Low-energy Protons Research Articles

Production of radioisotopes for cancer imaging and treatment with compact linear accelerators

Accelerator-produced radioisotopes are widely used in modern medicine, for imaging, for cancer therapy, and for combinations of therapy and diagnostics (theragnostics). Clinical trials are well advanced for several radioisotope-based treatments that might open the way to a strong request of specific accelerator systems dedicated to radioisotope production. While cyclotrons are the standard tool in this domain, we explore here alternative options using linear accelerators. Compared to cyclotrons, linacs have the advantage of modularity, compactness, and reduced beam loss with lower shielding requirements. Although in general more expensive than cyclotrons, linacs are competitive in cost for production of low-energy proton beams, or of intense beams of heavier particles. After a review of radioisotopes of potential interest, in particular produced with low-energy protons or helium, this paper presents two linac-based isotope production systems. The first is a compact RFQ-based system for PET (Positron Emission Tomography) isotopes, and the second is an alpha-particle linac for production of alpha-emitters. The accelerator systems are described, together with calculations of production yields for different targets.

Low-intensity low-temperature analysis of perovskite solar cells for deep space applications

Perovskite solar cells (PSCs) are studied in low-intensity low-temperature (LILT) conditions before and after low energy proton irradiation to characterize device performance at deep space mission-relevant light intensities and temperatures.

Astrophysical S factor and reaction rate of 92,94Mo(p, γ) relevant to the p-process

Abstract. Low energy proton capture cross sections on heavy isotopes are necessary for a better understanding of the astrophysical p-process. There are around 35 proton-rich stable isotopes between 74S e and 196Hg which are bypassed by the s- and r- processes. These are commonly referred as p-nuclei whose origin is still not completely understood. In the present study, proton capture reactions are studied on Mo isotopes at astrophysically relevant energies using nuclear modular code TALYS. Astrophysical S factor and reaction rates are also calculated inside a core-collapse supernova. The obtained results are compared with the literature data taken from EXFOR data library. In addition, the effect of different combinations of the nuclear input parameters entering the stellar reaction rate have been investigated.

Novel Ultraviolet and Ionizing Radiation Detectors Made From TiO Wide-Bandgap Semiconductor

We describe the fabrication and characterization of a novel ultraviolet (UV) and ionizing radiation detector using a polycrystalline TiO2 wide-bandgap semiconductor as the active material. The detector geometry we have developed and tested is a polycrystalline TiO2 thin film with planar electrode contacts for signal pickup. Several prototypes were fabricated using two single-step techniques. We present the dc characterization of these devices and the signal response to the UV light and low-energy proton beam irradiation. The detector prototypes show excellent dc characteristics and fast ac signal response at bias voltage as low as 50 V.

Jet Cloud–Star Interaction as an Interpretation of Neutrino Outburst from the Blazar TXS 0506+056

A neutrino outburst between September 2014 and March 2015 was discovered from the blazar TXS 0506+056 by an investigation of 9.5 years of IceCube data, while the blazar was in a quiescent state during the outburst with a gamma-ray flux of only about one-fifth of the neutrino flux. In this work, we give a possible interpretation of the abnormal feature by proposing that the neutrino outburst originated from the interaction between a relativistic jet and a dense gas cloud formed via the tidally disrupted envelope of a red giant being blown apart by the impact of the jet. Gamma-ray photons and electron/positron pairs produced through the hadronuclear interactions, correspondingly, will induce electromagnetic cascades and then make the cloud ionized and thermalized. The EM radiation from jet cloud–star interaction is mainly contributed by the relatively low-energy relativistic protons which propagate in the diffusion regime inside the cloud due to magnetic deflections, whereas the observed high-energy neutrinos (≳100 TeV) are produced by the relatively high-energy protons which can continue to beam owing to the weak magnetic deflections, inducing a much higher flux of neutrinos than electromagnetic radiation. The observed low-energy electromagnetic radiations during the neutrino outburst period are almost the same as that in the quiescent state of the source, so it may arise mainly as the same state as the generally quiescent. As a result, due to the intrusion of a dense cloud, the neutrino outburst can be expected, and, in the meantime, the accompanying electromagnetic radiations from hadronic processes will not cause any enhancement in the blazar’s electromagnetic flux.

BRAND—A detection system for [formula omitted]-decay correlation measurement

The BRAND experiment aims at the search of Beyond Standard Model (BSM) physics via measurement of exotic components of the weak interaction. For this purpose, eleven correlation coefficients of neutron β-decay will be measured simultaneously. The BRAND detection system is oriented for the registration of charged products of β-decay of polarized, free neutrons. With the measurement of the four-momenta of electron and proton, the complete kinematic of the decay will be determined. Moreover, the transverse spin component of the electron, which is the crucial observable to probe BSM exotic components of weak interaction, will be measured via Mott scattering. The electron detection system features both tracking and energy measurement capability. It is also responsible for the determination of the electron spin orientation. A challenging detection of low-energy protons from the β-decay is performed with a system, which involves the acceleration and subsequent conversion of protons into bunches of electrons. To test the feasibility of the proposed experimental techniques, a small-scale prototype setup was installed at the cold neutron beam facility PF1B at the Laue-Langevin Institute (ILL) in Grenoble, France. In this contribution, the preliminary results of the commissioning run are presented with an emphasis on the performance of individual parts of the detection system.

Absolute dose measurement and energy dependence of LiF dosimeters in proton therapy beam dosimetry

Background: For the purpose of patient dose monitoring, thermoluminescent dosimeters (TLDs) can report any dose point of interest as in vivo dosimetry. However, energy dependence of TLDs may perturb proton beam dosimetry, particularly for low-energy proton beams. The purpose of this study was to evaluate the energy dependence of TLDs for proton beams and influence on dosimetry.

Relation between magnetosonic waves and pitch angle anisotropy of warm protons

In the past decade, many observations of transversely heated low energy protons were reported in the inner magnetosphere. Interestingly, most of the time heated protons were observed along with magnetosonic waves. Due to the strong correlation, it was often assumed that magnetosonic waves were responsible for the heating of low energy protons. By performing a case study under unusually disturbed geomagnetic conditions, this paper unravels the controversial relationship between the observed pitch angle anisotropy of warm protons and the accompanying magnetosonic waves in the inner magnetosphere. We perform a comparative analysis involving two nearly identical cases of pitch angle anisotropy of warm protons in low L-shell region–one with magnetosonic waves and one without them. It is found that magnetosonic waves are not responsible for primary heating of low-energy protons and may just marginally alter the shape of the distribution of heated protons in the events analyzed. Based on the recent Cluster and POLAR observations, we also show how the recirculated polar wind plasma in the Earth’s magnetosphere can cause the concurrent appearance of heated protons and magnetosonic waves.

Characterisation of a scintillating fibre-based hodoscope exposed to the CNAO low-energy proton beam

A 32 × 32 Bicron 1 mm2 polystyrene scintillating fibre-based beam hodoscope, with an entrance window of 6.3 × 6.3 cm2, has been designed and characterised for monitoring low-energy charged particle beams. The hodoscope, designed to fit into the 60 MeV/c negative muon beam at the RIKEN-RAL muon facility (UK) for the FAMU experiment, will enable muon counting for data normalisation. We describe a calibration technique to enable the detector to work as a muon stream counter by knowing the muon equivalent charge deposited in the detector. This value is obtained by exposing the detector to a single-proton beam at the CNAO hadron therapy synchrotron, with the energy set to have the same energy loss profile as 60 MeV/c negative muons.

ИМПУЛЬСНЫЕ ХАРАКТЕРИСТИКИ КРЕМНИЕВЫХ СТРУКТУР С N-P ПЕРЕХОДОМ, ОБЛУЧЕННЫХ ПРОТОНАМИ

Currently, methods are being actively developed to create semiconductor structures with desiredproperties by irradiation with ionizing particles (radiation defect engineering). The interactionof radiation defects with impurities, dislocations and other structural defects causes a change in theproperties of semiconductors and semiconductor devices. Irradiation with protons makes it possibleto controllably create radiation defects with a distribution maximum in a pre-calculated region. Theaim of this work is to analyze the effect of irradiation with low-energy protons on the impulse characteristicsof silicon structures with an n+-p junction. The task is to determine the effective lifetime  ofcharge carriers in the space charge region (SCR) of the n+-p junction. The n+-p-p+-structures madeof silicon grown by the Czochralski method, irradiated from the side of the n+-layer by a low-energyproton flux at sample temperatures of 300 K and 83 K were studied. To measure the impulse characteristics,bipolar rectangular voltage pulses with a constant amplitude of 10 mV and a frequency of1 MHz were used. The experimental data are explained using models of nonstationary charge carriertransport in inhomogeneous semiconductors and the formation of radiation defects in silicon underthe action of protons. Depth distributions of the average number of primary radiation defects arecalculated: interstitial silicon, vacancies, divacancies created by one proton per unit length of theprojective path. It is shown that irradiation with protons with a dose of 1015 cm2 and an energy of40 keV does not change the value of , but with an energy of 180 keV creates a region with an effectivelifetime of 5.5108 s in the SCR of the n+-p junction.

Optical fibre array detector to monitor irradiations for medical radioisotope production

Low-energy cyclotrons are in use worldwide to produce medical radioisotopes for nuclear medicine. Beam monitoring during the irradiation of targets is difficult due to the high-power density of low-energy protons, space limitations, and interference with beam delivery. Doped silica fibres are sensitive to prompt ionizing radiation from the bombarded target, and produce radiation induced luminescence (RIL) when exposed. The fibres can be attached to the outside of the target in a low-profile fibre array, ensuring efficient and safe operation. Here, we present the results from our prototype of such a fibre array. It consists of four Ce-doped fibres with a diameter of 200 μm and has been installed at the TR13 medical cyclotron at TRIUMF where it has been tested at different irradiation conditions.

Demonstrative measurement of proton-nuclear reaction by deconvolving the prompt gamma-ray spectra

In proton therapy, there has been an increasing demand for measuring the employed dose distribution to improve treatment accuracy and quality. One method of estimating radiation dose in real time is to visualize the prompt gamma rays emitted during nuclear reactions between protons and nuclei in the patient’s body. However, this is difficult without accurate measurements of nuclear cross sections, that cover a 10–100 MeV energy range. Herein, we propose a novel method for determining cross section of low-energy protons with 12C and 16O by measuring the prompt gamma rays emitted from stacked slab phantoms placed along the proton path. These emitted gamma rays provide direct information on the nuclear reactions occurring at different proton energies. By applying an iterative inference using the response matrix, the contamination of various prompt gamma rays can be resolved; thus, the cross sections of various reactions were obtained at arbitrary proton energies. As a first step to this study, we applied this method to measure the nuclear reaction of protons with 12C and 16O nuclei, which are the major elements constituting the human body. The cross section of the 12C(p,p)12C∗ reaction, which produces a prominent gamma-ray peak at 4.4 MeV, reproduced the one in literature well, supporting the validity of the proposed method. Furthermore, we show that even weak prompt gamma rays can be resolved for a wide range of proton energies below 70 MeV, for which no cross sectional data have been reported so far.

Commissioning and validation of a novel commercial TPS for ocular proton therapy.

Until today, the majority of ocular proton treatments worldwide were planned with the EYEPLAN treatment planning system (TPS). Recently, the commercial, computed tomography (CT)-based TPS for ocular proton therapy RayOcular was released, which follows the general concepts of model-based treatment planning approach in conjunction with a pencil-beam-type dose algorithm (PBA). To validate RayOcular with respect to two main features: accurate geometrical representation of the eye model and accuracy of its dose calculation algorithm in combination with an Ion Beam Applications (IBA) eye treatment delivery system. Different 3D-printed eye-ball-phantoms were fabricated to test the geometrical representation of the corresponding CT-based model, both in orthogonal 2D images for X-ray image overlay and in fundus view overlaid with a funduscopy. For the latter, the phantom was equipped with a lens matching refraction of the human eye. Funduscopy was acquired in a Zeiss Claus 500 camera. Tantalum clips and fiducials attached to the phantoms were localized in the TPS model, and residual deviations to the actual position in X-ray images for various orientations of the phantom were determined, after the nominal eye orientation was corrected in RayOcular to obtain a best overall fit. In the fundus view, deviations between known and displayed distances were measured. Dose calculation accuracy of the PBA on a 0.2mm grid was investigated by comparing between measured lateral and depth-dose profiles in water for various combinations of range, modulation, and field-size. Ultimately, the modeling of dose distributions behind wedges was tested. A 1D gamma-test was applied, and the lateral and distal penumbra were further compared. Average residuals between model clips and visible clips/fiducials in orthogonal X-ray images were within 0.3mm, including different orientations of the phantom. The differences between measured distances on the registered funduscopy image in the RayOcular fundus view and the known ground-truth were within 1mm up to 10.5mm distance from the posterior pole. No clear benefit projection of either polar mode or camera mode could be identified, the latter mimicking camera properties. Measured dose distributions were reproduced with gamma-test pass-rates of >95% with 2%/0.3mm for depth and lateral profiles in the middle of spread-out Bragg-peaks. Distal falloff and lateral penumbra were within 0.2mm for fields without a wedge. For shallow depths, the agreement was worse, reaching pass-rates down to 80% with 5%/0.3mm when comparing lateral profiles in air. This is caused by low-energy protons from a scatter source in the IBA system not modeled by RayOcular. Dose distributions modified by wedges were reproduced, matching the wedge-induced broadening of the lateral penumbra to within 0.4mm for the investigated cases and showing the excess dose within the field due to wedge scatter. RayOcular was validated for its use with an IBA single scattering delivery nozzle. Geometric modeling of the eye and representation of 2D projections fulfill clinical requirements. The PBA dose calculation reproduces measured distributions and allows explicit handling of wedges, overcoming approximations of simpler dose calculation algorithms used in other systems.

FLASH vs. Conventional Dose Rate Proton Radiation in Mouse Abdomen

<h3>Purpose/Objective(s)</h3> The mechanisms underlying normal tissue toxicity sparing and survival benefits of ultra-high dose rate radiation (FLASH) are still unclear. We used a low-energy proton system (50 MeV) optimized for small animal radiobiological research to study the biological effects after FLASH and conventional dose rate (CONV) proton radiation to mouse abdomen. <h3>Materials/Methods</h3> We radiated the abdomen of 6–7-week-old female C57BL/6 mice using the plateau region of a continuous (unpulsed) cyclotron-generated 50 MeV preclinical proton beam, transmitting through the abdomen, with 1.5cm (for survival study) or 3cm (for EdU assay) width of beam via customized vertical and horizontal collimators. Mice survival and regenerated crypts in colon tissues using EdU assay were studied. Mice were stratified into 3 groups: 1) control/sham radiation (n=8 for survival, n=4 for EdU); 2) FLASH (20Gy at 48-93Gy/sec, n=22 for survival and n=13 for EdU); 3) CONV (20Gy at ∼1Gy/sec, n=19 for survival, n=11 for EdU). For survival study, mice were observed for survival post radiation. For EdU assay, the mice were injected with EdU 3-4 hours prior to euthanasia, and colon tissues were collected at 24 hours and 96 hours post-radiation for sectioning and then EdU staining. <h3>Results</h3> FLASH and CONV groups showed different survival: FLASH (13 days post radiation, 36.4% survival); CONV (15.6% survival, P = 0.04). FLASH group had more EdU staining than the CONV group, though both FLASH and CONV groups showed reduced EdU staining compared to the control group. <h3>Conclusion</h3> Preliminary results of mouse abdomen FLASH and CONV proton radiation from a 50 MeV beam suggest FLASH proton radiation leads to better survival and less normal tissue damage than CONV radiation.

Low energy protons as probes of hadronization dynamics

Energetic quarks liberated from hadrons in nuclear deep-inelastic scattering propagate through the nuclear medium, interacting with it via several processes. These include quark energy loss and nuclear interactions of forming hadrons. One manifestation of these interactions is the enhanced emission of low-energy charged particles, referred to as grey tracks. We use the theoretical components of the BeAGLE event generator to interpret grey track signatures of parton transport and hadron formation by comparing its predictions to E665 data. We extend the base version of BeAGLE by adding four different options for describing parton energy loss. The E665 data we used consists of multiplicity ratios for fixed-target scattering of 490 GeV muons on Xe normalized to deuterium as a function of the number of grey tracks. We compare multiplicity ratios for E665 grey tracks to the predictions of BeAGLE, varying the options and parameters to determine which physics phenomena can be identified by these data. We find that grey tracks are unaffected by modifications of the forward production. Thus their production must be dominated by interactions with hadrons in the backward region. This offers the advantage that selecting certain particles in the forward region is unlikely to bias a centrality selection. We see a strong correlation between the number of grey tracks and the in-medium path length. Our energy loss model does not reproduce the suppression observed in the projectile region. We see an underprediction of the proton production rate in backward kinematics, suggesting that a stronger source of interaction with the nuclear medium is needed for accurate modeling. These results lay an important foundation for future spectator tagging studies at both Jefferson Lab and at the Electron-Ion Collider, where neutron and proton grey track studies will be feasible down to very small momenta.

Measurement of X-ray production cross sections for lower-energy (0.7-3 MeV) proton induced Cu_K, Ag_L and Au_M X-rays from thick samples

We conducted a series of fundamental research-based experimentations to measure the X-ray production cross sections of K-, L-, and M-shells from thick samples of Cu, Ag and Au, respectively, for proton beam in a lower energy range of 0.7 - 3.5 MeV utilizing particle induced X-ray emission (PIXE) analysis. The measurement theories based on the Merzbacher-Lewis (ML) relationship and procedure for thick samples are described. The detector efficiency and system calibration were first measured from Fe-55 and Am-241 X-ray sources and the standard sample, respectively. The X-ray yields as a function of the proton energy were measured and fitted for finding the derivatives which were used for the cross section measurement. The obtained results were compared with published data and predictions from the theoretical models of Plane Wave Born Approximation (PWBA) and the advanced ECPSSR. The measured results from Cu were in good agreement with the theoretical predictions, especially in the lower energy regime, and most of the reported data, while for the higher energy regime deviated by a few times but still in the same order of magnitude with the theoretical data. The Ag and Au results were in excellent agreement with published and theoretical values.

A unified model for TCAD simulation of the charge generated in semiconductors by low-energy alpha particles and protons

TCAD simulation of the generation and transport of ionization tracks produced in semiconductors by ions is very relevant for device reliability, as well for the design of radiation detectors. This paper presents a unified model calibrated and validated for the charge generated along the ionization track of low-energy alpha particles and protons in Si, SiC, Ge, GaAs, and GaN. The new model presents several advantages over the traditional ones, in particular the ease of calibration, the numerical stability, and capability to be extended to other ion types.

Molecular level manipulation of charge density for solid-liquid TENG system by proton irradiation

With the rapid development of flexible electronics, methods for improving the performance of self-powered triboelectric nanogenerators (TENGs) have been in continuous demand. Due to its low density, and excellent physical and chemical properties, polyimide (Kapton or PI) was applied widely in space. As space materials such as spacecraft, PI will be irradiated by protons and other charged particles during the long-term service in space. In this study, we proposed a surface modification method using low-energy proton irradiation for tuning the internal chemical structure and functional groups at the molecular level and improving TENG performance. A solid-liquid dual-phase TENG using gallium–indium (Ga-In) eutectic alloy as liquid-phase friction material and PI as solid-phase friction material was successfully prepared. Systematic studies about the PI performance induced by proton irradiation parameters can bring insights into the interaction between the density of unsaturated bonds and electrification performance. The effect mechanism of proton irradiation on TENG property was elucidated. Compared with the initial state, the open-circuit voltage of the solid-liquid dual-phase TENG based on Ga-In eutectic alloy increased by about 57.4 % to 107.5 V, the short-circuit current density was 2.02 μA·cm−2, and the charge transfer density was 103.22 μC·m−2. Astonishingly, proton irradiation, which normally has adverse effects on devices, achieved a significant improvement in solid-liquid dual-phase TENG performance. High charge density is the key factor affecting the performance of TENG devices, and this study revealed a different approach for modifying the characteristics of solid-liquid dual-phase TENG. On the basis of the results of this study and through a series of possible breakthroughs in outer space and other environments, the reliable power supply by Ga-In eutectic alloy integrated TENG, under the presence of radiation, can be realized.

Cross-section measurement for an optimized 61Cu production at an 18 MeV medical cyclotron from natural Zn and enriched 64Zn solid targets

The availability of novel medical radionuclides is a key point in the development of personalised nuclear medicine. In particular, copper radioisotopes are attracting considerable interest as they can be used to label various molecules of medical interest, such as proteins and peptides, and offer two of the most promising true theranostic pairs, namely 61Cu/67Cu and 64Cu/67Cu. Although 64Cu (t1/2 = 12.7006 h, β+: 17.6%, β−: 38.5%) is nowadays the most commonly used as a diagnostic radionuclide, 61Cu (t1/2 = 3.339 h, β+: 61%) features more favourable nuclear properties, such as a higher positron decay fraction and the absence of β− emissions. To date, the production of 61Cu has been carried out irradiating highly enriched 61Ni targets with a low energy proton beam. However, the use of the very expensive 61Ni targets requires an efficient recovery of the target material and makes this method quite inconvenient. Another promising production route is the proton irradiation of natural Zn or enriched 64Zn targets, exploiting the (p,α) nuclear reaction. Along this line, a research program is ongoing at the Bern medical cyclotron, equipped with an external beam transfer line and a solid target station. In this paper, we report on cross-section measurements of the 64Zn(p,α)61Cu nuclear reaction using natural Zn and enriched 64Zn material, which served as the basis to perform optimized 61Cu production tests with solid targets.

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.