Broad Energy Spectrum Research Articles

Gallium nitride (GaN) devices as a platform technology for radiation hard inertial confinement fusion diagnostics.

Inertial Confinement Fusion (ICF) is undergoing more detailed research to increase neutron yield and will require high resolution imaging near the target. Neutron damage to diagnostics remains a serious issue in understanding and achieving ICF. We have demonstrated that Gallium Nitride (GaN) optoelectronic devices have exceptional neutron radiation hardness, by systematic testing of neutron radiation effects in GaN devices and materials with elevated neutron fluence levels and a broad neutron energy spectrum. During the 2013-2017 run cycles at Los Alamos Neutron Science Center (LANSCE), we irradiated various GaN materials and devices with fast and thermal plus resonance neutrons at several beamlines. This paper presents a radiation hardness study for Aluminum Gallium Nitride and Gallium Nitride (AlGaN/GaN) deep UV LEDs irradiated at the LANSCE 4FP60R beamline. The fluence level was up to 2.4 × 1013 neutrons/cm2 for neutrons with energies greater than 0.1 MeV. The device performance was monitored in real time. After three years of irradiation studies, we found that the GaN devices maintained operation in the forward active region. The current and voltage relation (I-V curves) varied insignificantly in the linear region. Our results demonstrate the radiation hardness needed for laser fusion diagnostics at least up to 1017 neutron yield per shot, if the diagnostics is placed 1 m away from the target, where the neutron fluence per shot is approximately 8 × 1011 n/cm2. The GaN devices can operate for multiple shots.

Transport and analysis of electron beams from a laser wakefield accelerator in the 100 MeV energy range with a dedicated magnetic line

Electron bunches generated by laser driven wakefield acceleration are transported and analyzed using a magnetic line composed of a triplet of quadrupoles and a dipole. Short pulse bunches with a total charge of ≈130pC, and broad band energy spectra in the range 45 to 150MeV are generated by ionization assisted injection in a gas cell. The electron source is imaged about one meter away from the exit of the gas cell by the magnetic line, delivering electron bunches at a stable position in the image plane where a charge density of ≈2.9pC∕mm2 at an energy of 69.4±0.6MeV is achieved. This magnetic line improves dramatically the accuracy of energy determination of this electron source, leading to an energy error as low as 8.6‰ in the 70MeV range for 5mrad divergence electron bunch and considering the resolution of the entire detection system. The transport of bunches with improved stability and energy selection paves the way to various applications including multi-stage laser plasma acceleration.

Attosecond coherent control of oxygen dissociation by XUV-IR laser fields using three-dimensional momentum imaging

Author(s): Ranitovic, P; Sturm, FP; Tong, XM; Wright, TW; Ray, D; Zalyubovskya, I; Shivaram, N; Belkacem, A; Slaughter, DS; Weber, T | Abstract: We have performed ultrafast three-dimensional ion momentum imaging spectroscopy on the dissociative single ionization of oxygen molecules using attosecond pulse trains with a broad energy spectrum of 5-30 eV. High-resolution momentum imaging allows clear identification of vibrational structures corresponding to the predissociation of highly excited cationic states. By adding a pump infrared field that is synchronized with and polarized orthogonally to the XUV pulse train, and an additional probe IR field, we demonstrate how the yield of O+ ions can be steered between different dissociation channels by coherently controlling the coupling between multiple O2+∗ electronic states on an attosecond time scale. Time-dependent calculations in a single active electron approximation allow a qualitative analysis of ion yields for two orientations of the molecular axis.

Slowing-down and stopped charged particles cause angular dependence for absorbed dose measurements

The space radiation environment is dominated by heavy charged particles with atomic numbers ranging from 1 to 93, with broad energy spectra that exceed 10 GeV per nucleon. Despite advances in space radiation modeling and transport, radiation detectors continue to provide critical data for understanding risks of health effects to astronauts in space. In the past, NASA relied on tissue-equivalent proportional counters and passive devices for operational dosimetry; however, in recent years, pixel detectors providing detailed information about the radiation environment through analysis of charged particle tracks have been demonstrated in space. These next-generation detectors, based on Timepix read-out technology, require special analysis considerations that were not necessary or possible for previous dosimetry tools. The impacts of slowing-down and stopped ions on absorbed dose measurements must be explicitly modeled to understand variations with detector orientation. The purpose of the present study is to conclusively demonstrate that while absorbed dose measurements of penetrating charged particles are independent of detector orientation, slowing-down and stopped particles can result in charged particle absorbed dose measurements that are dependent on detector orientation. Monte Carlo simulations of an unshielded detector, irradiated at selected orientations by different kinetic energy domains with fluence spectra representative of two historical solar particle events, are presented to demonstrate the dependence of absorbed dose measurements. Next, results from Monte Carlo simulations of the same energy domains and fluence spectra, isotropically impinging on an anisotropic shield configuration about the detector, are shown, to exhibit the potential for observing varying absorbed doses under realistic environment and shielding conditions. Finally, slowing-down and stopped proton data acquired with Timepix-based detectors at the Tandem Van de Graaff at Brookhaven National Laboratory are used to demonstrate the effect via accelerator-based measurements.

Efficient monoenergetic proton beam from ultra-fast laser interaction with nanostructured targets

The broad energy spectrum of laser-accelerated proton beams is the most important difficulty associated with such particle sources on the way to future applications such as medical therapy, proton imaging, inertial fusion, and high-energy physics. The generation of proton beams with enhanced monoenergetic features through an ultra-intense laser interaction with optimized nanostructured targets is reported. Targets were irradiated by 40 fs laser pulses of intensity 5.5×1020 W cm−2 and wavelength 1 μm. The results of multi-parametric Particle-in-Cell calculations showed that proton beams with considerably reduced energy spread can be obtained by using the proposed nanostructured target. At optimized target dimensions, the proton spectrum was found to exhibit a narrow peak at about 63 MeV with a relative energy spread of ΔE/Epeak∼ 5% which is efficiently lower than what is expected for unstructured double layer targets (∼70%).

Energy-resolved fast neutron resonance radiography at CSNS

The white neutron beamline at the China Spallation Neutron Source will be used mainly for nuclear data measurements. It will be characterized by high flux and broad energy spectra. To exploit the beamline as a neutron imaging source, we propose a liquid scintillator fiber array for fast neutron resonance radiography. The fiber detector unit has a small exposed area, which will limit the event counts and separate the events in time, thus satisfying the requirements for single-event time-of-flight (SEToF) measurement. The current study addresses the physical design criteria for ToF measurement, including flux estimation and detector response. Future development and potential application of the technology are also discussed.

Optimizing the Parameters of Zr Alloy Doping with Al, Fe, and Mo via the Irradiation of Respective Films on Zr Surfaces Using Ar Ions

The effect the sputtering of a film–substrate system has on the modification of near-surface layers of zirconium alloy E110 (Zr–1% Nb) in the ionic mixing regime upon irradiation by a beam of argon ions with a wide energy spectrum is considered. It is shown that to increase the atoms’ efficiency of penetration and achieve the optimum doping conditions via ionic mixing upon irradiation by a beam of ions with a broad energy spectrum, the ion energy in the beam must be increased while simultaneously lowering the reduced atomic beam mass by using a combined ion beam of different masses.

Energy Selection in Nonadiabatic Transitions.

In this work we investigate whether and how a molecule undergoing a nonadiabatic transition can show different energy mean values and distributions in the two electronic states that are populated. We analyze three models, of which models I and II mimick the limiting cases of almost adiabatic and almost diabatic regimes, respectively, and are solvable by first-order perturbation theory. Model III represents realistically the photodissociation of a diatomic molecule and is treated numerically. The three models provide a consistent picture of the energy selection effect. For a typical avoided crossing, the wavepacket component that undegoes the transition between the two adiabatic states has a larger mean value of energy than the other component, both for upward and for downward transitions. The analysis of model II shows that the Landau-Zener rule can be deduced in a fully quantum mechanical way. We believe that the energy selection effect can be observed experimentally in the photodissociation of diatomic molecules. The effect should be particularly relevant for wavepackets endowed with a broad energy spectrum, as the result of excitation with ultrashort light pulses.

High energy proton induced radiation damage of rare earth permanent magnet quadrupoles.

Permanent magnet quadrupoles (PMQs) are an alternative to common electromagnetic quadrupoles especially for fixed rigidity beam transport scenarios at particle accelerators. Using those magnets for experimental setups can result in certain scenarios, in which a PMQ itself may be exposed to a large amount of primary and secondary particles with a broad energy spectrum, interacting with the magnetic material and affecting its magnetic properties. One specific scenario is proton microscopy, where a proton beam traverses an object and a collimator in which a part of the beam is scattered and deflected into PMQs used as part of a diagnostic system. During the commissioning of the PRIOR (Proton Microscope for Facility for Antiproton and Ion Research) high energy proton microscope facility prototype at Gesellschaft für Schwerionenforschung in 2014, a significant reduction of the image quality was observed which was partially attributed to the demagnetization of the used PMQ lenses and the corresponding decrease of the field quality. In order to study this phenomenon, Monte Carlo simulations were carried out and spare units manufactured from the same magnetic material-single wedges and a fully assembled PMQ module-were deliberately irradiated by a 3.6 GeV intense proton beam. The performed investigations have shown that in proton radiography applications the above described scattering may result in a high irradiation dose in the PMQ magnets. This did not only decrease the overall magnetic strength of the PMQs but also caused a significant degradation of the field quality of an assembled PMQ module by increasing the parasitic multipole field harmonics which effectively makes PMQs impractical for proton radiography applications or similar scenarios.

Neutron Spectrum Measured by Activation Diagnostics in Deuterium Gas-Puff Experiments on the 3 MA GIT-12 Z-Pinch

A set of neutron diagnostics including scintillation time-of-flight detectors, bubble detectors, and several kinds of threshold nuclear activation samples is used to obtain information about the yield and spectrum of the neutrons produced by a deuterium gas-puff z-pinch. The experiments are performed at a current of about 3 MA on the GIT-12 generator at the Institute of High Current Electronics of the Siberian Branch of Russian Academy of Sciences in Tomsk. The average neutron yield in the experiments in 2016 was $2.3 \times 10^{12}$ neutrons per single shot. Using the data obtained with the help of neutron activation diagnostics, the time-of-flight detectors have been absolutely calibrated and the broad energy spectrum of the produced neutrons was evaluated. By the calculations presented in this paper, due to the multi-MeV energies of deuterons generated in the pinch, up to 15% of the total neutron yield could be produced by nuclear reactions of deuterons with a stainless steel vacuum chamber and aluminum components of the diagnostic apparatus inside the chamber.

Scale-up of a Luminescent Solar Concentrator-Based Photomicroreactor via Numbering-up.

The use of solar energy to power chemical reactions is a long-standing dream of the chemical community. Recently, visible-light-mediated photoredox catalysis has been recognized as the ideal catalytic transformation to convert solar energy into chemical bonds. However, scaling photochemical transformations has been extremely challenging due to Bouguer–Lambert–Beer law. Recently, we have pioneered the development of luminescent solar concentrator photomicroreactors (LSC-PMs), which display an excellent energy efficiency. These devices harvest solar energy, convert the broad solar energy spectrum to a narrow-wavelength region, and subsequently waveguide the re-emitted photons to the reaction channels. Herein, we report on the scalability of such LSC-PMs via a numbering-up strategy. Paramount in our work was the use of molds that were fabricated via 3D printing. This allowed us to rapidly produce many different prototypes and to optimize experimentally key design aspects in a time-efficient fashion. Reactors up to 32 parallel channels have been fabricated that display an excellent flow distribution using a bifurcated flow distributor (standard deviations below 10%). This excellent flow distribution was crucial to scale up a model reaction efficiently, displaying yields comparable to those obtained in a single-channel device. We also found that interchannel spacing is an important and unique design parameter for numbered-up LSC-PMs, which influences greatly the photon flux experienced within the reaction channels.

Distribution uniformity of laser-accelerated proton beams**Supported by National Natural Science Foundation of China (11575011, 61631001) and National Grand Instrument Project (2012YQ030142)

Compared with conventional accelerators, laser plasma accelerators can generate high energy ions at a greatly reduced scale, due to their TV/m acceleration gradient. A compact laser plasma accelerator (CLAPA) has been built at the Institute of Heavy Ion Physics at Peking University. It will be used for applied research like biological irradiation, astrophysics simulations, etc. A beamline system with multiple quadrupoles and an analyzing magnet for laser-accelerated ions is proposed here. Since laser-accelerated ion beams have broad energy spectra and large angular divergence, the parameters (beam waist position in the Y direction, beam line layout, drift distance, magnet angles etc.) of the beamline system are carefully designed and optimised to obtain a radially symmetric proton distribution at the irradiation platform. Requirements of energy selection and differences in focusing or defocusing in application systems greatly influence the evolution of proton distributions. With optimal parameters, radially symmetric proton distributions can be achieved and protons with different energy spread within ±5% have similar transverse areas at the experiment target.

A light-weight compact proton gantry design with a novel dose delivery system for broad-energetic laser-accelerated beams

Proton beams may provide superior dose-conformity in radiation therapy. However, the large sizes and costs limit the widespread use of proton therapy (PT). The recent progress in proton acceleration via high-power laser systems has made it a compelling alternative to conventional accelerators, as it could potentially reduce the overall size and cost of the PT facilities. However, the laser-accelerated beams exhibit different characteristics than conventionally accelerated beams, i.e. very intense proton bunches with large divergences and broad-energy spectra. For the application of laser-driven beams in PT, new solutions for beam transport, such as beam capture, integrated energy selection, beam shaping and delivery systems are required due to the specific beam parameters. The generation of these beams are limited by the low repetition rate of high-power lasers and this limitation would require alternative solutions for tumour irradiation which can efficiently utilize the available high proton fluence and broad-energy spectra per proton bunch to keep treatment times short. This demands new dose delivery system and irradiation field formation schemes. In this paper, we present a multi-functional light-weight and compact proton gantry design for laser-driven sources based on iron-less pulsed high-field magnets. This achromatic design includes improved beam capturing and energy selection systems, with a novel beam shaping and dose delivery system, so-called ELPIS. ELPIS system utilizes magnetic fields, instead of physical scatterers, for broadening the spot-size of broad-energetic beams while capable of simultaneously scanning them in lateral directions. To investigate the clinical feasibility of this gantry design, we conducted a treatment planning study with a 3D treatment planning system augmented for the pulsed beams with optimizable broad-energetic widths and selectable beam spot sizes. High quality treatment plans could be achieved with such unconventional beam parameters, deliverable via the presented gantry and ELPIS dose delivery system. The conventional PT gantries are huge and require large space for the gantry to rotate the beam around the patient, which could be reduced up to 4 times with the presented pulse powered gantry system. The further developments in the next generation petawatt laser systems and laser-targets are crucial to reach higher proton energies. However, if proton energies required for therapy applications are reached it could be possible in future to reduce the footprint of the PT facilities, without compromising on clinical standards.

Impact of Hydrogen Bonding on the Susceptibility of Peptides to Oxidation.

The tendency of peptides to be oxidized is intimately connected with their function and even their ability to exist in an oxidative environment. Here we report high-level theoretical studies that show that hydrogen bonding can alter the susceptibility of peptides to oxidation, with complexation to a hydrogen-bond acceptor facilitating oxidation, and vice versa, impacting the feasibility of a diverse range of biological processes. It can even provide an energetically viable mechanistic alternative to direct hydrogen-atom abstraction. We find that hydrogen bonding to representative reactive groups leads to a broad (≈400 kJ mol-1 ) spectrum of ionization energies in the case of model amide, thiol and phenol systems. While some of the oxidative processes at the extreme ends of the spectrum are energetically prohibitive, subtle environmental and solvent effects could potentially mitigate the situation, leading to a balance between hydrogen bonding and oxidative susceptibility.

Effect of ion polishing on corrosion resistance of the cladding of fuel elements from E110 alloy in the steam water environment

The method of modification of the outer surface of the cladding of fuel elements from E110 Zr alloy by means of irradiation with a radial beam of Ar+ ions with a broad energy spectrum is proposed. It is shown that the use of ion beam treatment at the final stage of the cladding production can improve the surface quality owing to removal of a large part of surface defects after mechanical polishing. The kinetics of the growth of oxide films on ion-beam-treated (cleaning or polishing by Ar+ ions) tubular Zr alloy specimens in a steam environment (350, 375, and 400°C up to 3000 h) was investigated. Monoclinic zirconia layer formation is found to occur on the specimen surface oxidized at 350°C in water and steam environments. Oxidation of the fragments of the alloy fuel-element cladding in steam under pressure contributes to the formation of a thicker and more friable oxide film in comparison with the oxidation in water.

Towards swift ion bunch acceleration by high-power laser pulses at the Centre for Advanced Laser Applications (CALA)

Laser-driven acceleration of ions has inspired novel applications, that can benefit from ion bunch properties different from conventionally (non-laser based) accelerated particle beams. Those differences range from extremely short bunch durations, broad energy spectra, large divergence angles and small source sizes to ultra-high ion bunch densities. So far, the main focus of research has been concentrating on the physics of the interaction of intense laser pulses with plasmas and the related mechanisms of ion acceleration. Now, the new Centre for Advanced Laser Applications (CALA) near Munich aims at pushing these ion bunches towards applications, including radiation therapy of tumors and the development of heavy ion bunches with solid-state-like density. These are needed for novel reaction mechanisms (‘fission-fusion’) to study the origin of heavy elements in the universe and to prepare for related studies at the upcoming EU-funded high-power laser facility ELI – Nuclear Physics in Bucharest.

Determination of Z coordinate from track width in MiniTPC

A gas-filled Time Projection Chamber and a radioactive neutron source were used to study recoil tracks produced by scattering of the multi-MeV neutrons on gas nuclei. Since the event readout is triggered by the first electron arrival, the initial time and position in the electron drift direction are unknown, leading to a translational uncertainty in this direction. By using the track width due to electron diffusion, the coordinate along the drift direction was determined. With a suitable width calibration at a known drift distance, it is found that width measurements of the track can provide useful information for establishing a well-defined gas fiducial volume for the interactions. The coordinate determination is also sufficiently precise that it can be used as a third parameter in kinematic reconstruction of the neutron collision, providing improved knowledge of the neutron collision process. Despite a wide range of track ionization levels resulting from the broad spectrum of neutron energies and varying angles of scatter, the coordinate determination is not sensitive to the track ionization.

Binding energy of self-interstitial atoms to grain boundaries: An experimental approach

The energies of formation and binding of self-interstitial atoms at grain boundaries in tungsten have been found out using the field evaporation phenomenon. The binding-energy distribution for interstitials at the high-angle GB of general type is characterized by a broad characteristic energy spectrum energy spectrum with a full width at half maximum of 1.98eV. Our experimental results are compared with published theoretical data on the interaction of interstitials with grain boundaries and found to be qualitatively reliable.

One-dimensional hydrodynamic model generating a turbulent cascade.

As a minimal mathematical model generating cascade analogous to that of the Navier-Stokes turbulence in the inertial range, we propose a one-dimensional partial-differential-equation model that conserves the integral of the squared vorticity analog (enstrophy) in the inviscid case. With a large-scale random forcing and small viscosity, we find numerically that the model exhibits the enstrophy cascade, the broad energy spectrum with a sizable correction to the dimensional-analysis prediction, peculiar intermittency, and self-similarity in the dynamical system structure.

The multicomponent doping of surface layers of materials under the influence of ion beams with a broad energy spectrum

The paper discusses the various factors that influence the efficiency of ion mixing. It was found that in the base of penetration of atoms multilayer films in polycrystalline substrate is the process of energy transfer from ions and primary knocked-on atom (PKA) of films to subsequent displacement cascade. At the same time the penetration of implanted atoms to great depths determined by the density of defects, radiation-stimulated migration of interstitial atoms and their physico-chemical interaction with the atoms of the matrix, which can be described by the model of an isotropic mixing. It is shown that doping atoms of the multilayer films, possibly the formation of gradient layers, which are determined by radiation traces in the substrate implanted atoms and their migration under irradiation by the ion beam with a broad energy spectrum.