Low-energy Protons Research Articles

Analysis of displacement damage mechanism and simulation proton irradiation on GaAs

GaAs is an important material for preparing power supply for space vehicles, satellites, and space systems. To study the displacement damage of GaAs material caused by protons in the space environment, in this article, the Monte Carlo software Geant4 was used to simulate the transport process of space protons in GaAs; calculate the non-ionizing energy loss (NIEL) of protons with different energies; and obtain the species, energy range, and proportion of primary knock-on atom produced by proton irradiation with different energies. The results show that with the increase in the incident proton energy, the probability of elastic collision decreases and the probability of inelastic collision increases. The main source of displacement damage changes from elastic collision to inelastic collision. The radiation damage of low energy protons is serious at the end of the range, while that of high energy protons is serious at the beginning and end of the range. With the increase in the proton energy, the number of displaced atoms increases and the NIEL changes slowly. This provides a theoretical reference for the reliable operation of spacecraft.

Visible radiophotoluminescence of colour centres in lithium fluoride: from lasers to versatile radiation sensors

The peculiar photoluminescence characteristics of radiation-induced colour centres in lithium fluoride (LiF), well known for applications in optically-pumped tuneable lasers and broad-band miniaturised light-emitting photonic devices operating at room-temperature, are under exploitation in passive imaging detectors and dosimeters based on visible radiophotoluminescence in LiF crystals and polycrystalline thin films. Their high intrinsic spatial resolution, wide dynamic range and large field of view, combined with easy handling, ambient-light operation and no development need, allow to successfully extend their use from X-ray imaging to proton-beam advanced diagnostics and dosimetry, even at those low dose values that are typical of hadrontherapy. After exposure, the latent images stored in LiF as local formations of F2 and F3 + aggregate defects are read with an optical fluorescence microscope under illumination in the blue spectral range. Their visible emission intensity was found to be linearly proportional to the dose over at least three orders of magnitude, so that bi-dimensional LiF solid-state dosimeters based on spectrally-integrated radiophotoluminescence reading can be envisaged. Taking advantage of the low thickness of LiF thin films, transversal proton beam dose mapping was demonstrated at low proton energies, even at high doses. Recent results and advances concerning LiF crystals and polycrystalline thin film characterisation in the linearity range are presented and discussed with the aim of highlighting challenges related to increasing the LiF film detector radiation sensitivity to both particles (protons) and photons (X-rays), although therapeutic dose values typical of clinical radiotherapy are still a big challenge.

Cosmic-ray-induced H2 line emission

Context. It has been proposed that H2 near-infrared lines may be excited by cosmic rays and thus allow for a determination of the cosmic-ray ionization rate in dense gas. One-dimensional models show that measuring both the H2 gas column density and H2 line intensity enables a constraint on the cosmic-ray ionization rate as well as on the spectral slope of low-energy cosmic-ray protons in the interstellar medium. Aims. We aim to investigate the impact of certain assumptions regarding the H2 chemical models and interstellar medium density distributions on the emission of cosmic-ray-induced H2 emission lines. This is of particular importance for utilizing observations of these lines with the James Webb Space Telescope to constrain the cosmic-ray ionization rate. Methods. We compare the predicted emission from cosmic-ray-induced, rovibrationally excited H2 emission lines for different one-and three-dimensional models with varying assumptions regarding the gas chemistry and density distribution. Results. We find that the model predictions of the H2 line intensities for the (1-0)S(0), (1-0)Q(2), (1-0)O(2), and (1-0)O(4) transitions at 2.22, 2.41, 2.63, and 3.00 μm, respectively, are relatively independent of the astro-chemical model and the gas density distribution when compared against the H2 column density, making them robust tracers of the cosmic-ray ionization rate. Conclusions. We recommend the use of rovibrational H2 line emission in combination with estimations of the cloud’s H2 column density to constrain the ionization rate and the spectrum of low-energy cosmic rays.

First results for the pLGAD sensor for low-penetrating particles

Silicon sensors are the go-to technology for high-precision sensors in particle physics. But only recently low-noise silicon sensors with internal amplification became available. The so-called Low Gain Avalanche Detector (LGAD) sensors have been developed for applications in High Energy Physics, but lack two characteristics needed for the measurement of low-energy protons (<60keV): a thin entrance window (in the order of tens of nm) and the efficient amplification of signals created near the sensor’s surface (in a depth below 1µm).In this paper we present the so-called proton Low Gain Avalanche Detector (pLGAD) sensor concept and some results from characterisation of the first prototypes of the sensor. The pLGAD is specifically designed to detect low-energy protons, and other low-penetrating particles. It will have a higher detection efficiency than non-silicon technologies, and promises to be a lot cheaper and easier to operate than competing silicon technologies.

Proton Spectra for the Interplanetary Space Derived From Different Environmental Models

Knowledge about the space radiation environment is crucial for the design and selection of materials and components used for space applications. This environment is characterized not only by the Sun’s electromagnetic radiation but also by charged particles categorized into solar wind, solar energetic particles (SEP) and galactic cosmic rays (GCR). Especially for material engineering and qualification testing, differential and integral spectra for particle energies ranging from keVs to GeVs are required. Up to now, a wide variety of models is available, whereas it is difficult to keep the overview. Although, e.g., the European Cooperation for Space Standardization (ECSS) standard includes instructions on how to investigate particle radiation, it does not provide an overall view. This paper shall support those in need of a comprehensive overview and provide comprehensive information about proton radiation spectra that can potentially be of use for space engineering tasks ranging from mission analysis to material and component design as well as qualification testing. The publicly accessible platforms OLTARIS, SPENVIS, and OMERE were examined for available proton spectra to be used. Exemplary, the particle radiation of solar cycle 23 is considered, which comprehends the years 1996–2008. A common drawback of the available models is their restriction to the MeV-range. Particularly when materials are directly exposed to the space environment, low energetic particles, specifically, the keV-range, are of high interest, since these particle transfer all their energy to the material. Therefore, additional data sources were used in order to include the usually neglected low energy protons into the derived spectrum. The data was transferred to common set of units and eventually could be compared and merged together. This includes a comparison of the most common models, incorporating data foundation, applicability, and accessibility. As a result, extensive and continues spectra are fitted that take all different models with its different energies and fluxes into account. Each covered year is represented by a fitted spectrum including confidence level as applicable. For solar active and quite times spectra are provided.

In-depth investigation of low-energy proton irradiation effect on the structural and photoresponse properties of ε-Ga2O3 thin films

Ga2O3 possesses an ultra-wide bandgap (∼4.9 eV) and an extremely large breakdown field strength (∼8 MV/cm), which promises extraordinary application potential in power electronics and ultraviolet optoelectronics. With the demand for highly durable devices in harsh environments such as in low earth orbit spacecraft, in-depth understanding of the particle radiation effect on the structural and performance degradation of the device is desired. In this work, we employ 150 keV low energy proton with intensity up to 5 × 1015 dose to irradiate the epitaxial ε-Ga2O3 thin films. The characterization of the structural and optical properties shows no detectable variations in lattice structure and optical transmission. In addition, with increasing irradiation dosage, a decrease of Ga3+ population and an increase of the concentration of oxygen vacancies are confirmed by X-ray photoemission spectroscopy. Photoresponse measurements further illustrate that, despite of a mild degradation in the photodetector performance, the device still shows a high photoresponsivity of 2.52 × 10-3 A/W and a large photo-to-dark current ratio over 103. Our work reveals that ε-Ga2O3 exhibits excellent radiation hardness under low-energy proton irradiation conditions and highlights the potential for operational optoelectronics in extreme environment.

Comparison of pencil beam and Monte Carlo calculations with ion chamber array measurements for patient-specific quality assurance

ObjectiveTo determine under what conditions and criteria comparisons between calculations made with the current clinical treatment planning system (Syngo) and an in-house built TPS (TIMPS) would allow skipping of in-beam portal-specific measurements. MethodsMeasurements were made with an array of 24 ion chambers in a water phantom for 227 proton and 313 carbon ion portals with and without a range shifter (RS). These measurements were compared with calculations performed with Syngo and TIMPS using metrics of average dose difference and Gamma index. ResultsFor proton portals without RS, if a Gamma comparison between TIMPS and Syngo passed using criteria of 90% of tested points being within 3% and 3 ​mm, then 74% of measurements would agree with both TIMPS and Syngo. For proton portals with RS, more than 80% of measurements would agree with both calculations using the same criteria. For carbon ion portals without RS, if a Gamma evaluation between TIMPS and Syngo passed with criteria of 90% of tested points being within 2% and 2 ​mm, 85% of measurements would agree with both calculations. For carbon ion portals with RS, if a Gamma evaluation between TIMPS and Syngo passed with criteria of 90% of tested points being within 3% and 3 ​mm, 60% of measurements would agree with both calculations. ConclusionsBoth the pencil beam algorithm in Syngo and the FDC algorithm in TIMPS can provide accurate dose calculations in water for most clinical portals. For about 75% of portals, physicists can perform comparisons of calculations instead of phantom measurements to verify Syngo calculations thereby saving a large amount of beam time. There are some portals, however, such as for low-energy protons without RS and high-energy carbon ions, where agreement between the two calculations and measurements are not yet satisfactory to allow the elimination of all measurements.

Ocular proton therapy, pencil beam scanning high energy proton therapy or stereotactic radiotherapy for uveal melanoma; an in silico study

PurposeIn radiotherapy, the dose and volumes of the irradiated normal tissues is correlated to the complication rate. We assessed the performances of low-energy proton therapy (ocular PT) with eye-dedicated equipment, high energy PT with pencil-beam scanning (PBS) or CyberKnifeR -based stereotactic irradiation (SBRT). Material and methodsCT-based comparative dose distribution between external beam radiotherapy techniques was assessed using an anthropomorphic head phantom. The prescribed dose was 60Gy_RBE in 4 fractions to a typical posterior pole uveal melanoma. Clinically relevant structures were delineated, and doses were calculated using radiotherapy treatment planning softwares and measured using Gafchromic dosimetry films inserted at the ocular level. ResultsPrecision was significantly better with ocular PT than both PBS or SBRT in terms of beam penumbra (80%–20%: laterally 1.4 vs. ≥10mm, distally 0.8 vs. ≥2.5mm). Ocular PT duration was shorter, allowing eye gating and lid sparing more easily. Tumor was excellent with all modalities, but ocular PT resulted in more homogenous and conformal dose compared to PBS or SBRT. The maximal dose to ocular/orbital structures at risk was smaller and often null with ocular PT compared to other modalities. Mean dose to ocular/orbital structures was also lower with ocular PT. Structures like the lids and lacrimal punctum could be preserved with ocular PT using gaze orientation and lid retractors, which is easier to implement clinically than with the other modalities. The dose to distant organs was null with ocular PT and PBS, in contrast to SBRT. Conclusionsocular PT showed significantly improved beam penumbra, shorter treatment delivery time, better dose homogeneity, and reduced maximal/mean doses to critical ocular structures compared with other current external beam radiation modalities. Similar comparisons may be warranted for other tumor presentations.

Analyzing Scaled Reduced Precision Redundancy for Error Mitigation Under Proton Irradiation

Reduced precision redundancy (RPR) is an alternative to triple modular redundancy (TMR) that reduces the area overhead at the expense of minor accuracy loss in case of error. In this work, we propose a Scaled RPR approach for multistage circuits and analyze the error mitigation tradeoffs. As a case study, several fast Fourier transform designs were tested with low-energy protons and fault injection. Experimental results show that the proposed approach achieves error mitigation with good accuracy, while significantly reducing the area overhead with respect to a full precision TMR approach.

Characterising potential space suit textiles in proton beams using radiotherapy-based dosimetry

Four multi-layer textile samples for potential use in space suits, developed within the Planetary Exploration Textiles project of the European Space Agency, were exposed to a low energy proton beam, to characterise their effect on dose deposition in astronauts. Each textile stack contained all required layers for a potential space suit component. The influence of the textiles on proton beams was investigated using dosimetric equipment as utilised for medical purposes. The experiments were conducted at the synchrotron-based therapy and research centre MedAustron, Austria. To quantify the radiation characteristics, the water equivalent thickness of the fabrics was determined. A PEAKFINDERsystem (PTW, Freiburg, Germany) was positioned downstream of the textiles and the positions of the Bragg peaks were measured and compared to the range without any material in front. As reference values aluminium and lead plates were used and the results of the textiles were normalised to these materials. Furthermore, proton threshold energies for stopping protons in the suit materials were calculated. The position of the Bragg peak was shifted between 1.2mm to 2.6mm depending on the textile stacks. This corresponds to a proton threshold energy for the investigated stacks between 10–15MeV. The study showed that methods used in particle therapy are appropriate tools to quantify characteristics of space suit materials in proton beams. However, the effect of the investigated textiles on proton beams was comparable among the used fabrics.

Hybrid Lockstep Technique for Soft Error Mitigation

This work presents the evaluation of a new dual-core lockstep hybrid approach aimed to improve the fault tolerance in microprocessors. Our approach takes advantage of modern multicore processor resources to combine software-based lockstep with a custom hardware observer. The first is used to duplicate data and instruction flows; meanwhile, the second is in charge of the control-flow monitoring. The proposal has been implemented in a dual-core ARM microprocessor and validated with low-energy proton irradiation and emulated fault injection campaigns. The results show an improvement of one order of magnitude in the cross section of the benchmarks tested, even considering the worst case scenario.

Experiments on the Electron Impact Excitation of the 2s and 2p States of Hydrogen Atoms Confirm the Presence of Their Second Flavor as the Candidate for Dark Matter

For the excitation of the n = 2 states of hydrogen atoms due to electron impact, we compared the experimental and theoretical ratios of the cross-sections σ2s/σ2p. We found this theoretical ratio to be systematically higher than the corresponding experimental ratio by about 20%—far beyond the experimental error margins. We suggest that this discrepancy can be explained by the presence of the Second Flavor of Hydrogen Atoms (SFHA) in the experimental hydrogen gas. The explanation is based on the fact that, in the experiments, the cross-section σ2s was determined by using the quenching technique—by applying an electric field that mixed the 2s and 2p states, followed by the emission of the Lyman-alpha line from the 2p state. However, the SFHA only had the s-states, so the quenching technique would not count the excitation of the SFHA in the 2s state and, thus, lead to the underestimation of the cross-section σ2s. We estimates the share of the SFHA in the experimental hydrogen gas required for eliminating the above discrepancy and found this share to be about the same as the share of the usual hydrogen atoms. Thus, our results constitute the third proof from atomic experiments that the SFHA does exist, the first proof being related to the experimental distribution of the linear momentum in the ground state of hydrogen atoms, and the second proof being related to the experimental cross-section of charge exchange between hydrogen atoms and low-energy protons.

The Effects of Quantum Entanglement in Low-Energy Proton–Proton Scattering

The Effects of Quantum Entanglement in Low-Energy Proton–Proton Scattering

Countdown to perovskite space launch: Guidelines to performing relevant radiation-hardness experiments

<h2>Summary</h2> Perovskite photovoltaics (PVs) are under intensive development for promise in terrestrial energy production. Soon, the community will find out how much of that promise may become reality. Perovskites also open new opportunities for lower cost space power. However, radiation tolerance of space environments requires appropriate analysis of relevant devices irradiated under representative radiation conditions. We present guidelines designed to rigorously test the radiation tolerance of perovskite PVs. We review radiation conditions in common orbits, calculate nonionizing and ionizing energy losses (NIEL and IEL) for perovskites, and prioritize proton radiation for effective nuclear interactions. Low-energy protons (0.05–0.15 MeV) create a representative uniform damage profile, whereas higher energy protons (commonly used in ground-based evaluation) require significantly higher fluence to accumulate the equivalent displacement damage dose due to lower scattering probability. Furthermore, high-energy protons may "heal" devices through increased electronic ionization. These procedural guidelines differ from those used to test conventional semiconductors.

PD-0816 LET Quenching of EBT3 radiochromic films with low-energy protons

PD-0816 LET Quenching of EBT3 radiochromic films with low-energy protons

A Statistical Study of Pancake Pitch Angle Distribution of Low‐Energy Protons and Their Correlation With Magnetosonic Waves

AbstractWe performed a statistical study of the proton pancake pitch angle distributions (PADs) at the energy from 10 to 300 eV with the Helium Oxygen Proton Electron instrument on board the Van Allen Probes. The occurrence rate of low energy proton pancake PADs and their dependence on the energy, L shell, magnetic local time (MLT) and AL* index are analyzed. The results indicate that: (a) the occurrence rate of pancake PADs decreases as the proton energy increases; (b) under active geomagnetic activities (AL* &lt; −300 nT), pancake PADs preferentially occur in the dayside; (c) under weak geomagnetic activities (AL* &gt; −100 nT), the occurrence rate of pancake PADs has little dependence on MLT. We further discuss the contribution of magnetosonic (MS) waves on the formation of proton pancake PADs at low energy. The strong correlation between the occurrence of pancake PADs and the appearance of MS waves indicates that MS waves contribute to the formation of low energy proton pancake PADs. Moreover, the proton diffusion coefficients caused by MS waves suggest that MS waves can cause the proton heating at low energies in high density regions.

Absolute calibration of Fujifilm BAS-TR image plate response to laser driven protons up to 40 MeV.

Image plates (IPs) are a popular detector in the field of laser driven ion acceleration, owing to their high dynamic range and reusability. An absolute calibration of these detectors to laser-driven protons in the routinely produced tens of MeV energy range is, therefore, essential. In this paper, the response of Fujifilm BAS-TR IPs to 1-40MeV protons is calibrated by employing the detectors in high resolution Thomson parabola spectrometers in conjunction with a CR-39 nuclear track detector to determine absolute proton numbers. While CR-39 was placed in front of the image plate for lower energy protons, it was placed behind the image plate for energies above 10MeV using suitable metal filters sandwiched between the image plate and CR-39 to select specific energies. The measured response agrees well with previously reported calibrations as well as standard models of IP response, providing, for the first time, an absolute calibration over a large range of proton energies of relevance to current experiments.

In vivo production of fluorine-18 in a chicken egg tumor model of breast cancer for proton therapy range verification

Range verification of clinical protontherapy systems via positron-emission tomography (PET) is not a mature technology, suffering from two major issues: insufficient signal from low-energy protons in the Bragg peak area and biological washout of PET emitters. The use of contrast agents including 18O, 68Zn or 63Cu, isotopes with a high cross section for low-energy protons in nuclear reactions producing PET emitters, has been proposed to enhance the PET signal in the last millimeters of the proton path. However, it remains a challenge to achieve sufficient concentrations of these isotopes in the target volume. Here we investigate the possibilities of 18O-enriched water (18-W), a potential contrast agent that could be incorporated in large proportions in live tissues by replacing regular water. We hypothesize that 18-W could also mitigate the problem of biological washout, as PET (18F) isotopes created inside live cells would remain trapped in the form of fluoride anions (F-), allowing its signal to be detected even hours after irradiation. To test our hypothesis, we designed an experiment with two main goals: first, prove that 18-W can incorporate enough 18O into a living organism to produce a detectable signal from 18F after proton irradiation, and second, determine the amount of activity that remains trapped inside the cells. The experiment was performed on a chicken embryo chorioallantoic membrane tumor model of head and neck cancer. Seven eggs with visible tumors were infused with 18-W and irradiated with 8-MeV protons (range in water: 0.74 mm), equivalent to clinical protons at the end of particle range. The activity produced after irradiation was detected and quantified in a small-animal PET-CT scanner, and further studied by placing ex-vivo tumours in a gamma radiation detector. In the acquired images, specific activity of 18F (originating from 18-W) could be detected in the tumour area of the alive chicken embryo up to 9 h after irradiation, which confirms that low-energy protons can indeed produce a detectable PET signal if a suitable contrast agent is employed. Moreover, dynamic PET studies in two of the eggs evidenced a minimal effect of biological washout, with 68% retained specific 18F activity at 8 h after irradiation. Furthermore, ex-vivo analysis of 4 irradiated tumours showed that up to 3% of oxygen atoms in the targets were replaced by 18O from infused 18-W, and evidenced an entrapment of 59% for specific activity of 18F after washing, supporting our hypothesis that F- ions remain trapped within the cells. An infusion of 18-W can incorporate 18O in animal tissues by replacing regular water inside cells, producing a PET signal when irradiated with low-energy protons that could be used for range verification in protontherapy. 18F produced inside cells remains entrapped and suffers from minimal biological washout, allowing for a sharper localization with longer PET acquisitions. Further studies must evaluate the feasibility of this technique in dosimetric conditions closer to clinical practice, in order to define potential protocols for its use in patients.

Electronic stopping power and electronic energy-loss mechanism for a low-energy ion in TiN under channeling conditions

The electronic stopping power of a low-energy proton in a crystalline TiN film is investigated by computer simulation based on the time-dependent density-functional theory. The calculated results show that the electronic stopping power of the small impact parameter coincides with the experimental data. By evaluating the channeling electronic density and the stopping force in different channels, the direction dependence of the electronic stopping power is explored and revealed. Along the $\ensuremath{\langle}110\ensuremath{\rangle}$ channel, the electronic stopping power of the proton is lower than that of the $\ensuremath{\langle}100\ensuremath{\rangle}$ and $\ensuremath{\langle}111\ensuremath{\rangle}$ channels; this trend is mainly attributed to the discrepancy in the channeling electronic density. In addition, our research gives evidence that the threshold velocity ${v}_{th}=0.1294\phantom{\rule{0.16em}{0ex}}\text{a.u.}$ is closely related to the indirect band gap. That result suggests that only the valence band's electrons across the band gap can contribute to the electronic energy dissipation; therefore, we discuss that the defect state induced in the gap by the passing ion serves like an elevator ferrying the valence-band electrons across the indirect band gap. Last, we investigate the charge accumulation and depletion as an energy-loss model by intuitive charge-density difference. Furthermore, the intensity of the chemical bond between the projectile and the host atoms around the channel is indirectly investigated and analyzed by obtaining the amplitude of the electron localization function. The shortening and elongation of the chemical bond are deemed a mechanism of the electronic energy loss in the process of the ion-solid interaction, which can contribute to the electronic stopping power. These results supply reference data for the application of the excellent material TiN in ion-beam irradiation.

Optical and thermal luminescence efficiencies of BeO exposed to low-energy protons and carbon ions

Optically stimulated luminescence (OSL) and thermoluminescence (TL) are well-described phenomena utilized to measure the absorbed dose of crystalline materials. The techniques are used to monitor low linear energy transfer (LET) radiation (β, γ) as well as high-LET heavy charged particles (HCPs). Detector efficiency ƞdet, defined as the ratio of the luminescence per unit dose from a non-reference radiation field compared to the identical quantity from the reference field, is particle and energy dependent. The responses of BeO ceramics exposed to low-energy HCPs were investigated in this work. Dosimeters were bombarded with 1, 2, and 4 MeV protons, as well as 2 and 4 MeV carbon ions; these radiation qualities constitute a mean LET range of 37.6 keV/μm - 628 keV/μm and were realized using the 2 MV tandem Pelletron particle accelerator at East Carolina University. Each dosimeter was calibrated using a dose response constructed with a90Sr/90Y β source, which was calibrated against a137Cs γ source. This enabled ƞdet to be calculated. It was observed that optical and thermal signal shape and magnitude depend on the mean LET. Furthermore, thermal efficiencies are significantly higher than optical efficiencies for all ions investigated.