Low-energy Protons Research Articles

On the Nature of the Energy-dependent Morphology of the Composite Multi-TeV Gamma-Ray Source J1702-204

HESS J1702-420 is a multi-TeV gamma-ray source with an unusual energy-dependent morphology. The recent H.E.S.S. observations suggest that the emission is well described by a combination of the point-like HESS J1702-420A (dominating at highest energies, ≳30 TeV) and diffuse (∼0.°3) HESS J1702-420B (dominating below ≲5 TeV) sources with very hard (Γ ∼ 1.5) and soft (Γ ∼ 2.6) power-law spectra, respectively. Here, we propose a model that postulates that the proton accelerator is located at the position of HESS J1702-420A and is embedded into a dense molecular cloud that coincides with HESS J1702-420B. In the proposed model, the very-high-energy radiation of HESS J1702-420 is explained by pion-decay emission from the continuously injected relativistic protons propagating through a dense cloud. The energy-dependent morphology is defined by the diffusive nature of the low-energy proton propagation, transiting sharply to (quasi) ballistic propagation at higher energies. Adopting a strong energy dependence of the diffusion coefficient, D ∝ E β with β ≥ 1, we argue that HESS J1702-420 as a system of two gamma-ray sources is the result of the propagation effect. Protons injected by a single accelerator at a rate can reasonably reproduce the morphology and fluxes of the two gamma-ray components.

Two proton emission and other exotic decays in the 48Ni region with ACTAR TPC

Since the first indirect measurements of the two proton radioactivity in 2002 [1], some theoretical descriptions have been able to reproduce experimental results until the 2-proton radioactivity was established for 67Kr at RIKEN [2], with a lifetime about 20 times lower than expected. New theory inputs have recently been developed [3][4], predicting angular distributions of the emitted protons for some of the two proton emitters, that need to be confirmed experimentally. An experiment at GANIL/LISE3 facility was performed in May 2021 aiming to produce one of the 2 proton emitters (48Ni) and measure the angular distribution of the emitted protons. We used the ACTAR TPC detector to implant the ions and perform the tracking of their proton decays. In addition, other exotic nuclei in the 48Ni region were produced. For several of them we have found a first evidence of exotic decays such as β delayed 3- and 2-proton emission or low energy proton branches for β delayed single proton emission. The analysis of this decays will provide helpful experimental information about the structure and the partial decay schemes of these unstable nuclei.

Investigating the hard X-ray production via proton spallation on different materials to detect elements.

Various atomic and nuclear methods use hard (high-energy) X-rays to detect elements. The current study aims to investigate the hard X-ray production rate via high-energy proton beam irradiation of various materials. For which, appropriate conditions for producing X-rays were established. The MCNPX code, based on the Monte Carlo method, was used for simulation. Protons with energies up to 1650 MeV were irradiated on various materials such as carbon, lithium, lead, nickel, salt, and soil, where the resulting X-ray spectra were extracted. The production of X-rays in lead was observed to increase 16 times, with the gain reaching 0.18 as the proton energy increases from 100 MeV to 1650 MeV. Comparatively, salt is a good candidate among the lightweight elements to produce X-rays at a low proton energy of 30 MeV with a production gain of 0.03. Therefore, it is suggested to irradiate the NaCl target with 30 MeV proton to produce X-rays in the 0-2 MeV range.

Improved energy spread in the radiation pressure acceleration of protons with a linearly polarized laser.

Degradation in the energy spread of accelerated protons due to the transverse instability induced transparency is one of the critical issues in the laser-driven radiation pressure acceleration (RPA) scheme. This issue is more severe for linearly polarized lasers due to enhanced heating of electrons. Therefore, in spite of being experimentally challenging, most of the numerical studies are performed with circularly polarized lasers. In this work, through particle-in-cell simulations, we demonstrate a significant improvement in the energy spread of the accelerated protons when a multilayered target is irradiated by a linearly polarized laser. This multilayered target consists of a near-critical-density (NCD) layer, sandwiched between a thick metallic foil and a thin RPA target. The role of the NCD target is to suppress the laser transparency to increase the coupling of laser momentum to the RPA protons. On the other hand, the metallic foil utilizes the kinetic energy of the escaping fast electrons to form an electrostatic sheath to filter the low-energy RPA protons. This results in significant improvement in the accelerated proton spectrum, even with a linearly polarized laser.

Evaluation of the Single-Event-Upset Vulnerability for Low-Energy Protons at the 7- and 5-nm Bulk FinFET Nodes

Upsets due to low-energy protons are a concern for highly scaled technology nodes as critical charges for storage cells continue to decrease. This work evaluates the SEU vulnerability of D-FF and SRAM designs at the 7-nm and 5-nm bulk FinFET nodes. D-FF designs at the 5-nm node have single-event upset (SEU) cross-sections that are an order of magnitude greater than that of the 7-nm node due to unbalanced decreases in critical charge and collected charge. Upsets were observed for a wider range of proton energies for the 5-nm node than the 7-nm node D-FFs due to the decreases in critical charge and changes in fin geometry with scaling. Despite its smaller cell size, the single-port SRAM design was more susceptible than the two-port SRAM design due to the lower critical charge. Multi-cell upsets due to lower-energy protons were observed for the first time for SRAM designs at the 5-nm node. The results of this study indicate that designers will need to be mindful of SEUs for environments with significant fluxes of low-energy protons.

An Analysis of the Significance of the 14N(n, p) 14C Reaction for Single-Event Upsets Induced by Thermal Neutrons in SRAMs

The thermal neutron threat to the reliability of electronic devices caused by <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B capture is a recognized issue that prompted changes in the manufacturing process of electronic devices with the aim of limiting as much as possible the presence of this isotope nearby device sensitive volumes. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> N can also capture thermal neutrons and release low-energy protons (through the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> N(n,p) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> C reaction) that have high enough linear energy transfer to cause single-event upsets (SEU). Typically, nitrogen is used in thin barrier layers made of TaN or TiN or even as insulator in the form of Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> . Numerical simulations on sensitive volumes calibrated on proton and ion experimental data and with an accurate description of the metallization layer on top of the sensitive region show that the presence of nitrogen in these thin barrier layers can be enough to justify the experimentally observed thermal neutron SEU cross section for a static random access memory sensitive to low-energy protons. Nevertheless, the expected SEU cross section from thermal neutrons is usually a few orders of magnitude lower than that of high-energy particles, therefore, not representing an important threat in atmospheric applications. At the same time, for high-energy accelerators, the contribution to the total soft error rate could become substantial, though easy to handle by margins.

Observation of proton modulations in laser–solid interaction

We report on an experimental investigation into proton acceleration from the interaction of an intense laser pulse, with an intensity of about 1020 W cm−2, with a thin foil of aluminum, titanium and gold of thickness 2 µm. Protons are accelerated via the TNSA mechanism from the rear surface of the target and, in addition, protons accelerated from the front surface are also detected on the radio chromic films. Hollow proton rings could be seen on the radio chromic films, corresponding to 1–3 MeV protons. The protons from the front surface are driven into the target and directed towards the rear side of the target by the Kilotesla magnetic fields generated from the laser plasma. 2D particle-in-cell simulations predict an increase in the flux of lower energy protons similar to experimental observations and also show strong magnetic field structures in the laser–target interaction region.

Beam dynamic design and study of a linac with variable output energy for an AB-BNCT facility

The Accelerator-based Boron Neutron Capture Therapy (AB-BNCT) is being established worldwide as a future modality to start an era of in-hospital facilities. The most popular reaction for AB-BNCT is 7Li(p, n)7Be and high-flux neutron beams can be produced by bombarding lithium targets with low-energy proton beams. We chose the combined acceleration structure of Radio Frequency Quadrupole linac (RFQ) and Cross-bar H-mode DTL (CH-DTL) considering the compactness of the structure and the adjustment of output energy. The CW proton beam could be accelerated to 1.8 MeV by one RFQ cavity, and then to the final energy by one CH-DTL cavity. The output beam energy can be adjusted in the range of 2.2 MeV to 3.0 MeV with small beam loss and high beam quality, which could be achieved by controlling the feed power and RF phase of the CH-DTL. The variation of beam energy can meet requirements of the BNCT in treating tumors of different depths without adjusting structure of beam shaping assembly (BSA). The beam dynamics of the RFQ and DTL were completed to meet all requirements and the energy stability and adjustment method of output beam were investigated. In addition, we also performed the start-to-end beam tracking and error sensitivity analysis at last.

High-energy dipole scattering amplitude from evolution of low-energy proton light-cone wave functions

High-energy dipole scattering amplitude from evolution of low-energy proton light-cone wave functions

Gain measurements on NLGAD detectors

In the last few years, Low Gain Avalanche Detectors (LGAD) have demonstrated their outstanding performance when detecting high-energy charged particles. However, due to the difference in the multiplication mechanism for holes and electrons, the detection performance for low penetrating particles (e.g low-energy protons or soft x-rays) is significantly reduced. A novel design of an LGAD detector, the NLGAD, was designed and fabricated at CNM to overcome this drawback. A qualitative description of the NLGAD concept is presented in this work, along with gain response measurements of the first prototypes under visible light of 660 nm and 15 keV x-rays. Additionally, a review of the gain response under visible light of 404 nm and IR light of 1064 nm, previously studied, is also evaluated in this work. The results demonstrate that the NLGAD concept has the potential to detect low penetrating particles.

Energy-Dependent Impact of Proton Irradiation on 4H-SiC Schottky Diodes

In this work, the impact of 200 MeV proton irradiation at a fluence of 6 × 1012 cm−2 on the forward characteristics and the breakdown behaviour of nickel (Ni) and titanium (Ti) Schottky barrier diodes is explored. An improvement in the ideality factor, reduction in the threshold voltage, and an increase in the breakdown voltage is observed post irradiation. Point defects induced by the irradiation are likely responsible for the observed effects. Deep Level transient Spectroscopy (DLTS) measurements were performed on the irradiated Schottky diodes to analyse the defects created during the irradiation and gauge their potential role in changing the diode behavior. The defects induced by the high-energy protons were compared to those formed by low-energy proton irradiation at 1.8 MeV to a fluence of 1 × 1012 cm−2. Finally, consecutive DLTS measurements were performed after a series of reverse bias anneals at low temperatures from 350-700 K to explore the annealing behaviour of the defects induced by the proton irradiations.

TexAT detector upgrade for 14O([formula omitted])17F cross section measurement

A direct cross-section measurement of the 14O(α,p)17F reaction is important to understand the light curves of x-ray bursts. The measurement will be performed using the Texas Active Target TPC version 2 (TexAT_v2). The TexAT_v2 aims at measuring lower energy protons from the reaction than the original TexAT. Newly developed silicon and CsI(Tl) detector arrays are added at the left, right and bottom of a modified field cage to increase its detection efficiency. This paper describes the overall specifications and two commissioning experiments performed at Texas A&M University.

Bragg Curve Detection of Low-Energy Protons by Radiophotoluminescence Imaging in Lithium Fluoride Thin Films.

Lithium fluoride (LiF) crystals and thin films are utilized as radiation detectors for energy diagnostics of proton beams. This is achieved by analyzing the Bragg curves in LiF obtained by imaging the radiophotoluminescence of color centers created by protons. In LiF crystals, the Bragg peak depth increases superlinearly with the particle energy. A previous study has shown that, when 35 MeV protons impinge at grazing incidence onto LiF films deposited on Si(100) substrates, the Bragg peak in the films is located at the depth where it would be found in Si rather than in LiF due to multiple Coulomb scattering. In this paper, Monte Carlo simulations of proton irradiations in the 1-8 MeV energy range are performed and compared to experimental Bragg curves in optically transparent LiF films on Si(100) substrates. Our study focuses on this energy range because, as energy increases, the Bragg peak gradually shifts from the depth in LiF to that in Si. The impact of grazing incidence angle, LiF packing density, and film thickness on shaping the Bragg curve in the film is examined. At energies higher than 8 MeV, all these quantities must be considered, although the effect of packing density plays a minor role.

Development of an external PIGE method using nitrogen from atmospheric air as external beam current normalizer and its application to nondestructive quantification of total boron mass fraction in boron containing neutron absorbers

Beam current monitoring and normalization is a very important task in ion beam analysis experiments. Compared to current monitoring by conventional method, in situ or external beam current normalization is attractive in Particle Induced Gamma-ray Emission (PIGE), which involves simultaneous measurement of prompt gamma rays of analyte of interest and current normalizing element. In the present work, an external (in air) PIGE method has been standardized for quantification of low Z elements using nitrogen from atmospheric air as external current normalizer, in which 2313 keV of 14N(p,p’γ)14N is measured. It provides truly nondestructive and greener quantification method for low Z elements by external PIGE. The method was standardized by quantifying total boron mass fractions in ceramic/refractory boron-based samples using low energy proton beam from tandem accelerator. The samples were irradiated with 3.75 MeV proton beam and prompt gamma rays of analyte at 429, 718 and 2125 keV of 10B(p,αγ)7Be, 10B(p,p’γ)10B and 11B(p,p’γ)11B, respectively, and external current normalizers at 136 and 2313 keV were measured simultaneously using high resolution HPGe detector system. The obtained results were compared with external PIGE method using tantalum as external current normalizer, where 136 keV of 181Ta(p,p’γ)181Ta from beam exit window material (Ta) was used for current normalization. The developed method is found to be simple, rapid, convenient, reproducible, truly nondestructive and more economical as no additional beam monitoring instruments are required and it is especially advantageous for direct quantitative analysis of ‘as received’ samples.

Experimental comparison of relative stopping power evaluation between proton CT and x-ray CT for pre-clinical proton irradiation studies of small animals

Objective. Proton therapy experiments in small animals are useful not only for pre-clinical and translational studies, but also for the development of advanced technologies for high-precision proton therapy. While treatment planning for proton therapy is currently based on the stopping power of protons relative to water (i.e. the relative stopping power (RSP)), estimated by converting the CT number into RSP (Hounsfield unit (HU)-RSP conversion) in reconstructed x-ray computed tomography (XCT) images, the HU-RSP conversion causes uncertainties in RSP, which affect the accuracy of dose simulation in patients. Proton computed tomography (pCT) has attracted a great deal of attention due to its potential to reduce RSP uncertainties in clinical treatment planning. However, as the proton energies for irradiating small animals are much lower than those used clinically, the energy dependence of RSP may negatively affect pCT-based RSP evaluation. Here, we explored whether the low-energy pCT approach provided more accurate RSPs when planning proton therapy treatment for small animals. Approach. We evaluated the RSPs of 10 water- and tissue-equivalent materials with known constituent elements based on pCT measurements conducted at 73.6 MeV, then compared them with XCT-based and calculated RSPs to investigate energy dependence and achieve more accurate RSPs for treatment planning in small animals. Main results. Despite the low proton energy, the pCT approach for RSP evaluation yields a smaller root mean square deviation (1.9%) of RSP from the theoretical prediction, compared to conventional HU-RSP conversion with XCT (6.1%). Significance. Low-energy pCT is expected to improve the accuracy of proton therapy treatment planning in pre-clinical studies of small animals if the RSP variation that can be attributed to energy dependence is identical to the variation in the clinical proton energy region.

An investigation of luminescence properties of CaF2: Dy nanophosphor irradiated with gamma rays and low energy proton beams

This paper reports the luminescence properties of nanocrystalline calcium fluoride doped with dysprosium (CaF2: Dy). The nanophosphor has been synthesized by the chemical co-precipitation technique and the dopant concentration has been optimized at 0.3 mol% using thermoluminescence (TL) intensity emitted post 50Gy gamma dose irradiation of samples doped with different dopant concentrations. X-ray diffraction shows the formation of crystalline particles with an average size of 49.233 nm. Photoluminescence (PL) emission spectrum shows the characteristic peaks at 455 nm, 482 nm, 573 nm corresponding to 4I15/2 to 6H15/2, 4F9/2 to 6H15/2 and 4F9/2 to 6H13/2 Dy3+ transitions respectively. PL excitation spectrum shows a peak at 327 nm which corresponds to the Dy3+ transition of 6H15/2 to 4L19/2. Gamma (of 1.25 MeV) and low energy proton beam (of 30 keV) irradiated nanophosphor shows a variation in TL glow curve structure and peak position with an increase in radiation dose/fluence. However, the nanophosphor shows a wide linear dose response for 60Co gamma radiation in the range 10 Gy - 1.5 kGy and for low energy proton beam in the fluence range of 1012–1014 ions/cm2. Srim 2013 has been used to calculate the ion beam parameters including the range of protons in CaF2: Dy 0.3 mol%. The nanophosphor CaF2: Dy could be further investigated as a potential dosimeter for gamma rays and proton beam by studying its TL properties for different energies of these radiations.

Low-energy protons shallow spread-out Bragg peak imaging with a lithium fluoride crystal

The 35 MeV proton beam produced by a modular linear accelerator was used to irradiate at grazing incidence a LiF crystal through a spinning Mylar multi-sector range modulation wheel and a Pyrex range shifter. Starting from a measured pristine depth dose curve, these energy-modulation devices were designed to plan a test shallow spread-out Bragg peak in water. The irradiation of the LiF crystal produced in its lattice a volume distribution of color centers, which could be visualized in a fluorescence microscope as a fluorescent image under blue-light illumination. Since the intensity of this fluorescent image was proportional point-by-point to the absorbed energy, it was elaborated to obtain an experimental depth dose curve in the LiF crystal, from which the proton beam energy distribution was estimated. This latter was finally used to evaluate the corresponding spread-out Bragg peak that would be obtained in water and compare it to the designed one.

General Purpose Transistor Characterized as Dosimetry Sensor of Proton Beams.

A commercial pMOS transistor (MOSFET), 3N163 from Vishay (USA), has been characterized as a low-energy proton beam dosimeter. The top of the samples' housing has been removed to guarantee that protons reached the sensitive area, that is, the silicon die. Irradiations took place at the National Accelerator Centre (Seville, Spain). During irradiations, the transistors were biased to improve the sensitivity, and the silicon temperature was monitored activating the parasitic diode of the MOSFET. Bias voltages of 0, 1, 5, and 10 V were applied to four sets of three transistors, obtaining an averaged sensitivity that was linearly dependent on this voltage. In addition, the short-fading effect was studied, and the uncertainty of this effect was obtained. The bias voltage that provided an acceptable sensitivity, (11.4 ± 0.9) mV/Gy, minimizing the uncertainty due to the fading effect (-0.09 ± 0.11) Gy was 1 V for a total absorbed dose of 40 Gy. Therefore, this off-the-shelf electronic device presents promising characteristics as a dosimeter sensor for proton beams.

The energy dependence of BaSO4: Eu nanophosphors for thermoluminescence dosimetry of orthovoltage X-rays and low energy protons

Accurate dosimetry of ionizing radiation requires careful consideration of the absorption properties of the dosimeter material in question. The energy dependence of a dosimeter signifies the variation in dosimeter signal per absorbed dose to water with radiation type and energy. The nanophosphor BaSO4: Eu is a radiosensitive material for thermoluminescence (TL) dosimetry. However, the energy dependence of the material for orthovoltage X-rays and low energy protons has not previously been investigated, which is the purpose of the current work. We irradiated BaSO4 doped with 0.5 mol% of europium with 100, 160 and 225 kV X-rays and 2 and 9 MeV protons. Co-60 γ-rays were used for reference irradiation. Absolute dose-to-water dosimetry was ensured with an ion chamber. Delivered calibration doses ranged from 0.01 to about 2 Gy. TL output was measured at a heating rate of 5 K/s, where the maximum intensity of the dominant glow peak at about 212 °C defined the dosimeter signal. The signal was found to increase linearly with absorbed dose for both radiation types and all energies. The measured energy response, defined as the ratio of the TL calibration slope at a given radiation type and energy to that following Co-60 γ-irradiation, varied between 47 and 62 for X-rays and between 0.41 and 0.61 for protons. Theoretical modelling of the energy response and proton detector efficiency gave similar trends. The findings show that BaSO4 is an energy-dependent material, especially for X-rays, but may still prove valuable for accurate dose determination if the dosimeter is calibrated in the user beam.

Monte Carlo study of nanoparticles effectiveness on the dose enhancement when irradiated by protons

Recently, the nanomedicine field has experienced considerable growth in research. The use of nanoparticles to enhance dose in radiation treatment was proposed and their potential effects can be indicated using Monte Carlo calculations. The main goal of this study focused on nanoparticles’ (NPs) effects on dose enhancement due to the low-energy protons because the majority of studies on NPs have been conducted for photon radiations. To investigate the effect of NPs on the Dose Enhancement Factor (DEF), a cell dimension phantom was modeled and spheres of NPs were localized inside that. Different NPs, such as Au, Pt, Ag, I, and Ta2O3, were located in the phantom, and the DEF was calculated by changing the source energy from 3 to 15 MeV. The purpose of investigating the low-energy proton beam is to clarify the effects around the Bragg peak in the presence of nanoparticles. For protons with an energy range of 3–15 MeV, it was discovered that Pt nanoparticles have a greater dose increase coefficient of about 1.8 times compared to the other nanoparticles. The findings indicated that the DEF values substantially depended on the NPs concentration, but that the DEF was not significantly affected by changes in concentration or nanoparticle size. Comparative calculations between water and soft tissue phantoms that were filled with NPs presented a difference of less than 2%. The obtained findings emphasized the importance of NPs and considered details, such as concentration, to demonstrate the potential of nanoparticles in improving treatment using protons.