Incident Carbon Ions Research Articles

Microstructure and tribological behavior in ta-C films prepared by laser-induced filtered cathodic vacuum arc technique: Effect of charge voltage

As an important power supply parameter, charge voltage has a significant influence on the properties of deposited films. In this work, the ta-C films were fabricated by the laser-induced filtered cathodic vacuum arc technique (LI-FCVA). The effect of charge voltage on microstructure, mechanical and tribological properties of ta-C films was investigated. Although macro-particles with various sizes were clearly visible on surfaces of films, the surface roughness was declined with increase of charge voltage. The sp3-C bond ratio in films was closely dependent on the charge voltage. At 160 V charge voltage, the sp3-C bond ratio was 54.1 %, then reaching to 61.2 % at the charge voltage of 190 V. With further increasing to 250 V, the sp3-C ratio slowly down to 57.1 %. This is ascribed to the change in energy for incident carbon ions which governed by the charge voltage. The highest hardness value, 54.5 ± 2.1 GPa, was obtained at the 190 V charge voltage, which was due to the high sp3-C content and relatively high residual stress. Similarly, the film deposited at 190 V possessed both low coefficient of friction (COF) and wear rate under various load, indicating that the excellent tribological performance of film could be achieved at 190 V. In addition, the COFs for all films decreased with an increase of load. The present work revealed that the moderate charge voltage value is beneficial for the enhanced wear property of film.

Assessment of carbon net erosion/deposition at the divertor of W7-X

• The net carbon erosion rate at the W7-X divertor is calculated using an analytical erosion model. • Experimentally determined plasma parameters from several discharges and experimental surface roughnesses were used for the calculations. • According to the calculations, during the operational phase OP 1.2a carbon erosion at the strike line was dominated by chemical erosion by oxygen. • Boronizations decreased the oxygen impurity concentration in operational phase OP 1.2b by 1-2 orders of magnitude. This resulted in a decrease of the carbon erosion rate by a factor of about five according to the calculations and in good agreement with experimental values. The net carbon erosion rate at the divertor strike line of W7-X was determined experimentally during the operational phases OP 1.2a and OP 1.2b [M. Mayer et al. Phys. Scr. T171 (2020) 014035; M. Mayer et al., Nuclear Fusion 62 (2022) 126049]. OP 1.2a was characterized by high concentrations of oxygen and a very high net carbon erosion rate. The oxygen concentration decreased by 1-2 orders of magnitude in OP 1.2b due to boronizations, and the experimentally observed erosion rate decreased by a factor of 5-6. The carbon erosion rate at the W7-X divertor is calculated using an analytical erosion model taking physical and chemical erosion by hydrogen, carbon and oxygen impact into account. Experimentally determined plasma parameters from several discharges and experimental surface roughnesses were used for the simulations. The calculated erosion rates for the selected discharges are in reasonable agreement with the experimental values. According to the calculations, during OP 1.2a carbon erosion at the strike line was dominated by chemical erosion by oxygen. The decrease of the oxygen impurity concentration in OP 1.2b decreased the carbon erosion rate by a factor of about five, which is in good agreement with the experimental values. During OP 1.2b carbon erosion was dominated by sputtering by incident hydrogen and carbon ions. The surface morphology has a profound influence on the net carbon erosion rate and develops during a campaign by erosion/deposition phenomena. Plasma-exposed surfaces get smoother with plasma exposure time, which can result in an increase of the erosion yield.

Validation of the Geant4 PIXE component for incident carbon ions

The goal of this study is to experimentally validate PIXE modelling using the Geant4-ANSTO model (“G4-ANSTO”), distributed for the first time in Geant4 11.0, as well as the Geant4 default model (“G4-default”), for targets bombarded with carbon ions of energies up to 3 MeV/amu, an energy range of importance for PIXE applications.The experimental validation was performed using a variety of target materials, spanning a broad atomic number range. The reference experimental measurements were performed at the ANSTO heavy ion microprobe beamline ANTARES. To the authors’ knowledge, this is the first benchmarking investigation for PIXE simulations in Geant4 utilising carbon ions and it is significant for PIXE-based elemental analysis, encompassing archaeological samples, gas samples, environmental and planetary samples for geological and planetary research studies. It is also of relevance for any physics application, requiring the modelling of particle induced atomic de-excitation or atomic de-excitation only.

Monte Carlo Investigation of the Depth-dose Profile of Proton Beams and Carbon Ions in Water, Skeletal Muscle, Adipose Tissue, and Cortical Bone for Hadron Therapy Applications

In this study, the depth-dose profile in water, skeletal muscle, adipose tissue, and cortical bone irradiated using incident beams of protons and carbon ions were simulated at different incident energies using the open source software GEANT4 version 10.3.2 via GATE v.8.0. The depth where the Bragg peaks of protons with incident energies of 75 MeV, 100 MeV, 130 MeV, 150 MeV, and 160 MeV in different materials were determined and the results were compared with the experimental data from the National Institute of Standards and Technology (NIST) database. The corresponding energy for incident carbon ion beam that yields the same Bragg peak position as the incident proton beams were also investigated. The depth-dose profile obtained using carbon ions show better dose conformation, but the presence of dose tail was observed. This suggests that further investigation of the RBE of the secondary fragments is necessary to understand their underlying impact to the carbon ion treatment in general.

Low energy carbon ion induced M X-ray relative intensities for 70Yb, 82Pb and 83Bi

In the present work, the intensity ratios, IMk/IMn (exp) (k = ξ, β, γ, m1; n = αβ, α), for 70Yb, 82Pb and 83Bi induced by the Cq+ (q = 4, 5) ions having energies in the range 800–1500 keV have been measured. These intensity ratios have been compared with those calculated using the ECPSSR model based carbon ion induced Mj (j = 1–5) sub-shell ionization cross sections, the X-ray emission rates based on the Dirac-Fock (DF) model, two sets of the fluorescence and Coster-Kronig yields based on the non-relativistic Hermann-Skillman potential calculations and those based on the relativistic Dirac-Hartree-Slater model. Significant differences observed between the present measured and calculated ratios could be due to multiple-ionization induced in the investigated elements by the incident carbon ions.

Characterization of the Mixed Radiation Field Produced by Carbon and Oxygen Ion Beams of Therapeutic Energy: A Monte Carlo Simulation Study.

Purpose:The main advantages of charged particle radiotherapy compared to conventional X-ray external beam radiotherapy are a better tumor conformality coupled with the capability of treating deep-seated radio-resistant tumors. This work investigates the possibility to use oxygen beams for hadron therapy, as an alternative to carbon ions.Materials and Methods:Oxygen ions have the advantage of a higher relative biological effectiveness (RBE) and better conformality to the tumor target. This work describes the mixed radiation field produced by an oxygen beam in water and compares it to the one produced by a therapeutic carbon ion beam. The study has been performed using Geant4 simulations. The dose is calculated for incident carbon ions with energies of 162 MeV/u and 290 MeV/u, and oxygen ions with energies of 192 MeV/u and 245 MeV/u, and hence that the range of the primary oxygen ions projectiles in water was located at the same depth as the carbon ions.Results:The results show that the benefits of oxygen ions are more pronounced when using lower energies because of a slightly higher peak-to-entrance ratio, which allows either providing higher dose in tumor target or reducing it in the surrounding healthy tissues. It is observed that, per incident particle, oxygen ions deliver higher doses than carbon ions.Conclusions:This result coupled with the higher RBE shows that it may be possible to use a lower fluence of oxygen ions to achieve the same therapeutic dose in the patient as that obtained with carbon ion therapy.

Ultrafast gamma-ray line emission driven by laser-accelerated ion beams

The Monte Carlo code Geant4 is used to demonstrate ultrafast gamma-ray line emission from the 12C +12C reaction driven by laser-accelerated ion beams. With carbon ions of the order of tens of MeV accelerated by laser-bombarding the carbon target, characteristic gamma-ray line emission is generated with durations as short as picoseconds through ultrafast gamma-ray transitions. Because the relative bandwidths of such gamma-ray lines can be reduced to less than 1% and the yield rate of gamma photons is around 10−5 for an incident carbon ion, this gamma-ray line emission can be used as an ultrafast monoenergetic gamma-ray source with a flux of 1.2 × 106 photons/J into 4π. We also show that the bremsstrahlung background induced by electrons accelerated simultaneously with the carbon ions can be mitigated by choosing a proper detection angle and an optimized target thickness.

A carbon CT system: how to obtain accurate stopping power ratio using a Bragg peak reduction technique

In this study, we investigate the performance of the Gunma University Heavy Ion Medical Center’s ion computed tomography (CT) system, which measures the residual range of a carbon-ion beam using a fluoroscopy screen, a charge-coupled-device camera, and a moving wedge absorber and collects CT reconstruction images from each projection angle. Each 2D image was obtained by changing the polymethyl methacrylate (PMMA) thickness, such that all images for one projection could be expressed as the depth distribution in PMMA. The residual range as a function of PMMA depth was related to the range in water through a calibration factor, which was determined by comparing the PMMA-equivalent thickness measured by the ion CT system to the water-equivalent thickness measured by a water column. Aluminium, graphite, PMMA, and five biological phantoms were placed in a sample holder, and the residual range for each was quantified simultaneously. A novel method of CT reconstruction to correct for the angular deflection of incident carbon ions in the heterogeneous region utilising the Bragg peak reduction (BPR) is also introduced in this paper, and its performance is compared with other methods present in the literature such as the decomposition and differential methods. Stopping power ratio values derived with the BPR method from carbon-ion CT images matched closely with the true water-equivalent length values obtained from the validation slab experiment.

Study for online range monitoring with the interaction vertex imaging method

Ion beam therapy enables a highly accurate dose conformation delivery to the tumor due to the finite range of charged ions in matter (i.e. Bragg peak (BP)). Consequently, the dose profile is very sensitive to patients anatomical changes as well as minor mispositioning, and so it requires improved dose control techniques. Proton interaction vertex imaging (IVI) could offer an online range control in carbon ion therapy. In this paper, a statistical method was used to study the sensitivity of the IVI technique on experimental data obtained from the Heidelberg Ion-Beam Therapy Center.The vertices of secondary protons were reconstructed with pixelized silicon detectors. The statistical study used the test of the reconstructed vertex distributions for a given displacement of the BP position as a function of the impinging carbon ions. Different phantom configurations were used with or without bone equivalent tissue and air inserts.The inflection points in the fall-off region of the longitudinal vertex distribution were computed using different methods, while the relation with the BP position was established. In the present setup, the resolution of the BP position was about 4–5 mm in the homogeneous phantom under clinical conditions (106 incident carbon ions). Our results show that the IVI method could therefore monitor the BP position with a promising resolution in clinical conditions.

Growth and optical waveguide fabrication in spinel MgGa2O4 crystal

We report on optical waveguide fabrication in a spinel MgGa2O4 crystal by 6.0MeV carbon ion implantation at a fluence of 2×1015ions/cm2 for the first time to our knowledge. The MgGa2O4 crystal was grown by the floating zone method. The refractive index profile reconstructed by reflectivity calculation method showed that the MgGa2O4 waveguide is a typical barrier waveguide. The typical barrier-shaped refractive index profile is attributed mainly to the nuclear energy deposition of the incident carbon ions into the MgGa2O4 crystal. By performing end-coupling measurements and using the beam propagation method (BPM) for the analysis of the observed modes, it can be concluded that the modes can be confined inside the waveguide.

Modeling the biophysical effects in a carbon beam delivery line by using Monte Carlo simulations

Relative biological effectiveness (RBE) plays an important role in designing a uniform dose response for ion beam therapy. In this study the biological effectiveness of a carbon ion beam delivery system was investigated using Monte Carlo simulation. A carbon ion beam delivery line was designed for the Korea Heavy Ion Medical Accelerator (KHIMA) project. The GEANT4 simulation tool kit was used to simulate carbon beam transporting into media. An incident energy carbon ion beam in the range between 220 MeV/u and 290 MeV/u was chosen to generate secondary particles. The microdosimetric-kinetic (MK) model is applied to describe the RBE of 10% survival in human salivary gland (HSG) cells. The RBE weighted dose was estimated as a function of the penetrating depth of the water phantom along the incident beam direction. A biologically photon-equivalent Spread Out Bragg Peak (SOBP) was designed using the RBE weighted absorbed dose. Finally, the RBE of mixed beams was predicted as a function of the water phantom depth.

Molecular dynamics study of radiation damage and microstructure evolution of zigzag single-walled carbon nanotubes under carbon ion incidence

The radiation damage and microstructure evolution of different zigzag single-walled carbon nanotubes (SWCNTs) were investigated under incident carbon ion by molecular dynamics (MD) simulations. The radiation damage of SWCNTs under incident carbon ion with energy ranging from 25eV to 1keV at 300K showed many differences at different incident sites, and the defect production increased to the maximum value with the increase in incident ion energy, and slightly decreased but stayed fairly stable within the majority of the energy range. The maximum damage of SWCNTs appeared when the incident ion energy reached 200eV and the level of damage was directly proportional to incident ion fluence. The radiation damage was also studied at 100K and 700K and the defect production decreased distinctly with rising temperature because radiation-induced defects would anneal and recombine by saturating dangling bonds and reconstructing carbon network at the higher temperature. Furthermore, the stability of a large-diameter tube surpassed that of a thin one under the same radiation environments.

Irradiation effects in single-walled carbon nanotubes: Density-functional theory based treatments

The collision process of a low-energy carbon ion impinging single-walled carbon nanotubes is studied by using a self-consistent-charge density-functional tight-binding molecular dynamics method. The simulation shows that the outcome of the collision highly depends on the incident kinetic energy and the impact location in the nanotube. There are five types of processes observed: adsorption, reflection, substitution, penetration and damage. The adsorption process becomes dominant at energies lower than 20eV. Defect formation events are observed at energies larger than 20eV. For this process, 5-1DB, 5-8-5, Stone–Wales, 7-4-5-9-5 and 5-7-7-6-5 defects are obtained. The formation processes of the typical defects are described in detail. Moreover, the energy exchange and the charge transfer between the incident carbon ion and the nanotube have also been quantitatively studied.

Collision dynamics of energetic carbon ions impinging on single-walled carbon nanotubes

By employing atomistic simulations based on an empirical potential, we study the collision dynamics of low-energy carbon ions impinging on single-walled carbon nanotubes. We investigate the energy transferred from the incident carbon ions to the target atoms in the nanotubes. We find that the lowest incident energy needed for the primary knock-on atom to be permanently displaced from its original location is 18 eV, and for the secondary knock-on atom to escape out of the nanotube is estimated to be 28 eV. Moreover, we find that the incident threshold energy strongly depends on the diameter of the nanotube and its chirality, and saturates towards the corresponding value in graphene as the tube diameter increases. Furthermore, a single vacancy and an adatom defects are obtained after optimization using the ab-initio calculations.

DOPING OF NANO-SIZED DIAMOND LIKE CARBON FILMS AND THEIR CHARACTERIZATION BY MICRO RAMAN SPECTROSCOPY

Capabilities of the rf plasma beam source in deposition of ultra thin diamond like carbon for the hard disk drive applications have been studied. Nano-sized films were doped by nitrogen, hydrogen and silicon and characterized by micro Raman spectroscopy. Projected ranges of incident carbon ions into the magnetic layer as well as growing film were calculated by Monte Carlo simulation. Ion ranges at 100 eV incident energy were around 0.5 nm. With micro Raman spectroscopy is possible to qualitatively determine optimal deposition parameters and to follow changes in the film properties and carbon binding structure in amorphous matrix with hydrogen, nitrogen and silicon doping elements.

DOPING OF NANO-SIZED DIAMOND LIKE CARBON FILMS AND THEIR CHARACTERIZATION BY MICRO RAMAN SPECTROSCOPY

Capabilities of the rf plasma beam source in deposition of ultra thin diamond like carbon for the hard disk drive applications have been studied. Nano-sized films were doped by nitrogen, hydrogen and silicon and characterized by micro Raman spectroscopy. Projected ranges of incident carbon ions into the magnetic layer as well as growing film were calculated by Monte Carlo simulation. Ion ranges at 100 eV incident energy were around 0.5 nm. With micro Raman spectroscopy is possible to qualitatively determine optimal deposition parameters and to follow changes in the film properties and carbon binding structure in amorphous matrix with hydrogen, nitrogen and silicon doping elements.

Transmission and charge state distribution of carbon ions emerging from nitrogen gas target in a tandem accelerator: Impact of stripper gas pressure

In a tandem accelerator the knowledge of distribution of charge states as well as the overall transmission of incident ions is of great importance for optimized use of the accelerator. We have studied the effect of the stripper gas pressure on the charge state distribution and the transmission of incident carbon ions ($^{12}\mathrm{C}^{1\ensuremath{-}}$) stripped in ${\mathrm{N}}_{2}$ gas target in a tandem accelerator in the energy range of 0.2--1.7 MeV. The observed charge state fractions of the outgoing beam show transition from nonequilibrium to equilibrium distribution as the stripper gas pressure is varied. The experimentally measured average charge values at different stripper gas pressures are compared with an empirical model for the equilibrium average charge. Apart from the charge state distribution, the stripper gas pressure is found to have a more interesting effect in the transmission of incident carbon ions ($^{12}\mathrm{C}^{1\ensuremath{-}}$), which displays a maximum with pressure in the nonequilibrium region. The observed transmission behavior is explained qualitatively.

SU‐E‐T‐281: Secondary Light‐Ions in Carbon‐Ion Therapy: A GEANT4 Simulation of LET and Dose Contributions

The purpose of this investigation was to reveal the dosimetric characteristics and contributions of the secondary light ions produced from carbon-ion beams in water via a GEANT4 simulation. GEANT4 low energy electromagnetic physics processes were used for all ions. The hadronic interactions of protons and neutrons are simulated using low energy elastic interactions while inelastic scattering is simulated with a binary cascade (BIC) model. Other inelastic light-ion interactions are being simulated through the application of a quasi-molecular dynamics (QMD) model. A 27 liter cubic water phantom consisting of 3000 packed rectangular detector sheets (30 cm × 30 cm × 0.1mm) was used in this simulation. A 1 mm diameter pencil beam of 1 million incident carbon-ions was used in all simulations presented. The incident energies per nucleon of the carbon beams studied were selected 155 MeV, 262 MeV and 369 MeV. The energy deposition, total kinetic energy, fluence, and dose averaged LET of each secondary particle produced within each detection sheet was determined to study their variations with depth. The particles investigated were gamma, neutron, electron, positron, proton, deuteron, triton, alpha, He- 3, Li-6, Li-7, Be-7, Be-9, Be-10, B-10, B-1 1, C-1 1, C-12, C-13, C-14, N-13, N-14, N-15, O-16. The relative dose contributions of four secondary ions (B-11, C-1 1, Alpha and Proton) were found to be each greater than 1%. The highest dose averaged LET value was from N-13, though its averaged dose contribution was less than 5×10-4 %. The secondary particles contribute small portion to the total dose deposited from primary carbon beam. Though heavier ions (N, O) show significant higher LET values, their relative dose contributions were negligible.

SU-E-J-80: A Simulation Study with Geant4 on the Yields of Positron-Emitting Nuclei (10C, 11C, and 15O) Induced by Protons and Carbon Ions.

To study the yields and the depth-distributions of positron-emitting nuclei (PEN) 10C, 11C, and 15O induced by protons and carbon ions in PMMA. An application built with various physics packages was constructed with Geant4 Monte Carlo Toolkit. A phantom of 15 cm × 15 cm × 50 cm consisting of PMMA (C5H8O2, density 1.18 g/cm3 ) was irradiated with 70, 110 MeV protons and 204 A, 212.12 A MeV carbonions. Beam quality of 1 cm FWHM with 0.2% Gaussian energy spread FWHM was used. For each beam energy, simulation of the energy deposited was recorded for every 1 mm increment of depth in the phantom. The resulting PEN and their yields were recorded at the production point and also at the point of decay in increments of 1 mm. The overall percentage yields, depth-distributions, and total percentages of PEN per incident particle for both protons and carbon ions were obtained. Our results found that the predominant PMMA fragment was 11C irrespective of incident particle type or energy. Our yields of PEN are comparable with other simulations (FLUKA and MCHIT) as well as existing experimental data. The present work however overestimates the percentage of PEN in the simulations of incident carbon ions and the percentage of 10C for incident protons compared to the experimental data. This particular application built within the Geant4 Monte Carlo Toolkit can estimate the amount of PEN as well as the depth-distributions of these nuclei in hadron induced radiation therapy.

Yields of positron and positron emitting nuclei for proton and carbon ion radiation therapy: A simulation study with GEANT4

A Monte Carlo application is developed to investigate the yields of positron-emitting nuclei (PEN) used for proton and carbon ion range verification techniques using the GEANT4 Toolkit. A base physics list was constructed and used to simulate incident proton and carbon ions onto a PMMA or water phantom using pencil like beams. In each simulation the total yields of PEN are counted and both the PEN and their associated positron depth-distributions were recorded and compared to the incident radiation's Bragg Peak. Alterations to the physics lists are then performed to investigate the PEN yields dependence on the choice of physics list. In our study, we conclude that the yields of PEN can be estimated using the physics list presented here for range verification of incident proton and carbon ions.