Energy Spectra Of Alpha Particles Research Articles

Demonstrating the β-Ga2O3 Schottky diodes for alpha radiation detection

Schottky barrier diodes were fabricated on (001) monoclinic β-Ga2O3 wafers with low doped epitaxial layers of 7.0 × 1015 cm−3. Circular Ni Schottky contacts with area 2 mm2 were deposited by electron beam evaporation. Devices were characterized electrically by performing forward and reverse current-voltage sweeps with a range of −100 V–2 V, as well as capacitance-voltage sweeps to −30 V. The breakdown voltage was also determined to be −180 V for the devices. Experiments measuring the electrical response from incident X-ray radiation was performed. A response time to X-ray radiation of less than 1 s was recorded and a decay time of approximately 2 s after removing X-ray source, which primarily attribute to X-ray switching on and off time. Energy spectra of alpha particles from a 0.9 μCi 241Am button source was collected at various voltage biases using devices with the lowest measured leakage current while reverse biased. The total count rate was observed to increase linearly with increasing device bias. The peak channel number was observed to increase with increasing bias with the best resolution of 9.5% at −100 V reverse bias.

High count rate alpha particle spectroscopy by a digital optical camera: A comparison study on edge detection algorithms

Alpha particle spectroscopy is highly significant in technologies related to radioactivity, particularly in radiation safety and the study of natural radioactivity. On the other hand, tools capable of identifying and determining the energies of alpha particles are of great interest. Among these tools, Commercial Off-The-Shelf (COTS) instruments, which can be used for alpha particle detection, have gained significant importance due to their ease of use and low cost. In this study, alpha particle spectroscopy of a Ra-226 source has been performed using a commercial digital camera based-on a CMOS sensor. In order to determine energy spectrum of alpha particles emitted from the source, the performance of various edge detection algorithms was examined. An algorithm based-on local pixel changes was introduced and implemented. By comparing the run times of the algorithms, it was shown that the algorithm proposed in this article exhibited the shortest run-time. Additionally, a method for rejecting pile-up events to correct their destructive effects on the alpha particle energy spectrum was introduced and implemented.

Source efficiency of alpha-emitters applied to the skin surface.

Skin surface contamination by alpha-emitters is in itself not hazardous, but it would cause significant internal exposure in the case of injured skin as well as misjudgment in direct in vivo measurements (e.g. lung counting). The present study determined the source efficiency of alpha-emitters (241Am) applied to swine skin samples by analysing the observed alpha-particle energy spectra using advanced alpha-spectrometric simulation. Based on our results, the source efficiency was determined to be 0.365 (alpha-particle s-1 per Bq) on average (c.f. 0.5 in the case of no self-absorption in the source). The decrease in source efficiency would be attributed primarily to the radionuclide entering hair follicles or deep wrinkles. The degradation of the measured spectra from the skin samples indicates the penetration of some radionuclides into the upper layers of the stratum corneum. Although this study was limited to results obtained from swine skin samples, it suggests that irregularities in the skin surface may affect direct alpha measurements.

Macroscopic and microscopic investigation of maximum effectiveness of proton-boron capture therapy using Monte Carlo simulation

Proton-boron capture therapy (PBCT) has been proposed as a new method to enhance effectiveness of proton therapy. There is, however, no consensus on its potential effectiveness. Most theoretical studies have been done at a macroscopic level. At cellular dimensions, however, the dose ratio with PBCT can be strongly favourable due to proton-boron reactions. The goal of this study was to investigate the theoretical maximum dose enhancement with PBCT, and its radiation physics mechanisms, through both macroscopic and microscopic simulations. The Monte Carlo simulations involved two stages due to model limitations. In the macroscopic calculations, variations in Bragg-peak height and depth caused by a 10 mm thick boron region were examined for different proton energies (62, 80 and 100 MeV) using MCNPX. Percentage depth doses and energy spectra of protons, alpha particles, neutrons and photons were also computed. The second stage used Geant4 for dose calculation in cellular dimensions. Macroscopically, the energy deposition peak shifted towards the surface by about 3.1 mm and the Bragg peak dose increased by up to 53.1%, 53.4%, 53.9% for proton energies 62, 80 and 100 MeV, respectively, compared to the proton-only (no boron) case. Microscopically, the calculated total equivalent doses for these energies showed 5%, 23% and 50% enhancements, respectively. The results suggest increased effectiveness with PBCT due to production of short-range alpha-particles, especially at higher incident proton energies. Also, by adding boron, the mean proton energy is reduced thereby increasing the probability of local dose deposition. The theoretical maximum possible improvement in dose equivalent in the target region at the cellular scale was shown to slightly increase with beam energy, reaching about 54% at the highest studied energy. This combined approach has provided further insight into the potential of PBCT. Further studies, particularly at higher proton energies, are indicated.

Development of a stand-alone precalculated Monte Carlo code to calculate the dose by alpha and beta emitters from the Ra-224 decay chain.

Recent developments in alpha and beta emitting radionuclide therapy highlight the importance of developing efficient methods for patient-specific dosimetry. Traditional tabulated methods such as Medical Internal Radiation Dose (MIRD) estimate the dose at the organ level while more recent numerical methods based on Monte Carlo (MC) simulations are able to calculate dose at the voxel level. A precalculated MC (PMC) approach was developed in this work as an alternative to time-consuming fully simulated MC. Once the spatial distribution of alpha and beta emitters is determined using imaging and/or numerical methods, the PMC code can be used to achieve an accurate voxelized 3D distribution of the deposited energy without relying on full MC calculations. To implement the PMC method to calculate energy deposited by alpha and beta particles emitted from the Ra-224 decay chain. The GEANT4 (version 10.7) MC toolkit was used to generate databases of precalculated tracks to be integrated in the PMC code as well as to benchmark its output. In this regard, energy spectra of alpha and beta particles emitted by the Ra-224 decay chain were generated using GAMOS (version 6.2.0) and imported into GEANT4 macro files. Either alpha or beta emitting sources were defined at the center of a homogeneous phantom filled with various materials such as soft tissue, bone, and lung where particles were emitted either mono-directionally (for database generation) or isotropically (for benchmarking). Two heterogeneous phantoms were used to demonstrate PMC code compatibility with boundary crossing events. Each precalculated database was generated step-by-step by storing particle track information from GEANT4 simulations followed by its integration in a PMC code developed in MATLAB. For a user-defined number of histories, one of the tracks in a given database was selected randomly and rotated randomly to reflect an isotropic emission. Afterward, deposited energy was divided between voxels based on step length in each voxel using a ray-tracing approach. The radial distribution of deposited energy was benchmarked against fully simulated MC calculations using GEANT4. The effect of the GEANT4 parameter StepMax on the accuracy and speed of the code was also investigated. In the case of alpha decay, primary alpha particles show the highest contribution (>99%) in deposited energy compared to their secondary particles. In most cases, protons act as the main secondary particles in the deposition of energy. However, for a lung phantom, using a range cutoff parameter of 10µm on primary alpha particles yields a higher contribution of secondary electrons than protons. Differences between deposited energy calculated by PMC and fully simulated MC are within 2% for all alpha and beta emitters in homogeneous and heterogeneous phantoms. Additionally, statistical uncertainties are less than 1% for voxels with doses higher than 5% of the maximum dose. Moreover, optimization of the parameter StepMax is necessary to achieve the best tradeoff between code accuracy and speed. The PMC code shows good performance for dose calculations deposited by alpha and beta emitters. As a stand-alone algorithm, it is suitable to be integrated into clinical treatment planning systems.

Emission of high-energy alpha particles in nuclear reactions of 48Ca and 56Fe ions on 181Ta and 238U targets

The results of experiments on measuring the energy spectra of alpha particles in reactions with heavy ions are presented. The measurements were performed using the high-resolution magnetic analyzer MAVR with beams of 48Ca (280 MeV) and 56Fe (320 and 400 MeV) on 181Ta and 238U targets at an angle of 0°. A strong dependence of the double differential cross sections for production of alpha particles on the atomic number of the target nucleus was observed, which indicates that fast alpha particles are mainly emitted from the target nucleus; this conclusion was also confirmed by calculations within the time-dependent Schrödinger equation approach. An analysis of the obtained experimental data was carried out within the model of moving sources modified to consider the kinematic limits for two-body and three-body exit channels.

Fast Charged Particles in the Interaction of {}^{{56}}Fe with Be, Ta, and U Nuclei at an Energy of 400 MeV

The energy spectra of alpha particles emitted at an angle of 0{}^{circ} in the interaction of 400-MeV {}^{56}Fe ions with {}^{238}U, {}^{181}Ta, and {}^{9}Be targets were measured by means of a high-resolution magnetic analyzer (MAVR, which is the acronym of the Russian name of this setup). The energy spectra of charged particles ranging from Li to Ne were also measured. The experimental data obtained in this way indicate that the emission of alpha particles is a dominant process in the above reactions. Particles of high energy, up to those in the vicinity of the so-called kinematical limit for two-body reactions, were observed with a rather high yield. The sensitivity of the experimental procedure that employed the aforementioned magnetic analyzer made it possible to observe events characterized by cross-section values smaller by six to eight orders of magnitude than that at the maximum of the spectrum. The cross section for the production of light particles is shown to be dependent on their binding energy in the target. The experimental data obtained in this study were analyzed with aid of the moving-source model.

Alpha particle detector with planar double Schottky contacts directly fabricated on semi-insulating GaN:Fe template* *Project supported by the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK20190302 and BK20201253).

Alpha particle radiation detectors with planar double Schottky contacts (DSC) are directly fabricated on 5-μm-thick epitaxial semi-insulating (SI) GaN:Fe film with resistivity higher than 1 × 108 Ω ⋅cm. Under 10 V bias, the detector exhibits a low dark current of less than 5.0 × 10−11 A at room-temperature, which increases at higher temperatures. Linear behavior in the semi-log reverse current–voltage plot suggests that Poole–Frenkel emission is the dominant carrier leakage mechanism at high bias. Distinct double-peak characteristics are observed in the energy spectrum of alpha particles regardless of bias voltage. The energy resolution of the SI-GaN based detector is determined to be ∼ 8.6% at the deposited energy of 1.209 MeV with a charge collection efficiency of ∼ 81.7%. At a higher temperature of 90 °C, the measured full width at half maximum (FWHM) rises to 235 keV with no shift of energy peak position, which proves that the GaN detector has potential to work stably in high temperature environment. This study provides a possible route to fabricate the low cost GaN-based alpha particle detector with reasonable performance.

Energy Spectra of Alpha Particles in the Interaction of $${}^{{56}}$$Fe Nuclei with Tantalum and Uranium Nuclei at an Energy of 320 MeV

The differential cross sections for alpha-particle emission at an angle of 0 $${}^{\circ}$$ in the reactions induced by a 6-MeV/nucleon $${}^{56}$$ Fe beams incident to $${}^{238}$$ U and $${}^{181}$$ Ta targets were measured versus the alpha-particle energy by means of a high-resolution magnetic analyzer (MAVR setup). The resulting spectra were found to contain fast alpha particles of energy corresponding to the two- and three-body exit reaction channels, including alpha particles of energy close to the two-body kinematical limit. The data obtained in this experiment were analyzed on the basis of the moving-source model. The emission of nonequilibrium alpha particles in the forward direction from the heavier target nucleus upon the complete or incomplete fusion of nuclei was revealed within the time-dependent quantum approach.

Analytical formulas of surface emitted energy spectra of alpha flat source

The analytical formulas of the surface emitted energy spectra of an alpha infinite flat source are derived, using the derived formulas of the distribution of residual range of alpha particles, considering the different thicknesses of the source and the absorbing layer. Utilizing these formulas, the typical residual range distributions and the energy spectra of alpha particles have been calculated and shown in figures. The variation tendency of the calculated spectrum is in good agreement with the measured spectrum.

Mechanisms of alpha particle induced soft errors in nanoscale static random access memories

In this paper, the Am-241 is used as an alpha particle radioactive source to investigate the soft error mechanism in 65-nm and 90-nm static random accessmemory (SRAM). Combining reverse analysis, TRIM and CREME-MC Monte Carlo simulation, the energy transport process, deposited energy spectrum and cross-section characteristics of alpha particles in the device are revealed. The results show that the soft error sensitivity of the 65-nm device is much higher than that of the 90-nm device, and no flipping polarity is found. According to the real-time measured soft error rate at an altitude of 4300 m in Tibetan Yangbajing area, the thermal neutron sensitivity and alpha particle soft error rate, the overall soft error rate of 65-nm SRAM used at sea level of Beijing city is 429 FIT/Mb, and the contribution from alpha particles is 70.63%. Based on the results of reverse analysis, a three-dimensional simulation model of the device is constructed to study the influence of the incident angle of alpha particles on the single event upset characteristics. It is found that the corresponding deposition energy value at the peak of the number of particles in the sensitive region decreases by 40% with the incident angle increasing from 0° to 60°. While the single event upset cross sectionincreases by 79% due to the apparent single event upset edge effect in a sensitive region of the 65-nm device.

Experimental investigation on nuclear reactions using a laser-accelerated proton and deuteron beam

We report an experimental investigation on nuclear reactions using an intense, ultra-short laser-accelerated proton and deuteron beam generated by the interaction of 25 fs, 150 TW Ti: sapphire laser pulse with normal thin foils and foils containing deuterium atoms. The production of a positron-emitting short-lived 11C radio-isotope from the interaction of protons and deuterium ions with a solid boron palette by means of 11B (p, n)11C and 10B (d, n)11C nuclear reactions was studied. The maximum radioactivity in the optimized laser irradiation condition was found to be 5.2 kBq per laser shot, which corresponds to ∼9 × 106 atoms of 11C isotopes using the 11B (p, n)11C reaction. The relative efficiency of 11C production using a proton and deuteron beam was also explored experimentally. About 30 % enhancement in 11C activity was observed with CD2 coated targets. It was also found that because of the relatively low deuteron energy threshold of the reaction 10B (d, n)11C, even the low energy part of the accelerated deuterons in the spectrum can be used for efficient 11C production. In the same setup, the proton-induced fusion reaction in the boron target (p + 5B11 ⇒ 3α + 8.7 MeV) was also studied. The resultant fusion yield and alpha particle energy spectrum was measured.

Estimation of (n, p) and (n, α) Cross Section of Radionuclide 60Co for Fusion Technology Applications

For fusion application, there is a high demand for nuclear data for long-lived radionuclides produced in a neutron environment. Cobolt-60 (t1/2 = 5.3 years) is one of the radionuclides produced in a large amount inside the fusion reactor via different pathways. In this context, the excitation function of 60Co(n, p) and 60Co(n, α) reaction from threshold to 20 MeV has been calculated using TALYS-1.6 in the framework of the Hauser Feshbach statistical model along with preequilibrium effects. Outgoing (proton and alpha) particle energy spectra (dσ/dEp, dσ/dEα) and double-differential cross section (d2σ/dE dΩ) has also been estimated at 14 MeV incident neutron energy. Optimized input parameters used during the model calculation were determined by fitting the (n, p) and (n, α) cross sections to the experimental data for the adjacent stable nuclide 59Co. The activation analysis has also been carried out for 1 kg of stainless steel (SS316) using FISPACT-2007.

Simulation of the response of a PIPS detector using GEANT4 code

The main objective of this work is to simulate a PIPS (Passivated Implanted Planar Silicon) detector response by Monte Carlo method and its validation with experimental results. Specifically, we have calculated via simulation the counting efficiency and the energy resolution of a PIPS detector. In order to do this, we have developed a Geant4 application that includes the most relevant physics processes, the geometry, composition and radioactive content of the sample, and the geometry of the PIPS detector and the vacuum chamber. However, some parameters involved in the Monte Carlo simulation are unknown (detector dead layer or sample thickness), and it was mandatory to estimate them through comparisons between experimental and calculated detector responses in order to obtain an accurate simulation of the PIPS detector.To show the validity of the simulated results, we present a comparison of the simulated alpha particle energy spectrum with the experimental one from a uranium dioxide pellet.

Flexible alpha camera for detecting plutonium contamination

We developed a new imaging detector called flexible alpha camera that can identify Pu contamination in narrow spaces at work sites. The thickness of the flexible alpha camera is only ∼1/5th that of the ZnS(Ag) scintillation detector which is commonly used for detecting Pu contamination, and its efficiency in the 4-pi direction is 42.7% for 5.5-MeV alpha particles. The minimal detectable activity (MDA) is 0.014 Bq measured in 30 min. Four types of PuO2 samples, taken from a duct, bag-in/bag-out port, glovebox glove, and vinyl sheet, were measured by the flexible alpha camera. In a two-dimensional distribution of alpha particles, PuO2 was identified automatically using the “AnalyzeParticle” function in the ImageJ plugin, and its activity was evaluated. When acquisition time increased from 10 min to 30 min, a Pu spot with low activity was identified. To verify the measurement in narrow space, a fume hood to which a PuO2 particle was attached was measured using the flexible alpha camera. Since the flexible alpha camera has the thin-thickness of 12 mm and can obtain two-dimensional distribution and energy spectrum of alpha particles, it is effective for detecting Pu contamination in narrow spaces of equipment.

Bulk GaN alpha-particle detector with large depletion region and improved energy resolution

An alpha-particle detector was fabricated using a freestanding n-type bulk GaN wafer with a Au/Ni/GaN sandwich Schottky structure. Current–voltage measurements at room temperature revealed a Schottky contact with a leakage current of 7.53±0.3nA at a reverse bias of 200V. The detector had a large depletion depth that can capture much of the energy from 5.486MeV alpha particles emitted from a 241Am source. The resolution of its alpha-particle energy spectrum was improved to 2.2±0.2% at 5.486MeV under a bias of 550V. This superior resolution was attributed to the shortening of the carrier transit time and the large energy deposition within the large depletion depth, i.e., 27µm at −550V, which all resulted in a more complete charge collection. A model developed using the ATLAS simulation framework from Silvaco Inc. was employed to study the charge collection process. The simulation results were found to agree closely with the experimental results. This detector will be beneficial for research at neutron scattering facilities, the International Thermonuclear Experimental Reactor, and the Large Hadron Collider, among other institutions, where the Si-based charged particle detectors could be quickly degraded in an intense radiation field.

Determination of the thickness of an electrodeposited thorium film with SiC alpha detectors

Alpha spectroscopy can be used to quantify actinide (e.g., U, Pu) concentration in a molten salt electrorefining environment. One could electroplate actinide samples directly onto a semiconductor alpha particle detector to obtain representative isotopic concentrations from a measured alpha particle energy spectrum. In this work, we fabricated a SiC Schottky device that can be partially biased to a depletion depth of 8.8 µm that is able to measure the energy spectrum of 4.012 MeV alpha particles emitted from a thorium film with a thickness. We also present a method in calculating the thickness of a medium thick alpha source with a dE/dx detector.

Development of the MICROMEGAS detector for measuring the energy spectrum of alpha particles by using a 241Am source

We have developed MICROMEGAS (MICRO MEsh GASeous) detectors for detecting {\alpha} particles emitted from an 241-Am standard source. The voltage applied to the ionization region of the detector is optimized for stable operation at room temperature and atmospheric pressure. The energy of {\alpha} particles from the 241-Am source can be varied by changing the flight path of the {\alpha} particle from the 241 Am source. The channel numbers of the experimentally-measured pulse peak positions for different energies of the {\alpha} particles are associated with the energies deposited by the alpha particles in the ionization region of the detector as calculated by using GEANT4 simulations; thus, the energy calibration of the MICROMEGAS detector for {\alpha} particles is done. For the energy calibration, the thickness of the ionization region is adjusted so that {\alpha} particles may completely stop in the ionization region and their kinetic energies are fully deposited in the region. The efficiency of our MICROMEGAS detector for {\alpha} particles under the present conditions is found to be ~ 97.3 %.

Monte Carlo simulation of semiconductor detector response to 222Rn and 220Rn environments

A new electronic radon/thoron monitor employing semiconductor detectors based on a passive diffusion chamber design has been recently developed at the Helmholtz Zentrum München (HMGU). This device allows for acquisition of alpha particle energy spectra, in order to distinguish alpha particles originating from radon and radon progeny decays, as well as those originating from thoron and its progeny decays. A Monte-Carlo application is described which uses the Geant4 toolkit to simulate these alpha particle spectra. Reasonable agreement between measured and simulated spectra were obtained for both 220Rn and 222Rn, in the energy range between 1 and 10 MeV. Measured calibration factors could be reproduced by the simulation, given the uncertainties involved in the measurement and simulation. The simulated alpha particle spectra can now be used to interpret spectra measured in mixed radon/thoron atmospheres. The results agreed well with measurements performed in both radon and thoron gas environments. It is concluded that the developed simulation allows for an accurate prediction of calibration factors and alpha particle energy spectra.

On the analytic estimation of radioactive contamination from degraded alphas

The high energy spectrum of alpha particles emitted from a single isotope uniformly contaminating a bulk solid has a flat energy spectrum with a high end cutoff energy equal to the maximal alpha kinetic energy (Tα) of the decay. In this flat region of the spectrum, we show the surface rate rb (Bq keV−1cm−2) arising from a bulk alpha contamination ρb (Bq cm−3) from a single isotope is given by rb =ρb Δ R/ 4 Δ E , where Δ E = E1−E2>0 is the energy interval considered (keV) in the flat region of the spectrum and Δ R = R2−R1, where R2 (R1) is the amount of the bulk material (cm) necessary to degrade the energy of the alpha from Tα to E2 (E1). We compare our calculation to a rate measurement of alphas from 147Sm, (15.32 ± 0.03% of Sm(nat) and half life of (1.06 ± 0.01)× 1011 yr [1]), and find good agreement, with the ratio between prediction to measurement of 100.2%± 1.6% (stat)± 2.1% (sys). We derive the condition for the flat spectrum, and also calculate the relationship between the decay rate measured at the surface for a [near] surface contamination with an exponential dependence on depth and a second case of an alpha source with a thin overcoat. While there is excellent agreement between our implementation of the sophisticated Monte Carlo program SRIM [2] and our intuitive model in all cases, both fail to describe the measured energy distribution of a 148Gd alpha source with a thin (∼200μg cm−2) Au overcoat. We discuss possible origins of the disagreement and suggest avenues for future study.