-1 , which is greatly higher than conventional ultrafast scintillator BaF2 (1500photonsMeV-1 ). The rare combination of ultrafast decay time and considerable light yield renders BM2 PbBr4 excellent performance in γ-ray, neutron, α-particle detection, and the best theoretical coincidence time resolution of 65.1ps, which is only half of the reference sample LYSO (141.3ps).

Chemically vapor deposited oxide-based thick film scintillators

Radiation detection and imaging are used for nondestructive testing in the field of production technology, diagnosis and treatment in the medical field, and security activities at airports and nuclear facilities. To improve sensitivity and resolution in radiation detection and imaging, light scattering and self-absorption in scintillator media should be suppressed. Thick film scintillators with a thickness of several tens of micrometers have recently attracted attention; however, mechanical thinning of single crystal bulk or sintered polycrystalline transparent ceramics is costly. In this review, we discuss advantages of thick film scintillators for α-particle detection and X-ray imaging with numerical simulations and introduce a novel process that enables direct and rapid synthesis of thick film scintillators of tungsten- and lutetium-based practical oxide materials using a chemical vapor deposition method.

The physical mechanism of alpha-particle-air interaction and analysis of long-range secondary particles yield

The α-particle detection has a pivotal role in radiation measurement. Standoff α-particle detection has advantages such as high efficiency and safety compared with the traditional method. However, the low yield of the characteristic signal significantly limits the broad application of this technique. To efficiently perform standoff detection of α-particle, the physical mechanism of α-particle interaction with air, the various secondary effects generated, and the yields are systematically analyzed in this paper. The results show that in addition to the radioluminescence, which is the focus of most current studies, the characteristic X-rays also meet the requirements as a characteristic signal for standoff detection. The processes of induced generation of these two secondary particles in the air are studied, the yields of characteristic X-rays of nitrogen and oxygen atoms and the yields of radioluminescence photons in the near-ultraviolet (UVA/UVB) and deep-ultraviolet (UVC) bands are given, respectively. The interference brought by the presence of β-particles and γ-particles to the α-detection when the radiation field is more complex is also quantitatively analyzed.

Development of 222Rn Emanation Sources with Integrated Quasi 2π Active Monitoring.

In this work, a novel approach for the standardization of low-level 222Rn emanation is presented. The technique is based on the integration of a 222Rn source, directly, with an α-particle detector, which allows the residual 222Rn to be continuously monitored. Preparation of the device entails thermal physical vapor deposition of 226RaCl2 directly onto the surface of a commercially available ion implanted Si-diode detector, resulting in a thin-layer geometry. This enables continuous collection of well resolved α-particle spectra of the nuclei, decaying within the deposited layer, with a detection efficiency of approximately 0.5 in a quasi 2π geometry. The continuously sampled α-particle spectra are used to derive the emanation by statistical inversion. It is possible to achieve this with high temporal resolution due to the small background and the high counting efficiency of the presented technique. The emanation derived in this way exhibits a dependence on the relative humidity of up to 15% in the range from 20% rH to 90% rH. Traceability to the SI is provided by employing defined solid-angle α-particle spectrometry to characterize the counting efficiency of the modified detectors. The presented technique is demonstrated to apply to a range covering the release of at least 1 to 210 222Rn atoms per second, and it results in SI-traceable emanation values with a combined standard uncertainty not exceeding 2%. This provides a pathway for the realization of reference atmospheres covering typical environmental 222Rn levels and thus drastically improves the realization and the dissemination of the derived unit of the activity concentration concerning 222Rn in air.

Application and Development of Noncontact Detection Method of α-Particles Based on Radioluminescence

The detection of α particles is of great significance in military and civil nuclear facility management. At present, the contact method is mainly used to detect α particles, but its shortcomings limit the broad application of this method. In recent years, preliminary research on noncontact α-particle detection methods has been carried out. In this paper, the theory of noncontact α-particles detection methods is introduced and studied. We also review the direct detection and imaging methods of α particles based on the different wavelengths of fluorescence photons, and analyze the application and development of this method, providing an important reference for researchers to carry out related work.

A new all-inorganic vacancy-ordered double perovskite Cs2CrI6 for high-performance photovoltaic cells and alpha-particle detection in space environment

Although MAPbI3 photovoltaics have gained increasing interest for space application, its low stability and radiation resistance is insurmountable. Here, we unexpectedly find a new vacancy-ordered double perovskite Cs2CrI6 to realize high-performance space solar cells and α-particle detectors through an innovative multi-scale simulation strategy based on the first-principle calculations coupling with drift-diffusion model and Monte Carlo method. Compared to the MAPbI3, Cs2CrI6 possesses more excellent stability and optical absorption, suitable band gap (1.08 eV), higher mobility (∼103 cm2/V) and lower capture cross-section. These lead to the ultra-high power conversion efficiency (PCE) for single-junction solar cells (22.4%) and monolithic all-perovskite tandem solar cells (26.6%), and excellent α-particle detectors with ultra-high charge collection efficiency (CCE = 99.3%) and mobility-lifetime product (μτh = 4.99 × 10−3 cm2V−1), which are superior to those of corresponding MAPbI3 devices. Meanwhile, the 90% of initial PCE can be remained even under the 5 × 1013 p. cm−2 fluence proton beam and several orders higher than traditional space solar cell. Moreover, the proton irradiation resistance of Cs2CrI6 α-particle detection can reach up to 1016 p. cm−2. The excellent device performance and irradiation resistance of Cs2CrI6 devices indicate the great potential application in photovoltaic cells, α-particle detectors and even their space applications.

Vertical GaN-on-GaN Schottky Diodes as α-Particle Radiation Sensors.

Among the different semiconductors, GaN provides advantages over Si, SiC and GaAs in radiation hardness, resulting in researchers exploring the development of GaN-based radiation sensors to be used in particle physics, astronomic and nuclear science applications. Several reports have demonstrated the usefulness of GaN as an α-particle detector. Work in developing GaN-based radiation sensors are still evolving and GaN sensors have successfully detected α-particles, neutrons, ultraviolet rays, x-rays, electrons and γ-rays. This review elaborates on the design of a good radiation detector along with the state-of-the-art α-particle detectors using GaN. Successful improvement in the growth of GaN drift layers (DL) with 2 order of magnitude lower in charge carrier density (CCD) (7.6 × 1014/cm3) on low threading dislocation density (3.1 × 106/cm2) hydride vapor phase epitaxy (HVPE) grown free-standing GaN substrate, which helped ~3 orders of magnitude lower reverse leakage current (IR) with 3-times increase of reverse breakdown voltages. The highest reverse breakdown voltage of −2400 V was also realized from Schottky barrier diodes (SBDs) on a free-standing GaN substrate with 30 μm DL. The formation of thick depletion width (DW) with low CCD resulted in improving high-energy (5.48 MeV) α-particle detection with the charge collection efficiency (CCE) of 62% even at lower bias voltages (−20 V). The detectors also detected 5.48 MeV α-particle with CCE of 100% from SBDs with 30-μm DL at −750 V.

Charge transport mechanism of self-powered GaN p-i-n α-particle detector

Abstract In this paper, a model based on charge collection efficiency (CCE) has been developed to investigate the charge transport mechanism of self-powered GaN p-i-n α-particle detector. To validate the model, a GaN p-i-n α-particle detector with 20 μm unintentionally doped layer was fabricated and irradiated by 5.48 MeV α particles. The contribution of hole diffusion to CCE was observed to be 17% at zero bias and slightly decreased to 14% at a reverse voltage of 10 V. The consistency between the experimental result and theoretical calculation demonstrates that charge transport mechanism is dominated by hole diffusion of non-depleted region. This work proves the appreciable advantage of GaN p-i-n detectors to detect α particles even without external power supply.

Study of tagged neutron method with laboratory D-T neutron generator for explosive detection

Tagged neutron-based experimental system has been developed with a laboratory D-T neutron generator at BARC. The system can identify the C, N, O elemental signatures from an interrogated object (explosive or benign) using the Associated Particle Technique (also known as tagged neutron method) employing alpha–gamma coincidence and time-of-flight methodology. The system consists of a matrix of 64-pixel YAP:Ce α-particle detectors incorporated in the neutron generator and a BGO (3″ × 3″) gamma detector. Main parameters of the system were investigated, and its performance was evaluated through various experiments performed at laboratory environment. The experimental results of pure element spectra (graphite for Carbon, water for Oxygen), complex sample (melamine) spectrum and study of explosive simulant (RDX) spectrum have demonstrated the successful implementation of the tagged neutron method.

Low Voltage High-Energy α-Particle Detectors by GaN-on-GaN Schottky Diodes with Record-High Charge Collection Efficiency.

A low voltage (−20 V) operating high-energy (5.48 MeV) α-particle detector with a high charge collection efficiency (CCE) of approximately 65% was observed from the compensated (7.7 × 1014 /cm3) metalorganic vapor phase epitaxy (MOVPE) grown 15 µm thick drift layer gallium nitride (GaN) Schottky diodes on free-standing n+-GaN substrate. The observed CCE was 30% higher than the bulk GaN (400 µm)-based Schottky barrier diodes (SBD) at −20 V. This is the first report of α–particle detection at 5.48 MeV with a high CCE at −20 V operation. In addition, the detectors also exhibited a three-times smaller variation in CCE (0.12 %/V) with a change in bias conditions from −120 V to −20 V. The dramatic reduction in CCE variation with voltage and improved CCE was a result of the reduced charge carrier density (CCD) due to the compensation by Mg in the grown drift layer (DL), which resulted in the increased depletion width (DW) of the fabricated GaN SBDs. The SBDs also reached a CCE of approximately 96.7% at −300 V.

Charge collection efficiency of Pt vs. Mg contacts on semi-insulating GaAs

A comparative study of diode structures based on semi-insulating (SI) GaAs with evaporated Mg vs. Pt contacts is presented. Electric field strength in the vicinity of the contacts is inferred from the detection of α-particles emitted from 241Am radioisotope. It is shown that at zero bias, the structure with Mg-based contacts (MgO/SI GaAs) gives comparatively small signal implying an ohmic behaviour. Contrary, the structure with Pt contacts reveals presence of a non-negligible electric field near the contacts at zero bias voltage, thus indicating presence of a sizeable space charge region near the interface. The results are supplemented by insights from atomistic electronic structure modeling of idealized GaAs/Pt vs. GaAs/Mg and GaAs/MgO interfaces.

Rapid detection of heavy elements in blood extracted from wounds using x-ray fluorescence analysis

In radiation emergency situations involving persons having plutonium (Pu)-contaminated wounds, rapid assessment of the degree of Pu contamination is required to determine the appropriate course of treatment. Currently, rapid on-site detection of Pu is usually performed by analysis of α-particles emitted from the adhesive tape peeled off the wound. However, the detection of α-particles is difficult, especially in traumatic skin lesions with oozing blood, because of the low permeability of α-particles in blood. Therefore, we focused on x-ray fluorescence (XRF) analysis because x-rays easily pass through several millimetres of blood. In this study, we developed a new methodology for the rapid detection of heavy elements in wounds based on XRF analysis of the contaminated blood collected by gauze patch and filter paper, using stable lead (Pb) as a model contaminant substitute for Pu. Mouse blood samples contaminated with Pb were dropped on gauze patches or absorbed by filter papers and were subjected to XRF measurement. Small pieces of filter paper served as more suitable extraction materials than gauze patches because the entire amount of blood absorbed could be measured. When we used filter paper, the signal intensity of the Pb Lα peak was proportional to the Pb concentration in the blood. With a measurement time of 30 s, the minimum detection limit of Pb in blood collected by filter paper was 2.4 ppm.

Method for measurement of radon diffusion and solubility in solid materials

Abstract Summary In order to study the permeation i.e. the diffusion and solubility of radon gas in biological material, a new setup was constructed and a novel analysis was applied to obtain diffusion and solubility coefficients. Thin slabs of solid materials were installed between detector housing and the surrounding radon exposure chamber of 50 Ls volume. In this setup radon can diffuse through thin test samples into a cylindrical volume of 5 mm height and 20 mm diameter and reach an α-particle detector. There the 5.49 MeV α-decay of the penetrating radon atoms is measured by a silicon surface barrier detector. The time dependent activities inside the small detector volume are recorded after injection of a known radon activity concentration into the outer chamber. Analyzing the time behavior of the integral α-activity from radon in the small vessel, both, the diffusion coefficient and solubility of the test material can be determined, based on a new mathematical model of the diffusion process concerning the special boundary conditions given by the experimental setup. These first measurements were intended as proof of concept for the detection system and the data analysis. Thin polyethylene foils (LDPE) were selected as material for the diffusion measurements and the results were in agreement with data from literature. In further measurements, we will concentrate on biological material like bone, fat and other tissues.

Controlling alpha tracks registration in Makrofol DE 1-1 detector

Makrofol DE 1-1 is a recent type of solid state nuclear track detectors could be used to measure radon concentration in the environment throughout the detection of α-particles emitted from radon decay. Thus, studying the physical parameters that control the formation of alpha tracks is vital for environmental radiation protection. Makrofol DE 1-1 polycarbonate detector was irradiated by α-particles of energies varied from 2 to 5MeV emitted from the 241Am source of α-particle energy of 5.5MeV. Then, the detector was etched in an optimum etching solution of mixed ethyl alcohol in KOH aqueous solution of (85% (Vol.) of 6M KOH+15% (Vol.) C2H5OH) at 50°C for 3h. Afterward, the bulk etch rate, etching sensitivity, and the registration efficiency of the detector, which control the tracks registration, were measured. The bulk etch rate of Makrofol detector was found to be 3.71±0.71μmh−1. The etching sensitivity and the detector registration efficiency were decreased exponentially with α-particles’ energies following Bragg curve. A precise registration of α-particle was presented in this study. Therefore, Makrofol DE 1-1 can be applied as a radiation dosimeter as well as radon and thoron monitors.

Depth profiling Li in electrode materials of lithium ion battery by 7Li(p,γ)8Be and 7Li(p,α)4He nuclear reactions

A proton induced γ-ray emission method based on 7Li(p,γ)8Be proton capture reaction and a nuclear reaction analysis method involving 7Li(p,α)4He reaction are described for depth profiling Li in the electrode materials, graphite and lithium cobalt oxide for example, of a Li-ion battery. Depth profiling by 7Li(p,γ)8Be reaction is accomplished by the resonance at 441keV and involves the measurement of 14.6 and 17.6MeV γ-rays, characteristic of the reaction, by a NaI(Tl) detector. The method has a detection sensitivity of ∼0.2at% and enables profiling up to a depth ≥20µm with a resolution of ≥150nm. The profiling to a fairly large depth is facilitated by the absence of any other resonance up to 1800keV proton energy. The reaction has substantial off-resonance cross-sections. A procedure is outlined for evaluating the off-resonance yields. Interferences from fluorine and aluminium are major limitation of this depth profiling methodology. The depth profile measurement by 7Li(p,α)4He reaction, on the other hand, utilises 2–3MeV protons and entails the detection of α-particles at 90° or 150° angles. The reaction exhibits inverse kinematics at 150°. This method, too, suffers interference from fluorine due to the simultaneous occurrence of 19F(p,α)16O reaction. Kinematical considerations show that the interference is minimal at 90° and thus is the recommended angle of detection. The method is endowed with a detection sensitivity of ∼0.1at%, a depth resolution of ∼100nm and a probing depth of about 30µm in the absence and 5–8µm in the presence of fluorine in the material. Both methods yielded comparable depth profiles of Li in the cathode (lithium cobalt oxide) and the anode (graphite) of a Li-ion battery.