High-energy Proton Beam Research Articles

Volume reflection of high-energy protons in short bent crystals

Characteristics of volume reflection for high-energy protons in short bent crystals are considered by simulation. The deflection efficiency and angle depend on the bend radius of the crystal. The concurrent process of volume capture of particles into channeling states limits the reflection efficiency. The optimal parameters of a crystal for using it as a beam reflector were determined.It was shown that the deflection efficiency of high-energy proton beams by the sequence of reflections in short bent crystals is high for small deflection angles. This allows considering possible applications of crystal reflectors for the beam collimation of hadrons colliders and for high-energy physics experiments.

A telescope for monitoring fast neutron sources

In the framework of nuclear waste management, highly radiotoxic long-lived fission products and minor actinides are planned to be transmuted in a sub-critical reactor coupled with an intense external neutron source. The latter source would be created by a high-energy proton beam hitting a high atomic number target. Such a new system, termed an accelerator-driven system (ADS), requires on-line and robust reactivity monitoring. The ratio between the beam current delivered by the accelerator and the reactor power level, or core neutron flux, is the basis of one method which could give access to a core reactivity change. In order to test reactivity measurement technique, some experimental programs use 14-MeV neutrons originating from the interaction of a deuteron beam with a tritium target as an external neutron source. In this case, the target tritium consumption over time precludes use of the beam current for reactivity monitoring and the external neutron source intensity must be monitored directly. A range telescope has been developed for this purpose, consisting of the assembly of a hydrogenous neutron converter and three silicon stages where the recoiling protons are detected. In this article, the performances of such a telescope are presented and compared to Monte-Carlo simulations.

Fabrication and characterization of microcavity lasers in rhodamine B doped SU8 using high energy proton beam

The authors present their results on the characterization of individual dye-doped microcavity polymer lasers fabricated using a high energy proton beam. The lasers were fabricated in rhodamine B doped SU8 resist with a single exposure step followed by chemical processing. The resulting trapezoidal shaped cavities had dimensions of ∼250×250μm2. Physical characterization of these structures was performed using a scanning electron microscope while the optical characterization was carried out by recording the emission subsequent to pumping the lasers with 532nm, 6 nanosecond pulses. The authors observed intense, narrow emission near 624nm with the best emission linewidth full width at half maximum of ∼9nm and a threshold ∼150μJ∕mm2.

Laser ablation of ion irradiated CR-39

The effects of multiple pulses of a CO2 laser with energy of 2.5 J and pulse duration of 200 ns on the surface morphology of ion irradiated CR-39 is investigated in light of the modification in its track registration properties. For this purpose, a CR-39 was exposed by a CO2 laser generated hydrogen, argon, cadmium, air molecular ions (N2 and O2, etc.), high energy (300 KeV) proton beam from Cock Croft Walton accelerator, and α (5 MeV) from 0.5 μCi Pu239 source. The registered tracks were enlarged after 6 h of 6.25 N NaOH etching. These etched detectors were then exposed to different number of CO2 laser shots. The etched detectors were then analyzed by a computer controlled optical microscope (Lexica DMR series). It was observed that even a single shot of CO2 laser, irrespective of the registered ions tracks, can change the track registration properties of CR-39, and can remove the vaporization resistant skin present on the polymer (CR-39). A significant change in track density and track shaping regardless of the ions is observed. At the outside of the focal area, the ion density of different registered tracks is compared graphically before and after laser irradiation. Laser ablation of unexposed CR-39 is also done with multiple pulses CO2 laser. In this regard, the coherent and non-coherent structures, diffraction patterns, circular fringes with corrugations and ripples, droplets, chain like structures with cluster formation, chain folded crystallites, and hole drilling were observed. The irradiation induced ablation of the polymer is of great importance in electronics industry, lithography, etc.

The Italian project for a proton imaging device

Proton Computed Tomography (or pCT) is a new imaging technique based on the use of high energy proton beams (200–250 MeV) replacing of the commonly adopted X-rays CT. pCT that was firstly proposed in the 1960s but only nowadays, with the continued establishing of new proton therapy centers around the world, the interest in it is growing. The use of protons for tomographic images can represent, in fact, a big enhancement in the quality of a proton therapy treatment either in the patient positioning as well as in the accuracy of the dose calculation for the treatment planning phase. In this paper, after a brief introduction on pCT principles, the main hardware and software characteristics of a first pCT prototype in development by our group (the Italian PRIMA collaboration) will be presented. The role of Monte Carlo simulation in developing will be also emphasized, using the GEANT4 simulation toolkit.

Thermal hydraulic studies of spallation target for one-way coupled indian accelerator driven systems with low energy proton beam

BARC has recently proposed a one-way coupled ADS reactor. This reactor requires typically ∼1 GeV proton beam with 2 mA of current. Approximately 8 kW of heat is deposited in the window of the target. Circulating liquid metal target (lead/lead-bismuth-eutectic) has to extract this heat and this is a critical R&D problem to be solved. At present there are very few accelerators, which can give few mA and high-energy proton beam. However, accelerators with low energy and hundreds of micro-ampere current are commercially available. In view of this, it is proposed in this paper to simulate beam window heating of ∼8 kW in the target with low-energy proton beam. Detailed thermal analysis in the spallation and window region has been carried out to study the capability of heat extraction by circulating LBE for a typical target loop with a proton beam of 30 MeV energy and current of 0.267 mA. The heat deposition study is carried out using FLUKA code and flow analysis by CFD code. The detailed analysis of this work is presented in this paper.

Measurement of the Electron Density Produced by the Prepulse in an Experiment of High Energy Proton Beam Generation

The characteristics of the preplasma, such as the electron density and its profile, were investigated from a measurement of the phase shift due to the preplasma in an experiment on high energy proton beam generation. The electron density and its profile were calculated from the measured phase shifts, and their dependences on the prepulse intensity and the time delay were investigated. Although the size of the electron density depended on the prepulse intensity, the maximum electron density ranged from 1.5 ◊ 10 19 to 2.1 ◊ 10 19 cm 3 , irrespective of the prepulse intensity and the time delay in the picosecond range. The analysis showed that a preplasma having an electron density of 10 19 cm 3 existed on a target before the main laser pulse arrived at the target for the

J-PARC中性子源用低温水素システムの安全設計

The Japan Atomic Energy Agency has been constructing the Japan Proton Accelerator Research Complex (J-PARC), a high intensity proton accelerator complex with MW beam power, in collaboration with the High-Energy Accelerator Research Organization. The materials and life science experimental facility (MLF), where materials and biological structures are analyzed using neutron beam-scattering experiment, has been constructed as one of the experimental science facilities at J-PARC. A spallation neutron source that produces neutrons through nuclear spallation reaction using high-energy proton beam injection and provides neutron beams for experimental users has been installed at the MLF. Hydrogen nuclei are used as a neutron moderating material (moderator) to reduce the neutron energy from MeV to meV order. Therefore, a cryogenic hydrogen system should be installed at the spallation neutron source to provide supercritical hydrogen to moderators. This paper describes the safety design of the cryogenic hydrogen system. Especially, the system is subject to high-pressure gas safety laws, and refrigeration safety regulations are applied to the system for the first time. We also discuss the technical contents that were argued through this application.

Depth absorbed dose and LET distributions of therapeutic , , , and beams

The depth absorbed dose and LET (linear energy transfer) distribution of different ions of clinical interest such as , , , and ions have been investigated using the Monte Carlo code SHIELD‐HIT. The energies of the projectiles correspond to ranges in water and soft tissue of approximately . The depth dose distributions of the primary particles and their secondaries have been calculated and separated with regard to their low and high LET components. A LET value below can generally be regarded as low LET and sparsely ionizing like electrons and photons. The high LET region may be assumed to start at where on average two double‐strand breaks can be formed when crossing the periphery of a nucleosome, even though strictly speaking the LET limits are not sharp and ought to vary with the charge and mass of the ion. At the Bragg peak of a monoenergetic high energy proton beam, less than 3% of the total absorbed dose is comprised of high LET components above . The high LET contribution to the total absorbed dose in the Bragg peak is significantly larger with increasing ion charge as a natural result of higher stopping power and lower range straggling. The fact that the range straggling and multiple scattering are reduced by half from hydrogen to helium increases the possibility to accurately deposit only the high LET component in the tumor with negligible dose to organs at risk. Therefore, the lateral penumbra is significantly improved and the higher dose gradients of and ions both longitudinally and laterally will be of major advantage in biological optimized radiation therapy. With increasing charge of the ion, the high LET absorbed dose in the beam entrance and the plateau regions where healthy normal tissues are generally located is also increased. The dose distribution of the high LET components in the beam is only located around the Bragg peak, characterized by a Gaussian‐type distribution. Furthermore, the secondary particles produced by high energy ions in tissuelike media have mainly low LET character both in front of and beyond the Bragg peak.

Radiation hardness of the electrical properties of carbon nanotube network field effecttransistors under high-energy proton irradiation

The effect of high-energy proton irradiation on the physical properties of carbon nanotubes(CNTs) was investigated. The focus of the study was on the electrical properties ofsingle-walled carbon nanotube (SWNT) network devices exposed to proton beams.Field-effect transistors (FETs) of network type were fabricated using SWNTs andwere then irradiated by high-energy proton beams of 10–35 MeV with a fluence of4 × 1010–4 × 1012 cm−2 that are comparable to the aerospace radiation environment. The electrical properties ofboth metallic and semiconducting CNT network FET devices underwent no significantchange after the high-energy proton irradiation, indicating that the CNT network devicesare very tolerant in proton beams. Raman spectra confirm the proton-radiation hardness ofCNT network FET devices. The radiation hardness of CNT network FET devices promisestherefore the potential usefulness of CNT-based electronics for future space application.

A dc arc plasma torch as a tailored heat source for thermohydraulic simulation of proton beam–target interaction in ADSS

Currently, research on accelerator driven subcritical systems (ADSS) is gaining significance due to their high safety levels and extremely attractive potential in terms of both thorium utilization and nuclear waste transmutation. While high energy and high current proton beams are being built worldwide, intensive efforts are being undertaken in parallel towards the development of complex lead bismuth eutectic target systems. The major focus is directed towards understanding of the material compatibility and detailed thermohydraulic simulation of the liquid metal flow. The requisite heat flux is being deposited using innovative and easily controllable heat sources. This paper presents an experimental and simulation study to explore the potential of using dc arc plasma torches as a tailored heat source for thermohydraulic simulation of proton beam–target interaction in such systems.

PRELIMINARY RESULTS ON HYDROPHONES CALIBRATION WITH PROTON BEAM

Huge sensitive volumes will be required to identify interactions of U.H.E. cosmic neutrinos with energy above 1016eV. New detectors and new techniques have to be developed to open this future field of H.E. astrophysics. We report on the study of acoustic signals induced by the interaction in water of a high intensity low energy proton beam (ITEP, Moscow). Acoustic signals have been collected by means of high sensitivity deep-sea hydrophones, for proton energy deposition close to 0.1 Joule. Hydrophones sensitivity has been previously characterized at the acoustic test facilities of IDAC-CNR (Rome). Results show a good linearity between the proton beam intensity and the hydrophones signal amplitude. Results are encouraging for the future detection of highenergy neutrino-induced showers developing in deep-sea water.

Tensile testing of EP-823 and HT-9 after irradiation in STIP II

The predicted operating conditions for a lead–bismuth eutectic target to be used in an accelerator driven system for the Advanced Fuel Cycle Initiative spans a temperature range of 300–600 °C while being irradiated by a high energy (∼600 MeV) proton beam. Such spallation conditions lead to high displacement rates coupled with high accumulation rates of helium and hydrogen up to 150 appm/dpa. Two candidate ferritic/martensitic materials for these applications include HT-9 and EP-823. To investigate the effect of irradiation on these materials, the tensile properties were measured at 25, 250, and 400 °C after irradiation in the STIP II irradiation to doses up to 20 dpa at temperatures up to 350 °C. Losses in ductility concomitant with increases in yield stress are observed in both alloys although the embrittlement is more severe in the EP-823. This stronger embrittlement is attributed to the high silicon content in EP-823.

Thermal hydraulics of the spallation target module of an accelerator driven sub-critical system: A numerical study

The mechanical design of the target module of an accelerator driven sub-critical nuclear reactor system (ADSS) calls for an analysis of the related thermal–hydraulic issues because of the sheer large amount of heat generation in its spallation target system during the course of nuclear interactions with the molten lead bismuth eutectic (LBE) target. The window of the target module is subject to high heat fluxes due to the direct impingement of high energy proton beam on its surface. A large amount of heat is deposited on the window and in the bulk of the LBE in the spallation region. Therefore, the problem of heat removal by the LBE is a challenging thermal–hydraulic issue. For this, one will need to examine the laminar/turbulent flows of low Prandtl number fluids (LBE) in a complex target module of an ADSS. In this study, the equations governing the flow and thermal energy are solved numerically using the streamline upwind Petrov–Galerkin (SUPG) finite element (FE) method. Special consideration has been given to the window under various thermal conditions, such as, isothermal, uniform and variable heat flux. The analysis has been extended to the case of heat generation in the liquid LBE. The principal purpose of the analysis is to trace the temperature distribution on the beam window and in the LBE. This also helps to check the suitability of the geometry in avoiding the recirculation or stagnation zones in the flow space that may lead to hot spots.

Hydrogen microscopy and analysis of DNA repair using focused high energy ion beams

The ion microprobe SNAKE (Supraleitendes Nanoskop für Angewandte Kernphysikalische Experimente) at the Munich 14MV tandem accelerator achieves beam focussing by a superconducting quadrupole doublet and can make use of a broad range of ions and ion energies, i.e. 4–28MeV protons or up to 250MeV gold ions. Due to these ion beams, SNAKE is particularly attractive for ion beam analyses in various fields. Here we describe two main applications of SNAKE. One is the unique possibility to perform three-dimensional hydrogen microscopy by elastic proton–proton scattering utilizing high energy proton beams. The high proton energies allow the analysis of samples with a thickness in the 100μm range with micrometer resolution and a sensitivity better than 1ppm. In a second application, SNAKE is used to analyse protein dynamics in cells by irradiating live cells with single focussed ions. Fluorescence from immunostained protein 53BP1 is used as biological track detector after irradiation of HeLa cells. It is used to examine the irradiated region in comparison with the targeted region. Observed patterns of fluorescence foci agree reasonably well with irradiation patterns, indicating an overall targeting accuracy of about 2μm while the beam spot size is less than 0.5μm in diameter. This performance shows successful adaptation of SNAKE for biological experiments where cells are targeted on a sub-cellular level by energetic ions.

Fabrication of buried channel waveguides in photosensitive glass using proton beam writing

We report our results on the fabrication and characterization of buried, channel optical waveguides in photosensitive Foturan™ glass using a high energy proton beam. Waveguides were fabricated with varying fluence, and the propagation loss and refractive index change were measured. Near-field mode data measured at 632.8nm showed that waveguiding could be achieved for all fluences ranging from 1014to1016protons∕cm2. The maximum positive refractive index change of 1.6×10−3 was measured for the highest fluence. The waveguide propagation losses measured using the scattering technique were estimated to be in the range of 8.3–12.9dB∕cm, increasing with proton fluence.

Radiation hardness of amorphous silicon particle sensors

Radiation tests of 32μm thick hydrogenated amorphous silicon n–i–p diodes have been performed using a high-energy 24GeV proton beam up to fluences of 2×1016protons/cm2. The results are compared to irradiation of similar 1μm and 32μm thick n–i–p diodes using a proton beam of 405keV at a fluence of 3×1013protons/cm2. All samples exhibited a drop of the photoconductivity and an increase in the dark leakage current under both high- and low-energy proton irradiation. An almost full recovery of the device performance was observed after a subsequent thermal annealing.

Design of a high energy proton beam dump for KOMAC

The proton energy and the average current of the Korea Multipurpose Accelerator Complex(KOMAC) should be 20 MeV and 4.8 mA, respectively. This creates a beam power of 96 kW. By considering a FWHM of 1 cm with a Gaussian distribution, the average power density is 139 kW/cm 3 with a peak power of 200 kW/cm 3 . In this paper, a design concept for the KOMAC beam dump to safely absorb the proton beam energy will be presented and the numerical results of the heat transfer and the thermal stress analyses will be discussed.

Going up?

Treating cancer with beams of high-energy protons is just one of the exciting possibilities presented by the advent of laser-based particle accelerators. But how soon will these devices reach the performance levels needed for such applications, and how will these improvements be made?

Laser-driven proton scaling laws and new paths towards energy increase

The past few years have seen remarkable progress in the development of laser-based particle accelerators. The ability to produce ultrabright beams of multi-megaelectronvolt protons routinely has many potential uses from engineering to medicine, but for this potential to be realized substantial improvements in the performances of these devices must be made. Here we show that in the laser-driven accelerator that has been demonstrated experimentally to produce the highest energy protons, scaling laws derived from fluid models and supported by numerical simulations can be used to accurately describe the acceleration of proton beams for a large range of laser and target parameters. This enables us to evaluate the laser parameters needed to produce high-energy and high-quality proton beams of interest for radiography of dense objects or proton therapy of deep-seated tumours.