Linear Energy Deposition Research Articles

Diamond energy-dispersive dosimeter for measuring linear energy deposition distributions in clinical carbon beam therapy

A thin diamond membrane energy-dispersive dosimeter 50 μm thick was fabricated for estimating clinical dose distribution. In contrast to conventional semiconductors, diamond wide-bandgap semiconductors are expected to have excellent radiation tolerance and biological compatibility based on the linear relationship of stopping power ratio for clinical carbon particles. Linear energy transfer (LET) spectra were obtained along with the Bragg curve for a clinical carbon beam generated at Gunma University Heavy Ion Medical Center. The relative biological effectiveness (RBE) distributions were estimated from the LET spectra for both the mono-energy and spread-out Bragg peak irradiation configurations. The diamond detector was also used as a solid ionization chamber to obtain the radiation-induced current (RIC) distribution, which represents the physical dose distribution. The clinical dose distribution was estimated from the RIC and RBE distributions as proof of concept for the clinical carbon beam therapy field with a single-chip diamond energy-dispersive dosimeter.

Underwater microsecond timescale electrical explosions of aluminum and copper foils

We present results on underwater electrical explosions of thin aluminum and copper foils using a generator delivering ∼200 kA current amplitude, ∼0.9 μs rise time pulses. Time-resolved shadow imaging displays the generation of a strong planar shock wave in water in the vicinity of the exploding foil. Using time-resolved spectroscopy, aluminum oxide (AlO) absorption bands were observed in a Planckian-like spectrum, indicating that aluminum combustion starts when aluminum vaporizes. It is also shown that the strongest shock wave is obtained for the largest linear energy deposition rate to the foil.

METU-DBL: a cost effective proton irradiation facility

The Middle East Technical University Defocusing Beamline (METU-DBL) is designed to deliver protons with selectable kinetic energies between 15–30 MeV, and proton flux between 106–1010 protons/cm2/s, on a maximum 21.55 to 15.40 cm target region with a beam uniformity within ±6%, in accordance with the ESA ESCC No. 25100 specification for single event effects (SEEs) tests in the low energy range. The achieved high proton fluences, allow users to test space-grade materials; electronic circuits, ASICs, FPGAs, optical lenses, structural elements, and coating layers for LEO, GEO, and interplanetary missions.The total received dose on the Device-Under-Test (DUT) from secondary particles created during proton-material interactions at the first beam collimator and the beam dump never exceed 0.1% of the dose from primary protons. The METU-DBL is equiped with several measurement stations and services to the user teams. A secondary measurement station in a rotating drum that can hold multiple samples has been constructed next to the first collimator which provides neutrons for transmission experiments. At the target region, a robotic table is located, which provides mechanical and electrical mounting points to the samples and allows multiple samples to be tested in a row. A modular vacuum box can also be attached on the robotic table for any test that may require a vacuum environment. Power rails on the robotic table provide various outputs for the DUT. For the data acquisition, high-speed networking and a modular industrial PC are available at the target station. The design of the METU-DBL control software enables test users to integrate and optimize the data acquisition and controlling of the DUT.The beam properties at the target region are measured with the diamond, Timepix3, and fiber scintillator detectors mounted on the robotic table. With diamond and Timepix3 detectors, measurements are taken from the five different points (center and the four corners) of the test area to measure the proton flux and ensure that it is uniform across the full test area. Fiber scintillators on both axes (X and Y) scan the target area to cross-check the beam profile's uniformity. Secondary doses during the irradiation are measured by a Geiger-Müller tube sensitive to electrons and gammas above 0.1 MeV and by a neutron detector located at the entrance of the R&D room. The room cools down relatively fast after any irradiation (<1 hour).Accurate linear energy deposition rates and absorbed doses on the samples are calculated using MCNP6, FLUKA and Geant4 Monte Carlo simulations. Alanine dosimetry measurements that are calibrated against these simulations are also used to estimate the absorbed dose on the sample.

Experimental and Simulated Spectral Gamma-Ray Response of a NaI(Tl) Scintillation Detector used in Airborne Gamma-Ray Spectrometry

Abstract. The objective of this work is to simulate the spectral gamma-ray response of NaI(Tl) scintillation detectors for airborne gamma-ray spectrometry (AGRS) using the state-of-the-art multi-purpose Monte Carlo code FLUKA. The study is based on a commercial airborne gamma-ray spectrometry detector system with four individual NaI(Tl) scintillation crystals and a total volume of 16.8 L. To validate the developed model, radiation measurements were conducted using 57Co, 60Co, 88Y, 109Cd, 133Ba, 137Cs and 152Eu calibration point sources with known activities and source-detector geometries under laboratory conditions. In addition, empirical calibration and resolution functions were derived from these measurements combined with additional radiation measurements adopting natural uranium, thorium and potassium volume sources. The simulation results show superior accuracy and precision compared to previous AGRS simulation models with a median relative spectral error &lt; 10 % for most of the radiation sources. Moreover, the implementation of a lower level discriminator model and detailed modelling of the laboratory result in a significant improvement in model accuracy for spectral energies &lt; 100 keV compared to previous studies. Yet thorough statistical analysis incorporating statistical and systematic uncertainty estimates revealed statistically significant deviations between the simulated and measured spectra in the spectral region around the Compton edge, which could be attributed to the scintillator non-proportionality. These findings imply that the linear energy deposition model applied in this and previously developed AGRS simulation models should be revised and considered to be replaced by more accurate non-proportional models.

Reconsidering astrophysical constraints on macroscopic dark matter

Macroscopic dark matter---``macros''---refers to a broad class of alternative candidates to particle dark matter with still unprobed regions of parameter space. These candidates would transfer energy primarily through elastic scattering with approximately their geometric cross section. For sufficiently large cross sections, the linear energy deposition could produce observable signals if a macro were to pass through compact objects such as white dwarfs or neutron stars in the form of thermonuclear runaway, leading to a type Ia supernova or superburst, respectively. We update the constraints from white dwarfs. These are weaker than previously inferred in important respects because of more careful treatment of the passage of a macro through the white dwarf and greater conservatism regarding the size of the region that must be heated to initiate runaway. On the other hand, we place more stringent constraints on macros at a low cross section, using new data from the Montreal White Dwarf Database. New constraints are inferred from the low mass x-ray binary 4U 1820-30, in which more than a decade passed between successive superbursts. Updated microlensing constraints are also reported.

Macroscopic dark matter constraints from bolide camera networks

Macroscopic dark matter (macros) are a broad class of alternative candidates to particle dark matter. These candidates would transfer energy primarily through elastic scattering, and this linear energy deposition would produce observable signals if a macro were to pass through the atmosphere. We produce constraints for low mass macros from the null observation of bolides formed by a passing macro, across two extensive networks of cameras built originally to observe meteorites. The parameter space that could be probed with planned upgrades to the existing array of cameras in one of these networks still currently in use, the Desert Fireball Network in Australia, is estimated.

Numerical Simulations on the Effect and Efficiency of Long Linear Energy Deposition Ahead of a Supersonic Blunt Body: Toward a Laser Spike

The effect of single or repetitive linear energy depositions in front of a supersonic blunt body is computed using the CEDRE flow solver. The CFD Code models the effect of a laser-induced energy deposition, as obtained for example using the long filaments created by a femtosecond laser. Single energy depositions show that significant transient drag reductions are obtained, due to the interaction of the heated core, created by the energy release, with the bow shock. When the deposition is repeated, cumulative effects are important and quasi-steady or unsteady flow regimes are obtained, depending on the power and repetition frequency. This behavior is similar to that obtained with supersonic spiked blunt bodies, acting like a laser spike. This system can lead to 15%-20% fuel savings, depending on the energy deposition efficiency.

Materials Modifications with Cluster Beams: Bulk and Surface Modification

It is now well accepted that electronic excitation and ionization arising from the slowing down of swift heavy ions can lead to structural modifications in some metallic targets as it has been known for a long time in insulators. A rapid overview of some results obtained after GeV monoatomic heavy ion irradiations will be given. It will then be shown that new specific effects take place during irradiations with cluster ions. The projectiles used are energetic cluster beams: 10 to 40 MeV Au4 or C60 ions. The rates of linear energy deposition in electronic excitation are close for GeV monoatomic and for 10 MeV cluster ions, but the cluster ions have characteristic velocities which are one order of magnitude smaller than those of monoatomic ions. This leads to a strong spatial localization of the deposited energy during the slowing down process. The density of deposited energy can then reach values as high as a few 100 eV/atom. This very high density of energy deposited in the electronic system of the targets can lead to spectacular structural modifications: generation in the vicinity of the ion trajectories of isolated or agglomerated point defects, new crystalline phases, amorphized regions... After an overview of such damage induced in bulk metals, semiconductors, and insulators, we will discuss surface damage, consisting in the formation of bumps, craters, lava-flows on the target surface.

Ion beam induced mixing in Pd thin films on silicon

Ion beam mixing of thin palladium layers (50–130 nm) on n-Si(111) substrates, induced by 250–450 keV arsenic ions has been studied. Implantation has been performed at room temperature (RT) to the doses from 0.5–1 × 10 16 ions cm −2. Structural characterization included Rutherford backscattering spectrometry and X-ray diffraction analysis. Our results show that the thickness of the polycrystalline Pd 2Si phase induced by ion bombardment is proportional to the square root of the dose. The high value of F D, the linear energy deposition density at the Pd/Si interface, indicates that the formation of Pd 2Si phase is a diffusion limited process.

Crosslinking yield in particle beam irradiated polystyrene

The crosslinking yields in narrow molecular weight distribution polystyrene bombarded with H + and noble gas ions at energies of 100–400 keV have been compared with yields computed from literature data. The data have been plotted vs the linear energy deposition of the bombarding ions and a threshold located at ca. 10 eV/Å has been found. This curve has been discussed and explained in terms of energy deposited along the ion track and in terms of type and concentration of intermediate chemical species produced by the particle beam passage.

Ion beam mixing in amorphous silicon II. Theoretical interpretation

The ion irradiation-induced intermixing of thin elemental marker layers buried in vapor-deposited amorphous silicon is interpreted by an analytical model based on the theory of random flights and elementary range theory. The general features of ion beam mixing are faithfully described and quantitative predictions of the magnitude of the observed effects are in good agreement with experimental data. The model predicts that the mixing is analogous to thermal diffusion with an effective diffusion coefficient that is proportional to the ion flux and the linear energy deposition density ( F D). The diffusion coefficient is shown to depend on the marker and matrix materials through their atomic masses, atomic numbers and the effective displacement energy of the marker atoms. The model is derived for dilute impurities in a host matrix, but an approximate method for extension to higher concentrations is suggested. The model is shown to be applicable in situations in which the energy deposited per atom is not a large fraction of the heat of fusion of the solid.

Radiobiological Experiments with Heavy Ions at the Bevatron

Penetration of heavy charged particles can be characterized by three basic physical facts: 1) almost no scattering; 2) abrupt increase of linear energy deposition (LET) close to the point where the particles stop; and 3) exact range-energy relationship. These facts constitute the basis of very favorable depth-dose characteristics for heavy ions to be used in radiotherapy. Availability of accelerated high LET heavy ions in the Laboratory, though a recent development, has already provided us with much useful information in physics, chemistry, and radiobiology. Fast heavy ions could previously be studied only in outer space where they form important components of primary cosmic rays. Heavy ions in the Laboratory became available as early as 1957 at the Berkeley HILAC, but at very low energies. In August, 1971, two accelerators, the Princeton Synchrotron1 and the Berkeley Bevatron produced penetrating deflected beams of nitrogen nuclei. Since that time, carbon, oxygen and neon, as well as a few oxygen particles at Princeton, have been accelerated. Stopping-power curves as a function of range for various ions in water, as calculated theoretically, are shown in Figure 1. Various ion energies in units of Mev/nucleon are designated on each curve. The uniformly shaded area represents the stopping-power and associated ions accelerated at the HILAC and cyclotron. The BEVALAC (a compound accelerator formed from the HILAC and Bevatron) adds a new dimension, and initially it will be able to accelerate i ons wi th atomi c no. up to that of iron (Z = 26) to considerable energies.