Distribution Of Heavy Ions Research Articles

Analysis of the Dose Drop at the Edge of the Target Area in Heavy Ion Radiotherapy.

Background The dose distribution of heavy ions at the edge of the target region will have a steep decay during radiotherapy, which can better protect the surrounding organs at risk. Objective To analyze the dose decay gradient at the back edge of the target region during heavy ion radiotherapy. Methods Treatment planning system (TPS) was employed to analyze the dose decay at the edge of the beam under different incident modes and multiple dose segmentation conditions during fixed beam irradiation. The dose decay data of each plan was collected based on the position where the rear edge of the beam began to fall rapidly. Uniform scanning mode was selected in heavy ion TPS. Dose decay curves under different beam setup modes were drawn and compared. Results The dose decay data analysis showed that in the case of single beam irradiation, the posterior edge of the beam was 5 mm away, and the posterior dose could drop to about 20%. While irradiation in opposite direction, the posterior edge of the beam was 5 mm away, and the dose could drop to about 50%. In orthogonal irradiation of two beams, the posterior edge of the beam could drop to about 30-38% in a distance of 5 mm. Through the data analysis in the TPS, the sharpness of the dose at the back edge of the heavy ion beam is better than that at the lateral edge, but the generated X-ray contamination cannot be ignored. Conclusions The effect of uneven CT value on the dose decay of heavy ion beam should also be considered in clinical treatment.

Analysis of radiation-induced transient errors on 7 nm FinFET technology

FinFET technology has recently gained attention in the semiconductor industry due to many benefits it offers, such as lower power consumption, faster performance, and lower static leakage current. However, the behavior of this technology for mission-critical applications where radiation effects are the main concern is not very well known. This work is dedicated to the detailed characterization of radiation-induced transient errors in 7 nm FinFET technology, calculating the sensitivity of basic logic gates implemented using ASAP7 PDK library and predicting the distribution of heavy ions induced Single Event Transient (SET) pulses.

Simulation of irradiation effects with ions on the RFQ linac HIPr

Radiation damage is the limiting factor in the choice of structural materials for advanced fission and fusion reactors. Neutron irradiation of materials is a slow and cost intensive process often extending over several years. Heavy ion irradiation is the only viable means to conduct accelerated testing to assess irradiated microstructures at high dpa levels. In the NRC “Kurchatov Institute” – ITEP the specimens of perspective steels and alloys are irradiated at the RFQ Heavy Ion Prototype (HIPr) by a beam of accelerated heavy ions (Fe, Ti, V, …) up to dose 1017 ions/cm2. During irradiation the investigated specimens can be heated up to 700°C. We have studied the heavy ion distribution on the target. The results of beam profiles measurements for different irradiation modes are presented. To improve the beam control a device was developed and produced. This device is based on the Arduino platform and software for analysing the data received in the streaming mode. The device allows to control all BPM signals together and takes account of these signals for the fluence calculation. Heavy ion irradiated specimens can be analyse with transmission electron microscopy, atom probe tomography and nanoindentation to measure mechanical properties of irradiated surface layers. Results of TEM analysis of Eurofer97 steel irradiated at 300°C to 1016 ions/cm2 are demonstrated.

Forming a uniform distribution of heavy ions on a moving target

A way to obtain a uniform distribution of a heavy-ion beam on a moving target by scanning the beam over the target surface is considered. The scanning is performed by the horizontal and vertical scanner. A method is proposed for calculating the particle density distribution on the target with allowance for the influence of the horizontal slit in front of the target. Since the scanner forces deflecting the center of mass of the beam are periodic, the ion density distribution on the target is also a periodic function in the target motion direction and the spatial period of the function depends on the ratio of the scanner frequencies. With the high-frequency vertical scanner, a rather uniform particle density is obtained on the target despite considerable ion density inhomogeneities in the beam. With the slit, the particle density inhomogeneity on the target sharply increases when the scanned beam goes beyond the slit height.

Studies on heavy charged particle interaction, water equivalence and Monte Carlo simulation in some gel dosimeters, water, human tissues and water phantoms

Some gel dosimeters, water, human tissues and water phantoms were investigated with respect to their radiological properties in the energy region 10keV–10MeV. The effective atomic numbers (Zeff) and electron densities (Ne) for some heavy charged particles such as protons, He ions, B ions and C ions have been calculated for the first time for Fricke, MAGIC, MAGAT, PAGAT, PRESAGE, water, adipose tissue, muscle skeletal (ICRP), muscle striated (ICRU), plastic water, WT1 and RW3 using mass stopping powers from SRIM Monte Carlo software. The ranges and straggling were also calculated for the given materials. Two different set of mass stopping powers were used to calculate Zeff for comparison. The water equivalence of the given materials was also determined based on the results obtained. The Monte Carlo simulation of the charged particle transport was also done using SRIM code. The heavy ion distribution along with its parameters were shown for the given materials for different heavy ions. Also the energy loss and damage events in water when irradiated with 100keV heavy ions were studied in detail.

The heavy ion diffusion region in magnetic reconnection in the Earth's magnetotail

AbstractWhile the plasma in the Earth's magnetotail predominantly consists of protons and electrons, there are times when a significant amount of oxygen is present. When magnetic reconnection occurs, the behavior of these heavy ions can be significantly different from that of the protons, due to their larger gyroradius. In this study, we investigate the heavy ion distribution functions in the reconnection ion diffusion region from a 2.5D three‐species particle‐in‐cell numerical simulation and compare those with Cluster observations from the near‐Earth magnetotail. From the simulation results, we find that the heavy ions are demagnetized and accelerated in a larger diffusion region, the heavy ion diffusion region. The ion velocity distribution functions show that, inside the heavy ion diffusion region, heavy ions appear as counterstreaming beams along z in the GSM x‐z plane, while drifting in y, carrying cross‐tail current. We compare this result with Cluster observations in the vicinity of reconnection regions in the near‐Earth magnetotail and find that the simulation predictions are consistent with the observed ion distribution functions in the ion diffusion region, as well as the inflow, exhaust, and separatrix regions. Based on the simulation and observation results, the presence of a multiscale diffusion region model, for O+ abundant reconnection events in the Earth's magnetotail, is demonstrated. A test particle simulation shows that in the diffusion region, the H+ gains energy mainly through Ex, while the O+ energy gain comes equally from Ex and Ey.

A spectrometer on chemical vapour deposition-diamond basis for the measurement of the charge-state distribution of heavy ions in a laser-generated plasma

This article reports on the development and the first applications of a new spectrometer which enables the precise and time-resolved measurement of both the energy loss and the charge-state distribution of ion beams with 10 < Z < 30 at energies of 4-8 MeV/u after their interaction with a laser-generated plasma. The spectrometer is based on five 20 × 7 mm(2) large and 20 μm thick polycrystalline diamond samples produced via the Chemical Vapour Deposition (CVD) process and was designed with the help of ion-optical simulations. First experiments with the spectrometer were successfully carried out at GSI using (48)Ca ions at an energy of 4.8 MeV/u interacting with a carbon plasma generated by the laser irradiation of a thin foil target. Owing to the high rate capability and the short response time of the spectrometer, pulsed ion beams with 10(3)-10(4) ions per bunch at a bunch frequency of 108 MHz could be detected. The temporal evolution of the five main charge states of the calcium ion beams as well as the corresponding energy loss values could be measured simultaneously. Due to the outstanding properties of diamond as a particle detector, a beam energy resolution ΔEE ≈ 0.1% could be reached using the presented experimental method, while a precision of 10% in the energy loss and charge-state distribution data was obtained.

Width of the equilibrium charge distribution of heavy ions in solid and gaseous media

Based on an analysis of the experimental data on the charge distributions of ions in gases and solids, the analytical parameterization of the width of the charge distribution as a function of the energy, the average equilibrium ion charge, ion nuclear charge, and nuclear charge of target atom has been obtained. The proposed relations are applicable in a broad energy range and describe the existing experimental data satisfactorily.

Empirical estimation of the equilibrium charge distribution of heavy ions in solid and gaseous media

Abstract Based on the analysis of experimental data on equilibrium charge distributions of ions in gases and solid media, the analytical parameterization of the charge distribution width as a function of the average ion charge and nuclear charges of the ion and the target atom and that of the asymmetry as a function of the average ion charge are obtained. The proposed relations are applicable in a broad energy interval and describe the existing experimental data satisfactorily.

Fast Data Acquisition in Heavy Ion CT Using Intensifying Screen—EMCCD Camera System With Beam Intensity Monitor

We investigated the feasibility of fast data acquisition in heavy ion CT (IonCT) technique with an X-ray intensifying screen-charged coupled device (CCD) camera system. This technique is based on measuring the residual range distribution of heavy ions after passing through an object. We took a large number of images with a CCD camera for one projection by changing the range shifter (RS) thickness to obtain a characteristic curve similar to a Bragg curve and then to estimate the relative residual range. We used a high quality Electron Multiplying CCD (EMCCD) camera, which drastically reduced data acquisition time. We also used a parallel-plate ionization chamber upstream of an object to monitor the time variation in heavy ion beam intensity from a synchrotron accelerator and to perform beam intensity correction for all EMCCD images. Experiments were conducted using a broad beam of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> C, which was generated by spreading out the pencil beam accelerated up to 400 MeV/u by the Heavy Ion Medical Accelerator, in Chiba (HIMAC) at the National Institute of Radiological Sciences, with a scatterer. We demonstrated that a fast CT data acquisition, 14 min for 256 projections, is possible for an electron density phantom, consisting of six rods with a relative electron density resolution of 0.017, using the proposed technique with HIMAC.

FIRST MEASUREMENTS OF THE COMPLETE HEAVY-ION CHARGE STATE DISTRIBUTIONS OF C, O, AND Fe ASSOCIATED WITH INTERPLANETARY CORONAL MASS EJECTIONS

We present the first analysis of the complete charge state distributions of heavy ions in interplanetary coronal mass ejections (CMEs), from singly charged to fully ionized. We develop a novel analysis technique that requires the combination and cross-calibration of two different data sets from the Solar Wind Ion Composition Spectrometer on the Advanced Composition Explorer. The first contains ions of higher charge states, and includes an identification of their mass, mass-per-charge, and energy-per-charge. The second data set contains singly and low-charge ions, and identifies only their mass-per-charge and energy-per-charge. Focusing on C, O, and Fe, we find ionic charge states representative of temperatures from ≤60,000 K to over 5,000,000 K contained within interplanetary CMEs observed near 1 AU. We interpret these data in the context of near-Sun observations of filament material associated with CMEs. We find that singly charged ions are embedded within selected interplanetary CMEs, and we examine their densities and durations. These data thus provide the most unambiguous in situ diagnostic of solar prominence plasma in the heliosphere.

Ion distributions in the vicinity of Mars: Signatures of heating and acceleration processes

More than three years of data from the ASPERA-3 instrument on-board Mars Express has been used to compile average distribution functions of ions in and around the Mars induced magnetosphere. We present samples of average distribution functions, as well as average flux patterns based on the average distribution functions, all suitable for detailed comparison with models of the near-Mars space environment. The average heavy ion distributions close to the planet form thermal populations with a temperature of 3 to 10 eV. The distribution functions in the tail consist of two populations, one cold which is an extension of the low altitude population, and one accelerated population of ionospheric origin ions. All significant fluxes of heavy ions in the tail are tailward. The heavy ions in the magnetosheath form a plume with the flow aligned with the bow shock, and a more radial flow direction than the solar wind origin flow. Summarizing the escape processes, ionospheric ions are heated close to the planet, presumably through wave-particle interaction. These heated populations are accelerated in the tailward direction in a restricted region. Another significant escape path is through the magnetosheath. A part of the ionospheric population is likely accelerated in the radial direction, out into the magnetosheath, although pick up of an oxygen exosphere may also be a viable source for this escape. Increased energy input from the solar wind during CIR events appear to mainly increase the number flux of escaping particles, the average energy of the escaping particles is not strongly affected. Heavy ions on the dayside may precipitate and cause sputtering of the atmosphere, though fluxes are likely lower than 0.4 × 1023 s−1.

Spatial and angular distribution of the heavy ion charge under channeling in crystals

A kinetic theory of passage of multiply charged heavy ions through crystals is developed that allows for diffusion in the transverse momentum space and ion-crystal charge exchange. The theory provides an adequate explanation for the observed angular distributions of heavy ions passing through oriented crystals, makes it possible to calculate the partial angular distributions of different charge states, and treats the discovered effects of “cooling” and “heating” of channeled ion beams in physical terms. The angular and spatial distribution of channeled ions with different energies is calculated. Whether a channeled beam of multiply charged heavy ions will be cooled or heated is related to the dependence of the electron capture and loss probabilities on the impact parameter when the ions interact with atomic chains. This interaction governs the run of the angular and spatial distribution of the channeled ion charge.

Influence of the gap-target configuration on the measured energy loss of C-ions in Ar-gas and -plasma

Plasma targets for measuring energy loss and charge state distribution of heavy ions in non-ideal Ar-plasmas ( Γ -parameters 0.55–1.5) have been developed and the interaction with several ion species, C, Ar, Xe at 5.9 MeV / u , was studied. Here the results for 5.9 MeV / u C-ions are presented which have been understood just recently by considering the gas dynamics in the target due to the special configuration with the gap interaction zone for the plasma, which can be also simulated by the VarJet code.

Nonuniformity of the chemical composition of a capillary discharge plasma

A steady-state distribution of the concentration of two ion species in a capillary discharge plasma is studied using MHD equations for a plasma with a spatially nonuniform, time-dependent chemical composition. In our case, the set of equations is significantly simplified because of the steady-state character and symmetry of the problem. Even with such simplification, however, some results could be obtained only by numerical integration. The factors affecting the distribution of heavy ions are studied. It is shown that the distribution of the heavy impurity over the discharge cross section can be much more nonuniform than the distribution of the main component (hydrogen). A simple criterion for such a nonuniformity is obtained.

Shockwave-driven, non-ideal plasmas for interaction experiments with heavy-ion beams

Plasma targets for measuring energy loss and charge-state distribution of heavy ions in non-ideal plasmas have been developed. Ar plasmas with Γ-parameters 0.55–1.5 could be realized and the interaction with several ion species studied. Here, the results for 5.9 MeV/u C ions are presented. The energy loss in plasma was reproduced in different experiments.

Statistical theory of charge state distributions of channeled heavy ions

On the basis of the kinetic equations, a theory of transmission of multiply charged heavy ions through crystals is developed. It takes into account both diffusion in transverse momentum and charge exchange. The theory gives an adequate description of observed angular distributions of heavy ions transmitted through a crystal, allows calculation of the partial angular distributions of the various charge states, and gives a physical explanation of the so called cooling maxima and the heating minima in the angular distributions. The occurrence of cooling or heating effects and the detailed structure of the angular distribution depend on both the impact parameter dependence of the probabilities for electron capture and loss and on the relative contributions from different charge states. Since the angular distributions can be very different for different charge states, the structure of the total distribution can be quite complex.

A statistical study of oxygen freezing‐in temperature and energetic particles inside magnetic clouds observed by Ulysses

Interplanetary Coronal Mass Ejections (ICMEs) have proven to be very complex phenomena, not easy to unveil using a single set of observations. We combine Ulysses observations of medium energy particles, solar wind plasma parameters, magnetic field, and charge state distributions of heavy ions in order to identify and characterize CME ejecta in the heliosphere. We focused on a special class of ICMEs, so‐called magnetic clouds (MC). The large number of MCs detected by Ulysses allowed us to perform a statistical analysis of the freezing‐in temperature and energetic particle population within MCs. Based on a larger statistical set of events covering a full solar cycle and all heliolatitudes, we can confirm previous findings of a significant temperature increase within MCs. Furthermore, we found that this increase occurs at all latitudes and phases of the solar cycle. Intensities of medium‐energy particles are generally depleted or not changed inside the MCs. This behavior is, again, found at all latitudes and solar cycle phases.

Formation of the charge and energy distributions of heavy ions in a material in the diffusion model

We investigate the formation of the charge and energy distributions of ions that slow down and randomly change their charges in collisions with particles of the medium. We study the influence that the spread of ions in charge has on the shape of the Bragg curve. The suggested diffusion approximation for the kinetic equation of heavy ions allows the parameters of the ion charge and energy distributions to be easily determined in the entire ion path. The parameters of the ion charge distribution are shown to be related to the ionization-recombination cross sections. The ion distributions calculated in the suggested analytical model are compared with the results of numerical calculations. We have obtained good agreement between the analytical, numerical, and experimental results.

Charge state distributions of heavy ions after scattering at surface atoms

The charge state distributions (CSDs) of Li, C and F ions after a single collision with Au atoms deposited as a submonolayer coverage on Si were measured at energies below 500 keV/amu and compared to the equilibrium CSDs. The influence of the surface on the charge state of the outgoing ions is demonstrated for Li ions at 3 MeV. It is found that the CSD after a single collision is generally different from the equilibrium distribution.