Path Of Heavy Ion Research Articles

Transport process and energy loss of heavy ions in silicon carbide

Using the Monte Carlo method, the energy losses in silicon carbide of heavy ions with different linear energy transfers (LETs) are simulated and calculated. The simulation results show that the energy loss per unit depth of heavy ions in silicon carbide is affected by both the ion energy and the incident depth. Primary heavy ions and secondary electrons mainly cause energy loss, and the non-ionization energy loss only accounts for about 1% of the total energy loss. With the increase of LET, the initial angle and energy distribution of the secondary electrons become more and more concentrated. The peak position of the generated charge deposition is in the center of the heavy-ion track, and the distribution is linearly decreasing in Gaussian form in the direction perpendicular to the incident depth. In the californium source experiment of SiC MOSFET, when the drain voltage is 480 V, the device has a single event burnout, and the breakdown voltage of SiC MOSFET is less than 1 V after burnout has occurred. With the experimental results, we carry out the TCAD simulation of SiC MOSFET and obtain the electric field distribution inside the device under different drain voltages. The electric field parameters are used in the Monte Carlo simulation of SiC MOSFET with considering the metal layer. It is found in the Monte Carlo simulation that the greater the electric field of the epitaxial layer, the longer the path of heavy ions moving on the epitaxial layer is and the more the deposited energy, and that the secondary electrons are more likely to move in the direction of the electric field as the electric field increases, resulting in excessive energy deposition in local areas.

Mechanical properties of swift heavy ion irradiated Y3Al5O12 single crystal

The present investigation is devoted to the study of the nano-mechanical properties of Y3Al5O12 single crystal irradiated with swift heavy ions using nano-indentation technique. The irradiations were performed at GANIL accelerator, Caen, France with 561 MeV 51Cr, 90 MeV 51Cr ions, 278 MeV 128Te, 193 MeV 208Pb and 885 MeV 238U ion beams. The electronic stopping power Se range is from 6 keV/nm to 46 keV/nm. The nano-indentation tests reveal that both hardness and Young’s modulus decrease with fluence and reach a saturation value depending on the ion species and electronic stopping power. From the comparison with our earlier experimental data obtained using X-ray diffraction (XRD), and atomic force microscopy (AFM) measurements, we conclude that the hardness and Young’s modulus modification is related to the stress level created along the swift heavy ion path.

Biophysics Model of Heavy-Ion Degradation of Neuron Morphology in Mouse Hippocampal Granular Cell Layer Neurons.

Exposure to heavy-ion radiation during cancer treatment or space travel may cause cognitive detriments that have been associated with changes in neuron morphology and plasticity. Observations in mice of reduced neuronal dendritic complexity have revealed a dependence on radiation quality and absorbed dose, suggesting that microscopic energy deposition plays an important role. In this work we used morphological data for mouse dentate granular cell layer (GCL) neurons and a stochastic model of particle track structure and microscopic energy deposition (ED) to develop a predictive model of high-charge and energy (HZE) particle-induced morphological changes to the complex structures of dendritic arbors. We represented dendrites as cylindrical segments of varying diameter with unit aspect ratios, and developed a fast sampling method to consider the stochastic distribution of ED by δ rays (secondary electrons) around the path of heavy ions, to reduce computational times. We introduce probabilistic models with a small number of parameters to describe the induction of precursor lesions that precede dendritic snipping, denoted as snip sites. Predictions for oxygen (16O, 600 MeV/n) and titanium (48Ti, 600 MeV/n) particles with LET of 16.3 and 129 keV/μm, respectively, are considered. Morphometric parameters to quantify changes in neuron morphology are described, including reduction in total dendritic length, number of branch points and branch numbers. Sholl analysis is applied for single neurons to elucidate dose-dependent reductions in dendritic complexity. We predict important differences in measurements from imaging of tissues from brain slices with single neuron cell observations due to the role of neuron death through both soma apoptosis and excessive dendritic length reduction. To further elucidate the role of track structure, random segment excision (snips) models are introduced and a sensitivity study of the effects of the modes of neuron death in predictions of morphometric parameters is described. An important conclusion of this study is that δ rays play a major role in neuron morphological changes due to the large spatial distribution of damage sites, which results in a reduced dependence on LET, including modest difference between 16O and 48Ti, compared to damages resulting from ED in localized damage sites.

Effect of Recombination between a Molecular Ion and an Electron on Radial Dose in the Irradiation of a Heavy Ion

<p class="1Body">This paper discusses the effect of recombination between a molecular ion and a free electron on radial dose in the irradiation of a heavy ion through simulations. This irradiation produces molecular ions and free electrons due to the heavy ion impact ionization. The composition electric field, which is formed from these molecular ions, traps some of free electrons and these trapped free electrons increase radial dose near the heavy ion path. These trapped electrons also cause the recombination and that the recombination enhances radial dose.</p>

Direct manipulation of the uncompensated antiferromagnetic spins in exchange coupled system by GeV ion irradiation

Incident ion energy to matrix electrons of a material is dissipated within a narrow cylinder surrounding the swift heavy ion path. The temperature of the lattice exceeds the melting point and upon quenching causes nanometric modifications. We present here a unique ex situ approach in manipulating the uncompensated spins in antiferromagnetic layers of ferro-/antiferromagnetic exchange coupled systems on a nanometric scale. We use the impact of relativistic heavy ion (1–2 GeV) irradiation on such systems. We find an increase in the bias field and a restoration of the reversal via domain nucleation in the trained state. These are identified as plausible results of ion-induced antiferromagnetic ordering with little or no effect on the layer structure. This study demonstrates, therefore, the possibility of nanoscale tailoring of exchange coupled systems that survive even in the trained state.

Nuclear interactions in heavy ion transport and event-based risk models

The physical description of the passage of heavy ions in tissue and shielding materials is of interest in radiobiology, cancer therapy and space exploration, including a human mission to Mars. Galactic cosmic rays (GCRs) consist of a large number of ion types and energies. Energy loss processes occur continuously along the path of heavy ions and are well described by the linear energy transfer (LET), straggling and multiple scattering algorithms. Nuclear interactions lead to much larger energy deposition than atomic-molecular collisions and alter the composition of heavy ion beams while producing secondary nuclei often in high multiplicity events. The major nuclear interaction processes of importance for describing heavy ion beams was reviewed, including nuclear fragmentation, elastic scattering and knockout-cascade processes. The quantum multiple scattering fragmentation model is shown to be in excellent agreement with available experimental data for nuclear fragmentation cross sections and is studied for application to thick target experiments. A new computer model, which was developed for the description of biophysical events from heavy ion beams at the NASA Space Radiation Laboratory (NSRL), called the GCR Event Risk-Based Model (GERMcode) is described.

Radial dose distribution around a heavy ion's path

Ionization currents produced in a small wall-less ionization chamber located at varying distance from the 200 MeV Ni 12+ ion's path traversing Ar gas were measured and utilized to construct a track structure model. Using the LET value of 200 MeV Ni 12+ and G(Fe 3+) in Fricke solutions (= 15.4) for fast electrons, we estimate G(Fe 3+) for 200 MeV Ni 12+ to be 5.0.

Track structure and radiation transport model for space radiobiology studies

Radiobiology experiments performed in space are deemed necessary for validation of risk-assessment methods. The understanding of space radiobiology experiments must combine knowledge of the space radiation environment, radiation transport, and models of biological response. The heavy ion transport code HZETRN has recently been combined with improved models of the galactic cosmic rays (GCR) and extensive comparisons made to measurements on the space shuttle with a tissue equivalent, proportional counter. HZETRN was also coupled with track-structure models of biological damage from heavy ions. Track-structure calculations using improved models of the radial dose distribution around the path of heavy ions provide a good description of ground-based experiments for inactivation cross sections. Therefore, we use these models to predict inactivation of Bacillus Subtilis spores in space. Calculations consider single-particle effects, as well as the background from low linear energy transfer ions of the GCR and trapped radiations on the radial distributions of effects measured in plastic detectors.

Predicting decay in free-radical concentration in L-α-alanine following high-LET radiation exposures

Efforts have been made to develop a model that will predict time-dependent decay in radiation-induced free-radical concentration in L-α-alanine following heavy-charged-particle exposures. The decay rate depends on radiation quality, dose and dose-rate. For low doses, the decay-rate is approx. 0.5 and 1.5% per year following 60Co λ-ray exposures and Linac-produced x-ray or electron exposures. Decay rates, however, have been found to increase as measured from low average doses, sparse single tracks, of heavy charged particles. We have compared measured decay after exposures to low average doses from high-LET particles with predicted decay calculated as function of particle velocity and charge and detector parameters. The predicted decay is obtained by folding measured decay after Linac-produced electron exposures of very high doses into the calculated dose distribution around the heavy ion's path. Preliminary results show agreement between the experimental data and results obtained from this model, within the experimental uncertainty.

Track “core” effects in heavy ion radiolysis

By assuming that HO . 2 radical production in water and H 2 production in benzene are 2 hit processes, and applying the concepts of track physics, we are able to obtain a parameteric fit to the yields of these reactions by heavy ion radiolysis from knowledge of the radial dose distribution about a heavy ion's path. We make no use of the concept of a track core, for no clearly definable track core appears in our calculations of the radial dose distribution. Instead we calculate an action cross section σ from the assumed 2 hit response to γ-rays. The cross section is calculated from two fitted parameters, E 0, the γ-ray dose at which there is an average of 1 hit per target, and the target radius a 0. From the cross section, the target radius and the stopping power we calculate the G value. While our model is not mechanistic, the assumed 2 hit process is consistent with hypotheses which have been offered as chemical models for these processes. Since a 2 hit process is more likely to take place in a high dose region, close to an ion's path, it may easily be attributed to a hypothetical track core in energy deposition, when indeed the response is a property of the detector.

Heavy-Ion Track Structure in Silicon

The energy deposition in the vicinity of a heavy ion path in silicon has been investigated by a Monte Carlo transport analysis of the delta rays produced along the track. The dose as a function of radial distance is presented for C, A1, and Fe ions with energies between 10 and 10,000 MeV. The average dose in cylinders of radii between 10-3 and 1 μm as a function of the distance of the cylinder from the path is also presented.

Spatial Energy Distribution around Heavy-Ion Path

A theoretical model to calculate radial energy deposition, around a heavy-ion path, has been presented. The method of calculation involves evaluation of energy deposition through such basic process...