Tungsten Target Research Articles

Simulation of channeling radiation and positron production in thick diamond structures and a tungsten single crystal

The process of de-channeling for electrons of energy 2 GeV channeled in the (110) plane of silicon and tungsten single crystals has been studied. The dynamics of the particle distribution density has been investigated in dependence on both the energy and scattering distribution of the initial electron beam. The influence of de-channeling on the spectral intensity of channeling radiation has been investigated by solving the Fokker-Planck equation. A non-conventional positron source is described based on the generation of radiation by relativistic electrons channeled along different crystallographic planes or axes of W, Si, Ge and C (diamond) single crystals and the subsequent conversion of the radiation into e+e−-pairs in an amorphous tungsten target. The simulation of channeling radiation and its dependence on the incidence angle into the crystal has been carried out by means of our Mathematica codes. The conversion of the radiation into e+e−-pairs and the energy distribution of positrons have been simulated using the GEANT4 package.

Dynamics of prompt electrons, ions, and neutrals of nanosecond laser ablation of tungsten investigated using optical emission

A Nd:YAG laser with a power density of 15 GW/cm2, operating at a wavelength of 1064 nm, was used to ablate a tungsten (W) target placed in an ambient atmosphere of air at a pressure of 10 mbar. A systematic study of plasma properties employing fast photography and time and space resolved optical emission spectroscopy was carried out. The results showed that there were continuum, neutral, and singly ionized W atom optical emission in the laser-induced plasma; the spectra of ambient gas N2 and N2+ were aslo observed which appeared at very early times (<30 ns). The spectra of N2+ presented a temporal profile with a narrow width (∼20 ns) and a steep rising edge (∼10 ns) that was very close to the laser pulse duration, which revealed that the prompt electrons ejected from the W target collisionally excited and ionized ambient N2 gas molecules. The approximate timescales from nanoseconds to microseconds of four laser-produced W plasma processes including prompt electrons, continuum radiation, ions, and neutral emission were given according to time-resolved optical emission spectroscopy. Fast imaging showed that the prompt electrons were expanding hemispherically. The optical time of flight dynamics of N2+ corresponding to the prompt electrons at different positions showed that the kinetic energy of prompt electrons was up to 22 eV. These prompt electrons with high energy result in the separation from the core plasma which indicated the existence of the transient dynamic plasma sheath during the laser ablation process and interpreted the acceleration of ions.

Энерговыделение при бомбардировке атомами дейтерия поверхности вольфрама

The distribution of energy release (linear energy loss) over depth was calculated when bombarded with deuterium atoms of a tungsten target in a wide energy range of incident particles of 100 eV - 10 MeV. It is shown that in the energy range up to 100 keV, the maximum energy release, contrary to the prevailing ideas, is near the surface of a solid. At energies above 100 keV, the nature of the distribution changes and the Bragg maximum appears near the point where the particle stops. The distribution of the energy release over depth in tungsten is obtained for conditions typical of the ITER tokamak reactor, which makes it possible to estimate the wall heating during bombardment by plasma atoms.

An All-Solid-State Electrochromic Device Based on WO3–Nb2O5 Composite Films Prepared by Fast-Alternating Bipolar-Pulsed Reactive Magnetron Sputtering

In this study, WO3–Nb2O5 electrochromic films and an ITO/WO3–Nb2O5/Nb2O5/NiVOx/ITO all-solid-state electrochromic device were deposited using fast-alternating bipolar-pulsed magnetron sputtering using tungsten and niobium targets. The influence of different sputtering powers from the niobium target on the refractive index, extinction coefficient, optical modulation, coloration efficiency, reversibility, and durability of the WO3–Nb2O5 films is discussed. The aim of this work is to find the suitable Nb proportion to increase durability and less negative effect in the electrochromic performance of Nb2O5-doped WO3 films. The lifetime of the WO3–Nb2O5 films is 4 times longer than pure WO3 films when the sputtering power of the Nb target is higher than 250 W. The results show that WO3–Nb2O5 composite films used for an all-solid-state electrochromic device can sustain over 3 × 104 repeated coloring and bleaching cycles while the transmission modulations can be kept above 20%. The coloring and bleaching response times are 7.0 and 0.7 s, respectively.

Evaluation of tungsten influx rate and study of edge tungsten behavior based on the observation of EUV line emissions from W6+ ions in HL-2A

The tungsten spectrum in the extreme ultraviolet (EUV) wavelength range has been investigated in tokamak HL-2A to find line emissions from low-ionized tungsten ions which can be used for tungsten transport study in the plasma edge. For this purpose, tungsten is injected in the HL-2A plasma using the laser blow-off (LBO) technique with a newly developed double-layer tungsten target. The total number of injected tungsten particles can be accurately controlled by adjusting the distance from the focal lens to the tungsten target. A quasi-continuum spectrum called an unresolved transition array (UTA), consisting of many line emissions from several ionization stages of tungsten ions, is observed at around 50 Å as a typical indication of the tungsten spectrum. In the present HL-2A experiment the quasi-continuum of tungsten is mainly composed of line emissions from W14+ to W23+ ions. Analyzing the observed tungsten spectrum, two isolated line emissions of W VII (5p–5d: 216.219 Å) and W VII (5p–5d: 261.387 Å) from W6+ ions are successfully identified for the first time in tokamaks. The intensity ratio and the wavelengths of the two lines determined in the present experiment show good agreement with the intensity ratio calculated with a collisional-radiative model developed for the W6+ ion and a previous result by Sugar and Kaufman (1975 Phys. Rev. A 12 994), respectively. On the other hand, the W VII line emission occasionally reappears after the LBO injection, suggesting a re-entry of the tungsten deposited onto divertor plates and a movement of the strike point during the discharge to a certain area of the divertor plate where tungsten is deposited. Based on the W VII emission observed during the re-entry event of tungsten ions, an influx of the W6+ ion, , to the edge plasma is evaluated using the inverse photon efficiency calculated with the ADAS code and using an average-configuration option. As a result, it is found that is typically within the range (0.1–2.0) × 1013 cm−2 s−1. A brief discussion is also made on the influx evaluated in the present study.

The SHiP Experiment: Search for New Physics in the Neutrino Sector

The SHiP experiment (for Search for Hidden Particles) which will operate at the CERN Super Proton Synchrotron (SPS) is one of the most promising projects in the field of particle physics. The SPS 400-GeV/c proton beam will be dumped onto the molybdenum–tungsten target of the SHiP detector, and the data corresponding to 2 × 1020 protons on the target will be accumulated in five years of running. The experiment is aimed at a search for very weakly interacting neutral particles beyond the Standard Model framework referred to as novel physics particles: massive neutral leptons, axions, and “dark” photons. Possible existence of such particles can help explain such firmly established phenomena as the baryon asymmetry of the Universe, nonzero neutrino masses, and the presence of dark matter. Beyond that, the experimental program envisages extensive studies in neutrino physics. In particular, we aim at directly detecting the tau antineutrino—the only Standard Model particle which until now has escaped experimental detection. The envisaged search for the right-handed neutrino partners is particularly interesting: theoretically, their existence can help explain some observed phenomena not predicted by the Standard Model. Experimental investigations in the fields of tau-neutrino interactions (as the least studied sector of neutrino physics) and production of charmed particles and a search for interactions of particles of light dark matter will be carried out with a neutrino detector based on relativistic nuclear emulsion. The τ- and τ+ production events will be discriminated (whereby the production of tau antineutrinos will be directly detected) using special magnets developed for the SHiP emulsion detector. Presently, a prototype of the emulsion detector as a key element of the SHiP neutrino detector is being simulated, constructed, and tested. The nuclear-emulsion technology provides a record-high spatial resolution as required for detecting charged particles with extremely short lifetimes. The nuclear-emulsion data will be processed with the advanced automatic equipment available at the participating laboratories. Efficient scanning of large areas on nuclear emulsion relies on modern scanning equipment such as the PAVICOM measuring complex developed at the Lebedev Physical Institute. Thereby, one can efficiently process the data collected with any track detectors, including those irradiated by accelerator beams. On the whole, the construction of the SHiP detector poses a number of nontrivial physical and technical problems addressed by physicists from 62 laboratories operating in 16 countries.

Spallation Yield of Neutrons Produced in Tungsten and Bismuth Target Bombarded with 0.1 to 3 GeV Proton Beam

In this paper, we investigated a system, is composed of a natural tungsten and bismuth cylindrical targets. The target has been optimized to produce the maximum of neutrons yield with a diameter of 20 cm and varying height from 10 to 80 cm. The target is bombarded with a high-intensity accelerator by a 0.1 to 3 GeV proton beam. The protons are assumed uniformly distributed across the beam of diameter 2 cm. In this work, we have used Monte Carlo method by using MCNP-6 code to simulate spallation neutron yield, neutron spectrum and distribution of the spallation neutrons coming out of the target in the target region. According to the results approving using several simulations for two targets tungsten and bismuth, the difference of spallation neutron yield increases by 8.92% using a bismuth target and for some beam energy 3 GeV.

Deep Ultraviolet Emitting Scintillators for Biomedical Applications: The Hard Way of Downsizing LuPO4:Pr3+

AbstractPr3+‐doped LuPO4 emits UV radiation between 225 and 280 nm, where DNA shows strong absorption bands. Therefore, a systematic study of the luminescence of Pr3+ doped LuPO4 is performed: Different doping concentrations, particles sizes, and excitation schemes (vacuum UV at 160 nm and X‐rays 50 kV, 2 mA, tungsten target) are compared. The emission spectra in the UV range depends on the excitation energy and the particle size. Microcrystalline particles (6 µm) comprising 1% Pr3+ display the highest emission intensity at 234 nm upon vacuum UV as well as X‐ray excitation. Sub‐microscale particles (20–50 nm) of LuPO4:Pr3+ (1%) show the same UV emission under X‐ray excitation as the larger particles but do not emit under vacuum UV excitation. Colloidal nanoscale particles (5 nm) do not show emission in the UV‐C range. Based on the high‐density and strong X‐ray absorption of LuPO4, the implementation of Pr3+ doped LuPO4 particles of suitable size (20–50 nm) could improve the well‐established radiation therapy. Owing to the strong absorption and low penetration depth of UV‐C radiation in biological tissue, Pr3+‐doped LuPO4 particles located directly in cancerous tumors could allow for additional treatment with cell‐damaging UV‐C radiation.

Usability Evaluation of a New Elastic Immobilization with Metal Markers for Image-Guided Radiation Therapy for Breast Cancer

We developed an elastic immobilization based on a commercially available brassier for postoperative radiotherapy for breast cancer. The purpose of this study was to validate the positioning accuracy and the surface doses of image-guided radiotherapy (IGRT) for breast cancer using the immobilization. The elastic immobilization had six small metal markers. We developed the human phantom with a tungsten target in the breast, which had an equivalent form and flexibility to soft tissues of the human body. First, the positioning accuracy of IGRT was evaluated using onboard imaging devices. The immobilization was fixed on the human phantom; the landmarks were drawn on the phantom to indicate positional relationship between the immobilization and body. The setup of the phantom was performed five times, and then several x-ray images were produced. The position verification was performed using the metal markers of the immobilization. The margin of a breast target was estimated using the expanded uncertainty calculated from the displacement between simulated and measured the tungsten target positions. The expanded uncertainty value was obtained by multiplying the combined standard uncertainty value by a coverage factor (k = 2; confidence interval, 95%). Next, the surface doses were measured using the thermoluminescent dosimeters with kV planar imaging at 80 kVp / 100 kVp, 5 mAs, and cone beam computed tomography (CBCT) at 120 kVp, 180 mAs. The measured doses with and without the immobilization were compared. Finally, they were compared with the calculated dose using the EGSnrc Monte Carlo code under the same conditions. The displacement of the tungsten target was 2.31 ± 0.53 mm, -1.21 ± 1.90 mm and -0.11 ± 0.67 mm in the lateral, longitudinal and vertical directions, respectively. The three-dimensional translation vector of variation was 3.28 ± 0.59 mm. The accuracy of IGRT with the elastic immobilization was 3.30 ± 0.53 mm (k = 2). The measured surface doses with and without the immobilization were 0.53 ± 0.28 mGy and 0.97 ± 0.19 mGy in kV planar image pair, 5.50 ± 1.40 mGy and 5.90 ± 1.45 mGy in CBCT, respectively. Similarly, the calculated dose was decreased by using immobilization in CBCT. This study showed a new elastic immobilization with the metal markers could provide positioning accuracy of IGRT for breast cancer with minimum skin markers. Furthermore, the immobilization decreased the surface doses of IGRT.Abstract TU_26_3153; Table 1Uncertainty budget of tungsten target position in IGRT with elastic immobilization (mm).Source of uncertaintyValue (±)Probability distributionDivided factorStandard uncertaintyu1: x-ray correction0.59normal10.26u2: imager position0.12normal10.01uc: combinednormal0.27U: expanded (k = 2)normal0.53 Open table in a new tab

Impact of heat treatment on tensile properties of 97W[sbnd]2Ni[sbnd]1Fe heavy alloy

To avoid failures caused by the inherent brittleness of pure tungsten below its ductile to brittle transition temperature, tungsten heavy alloy was proposed as an alternative solution of the plasma facing material. Plasma facing components manufactured of tungsten heavy alloy have been installed partly in the tokamak ASDEX Upgrade instead of pure tungsten targets. Opposite to the pure tungsten targets, no deep cracks have been identified in these targets after one experimental campaign. In order to understand and improve the material behavior of tungsten heavy alloy as plasmam facing material in ASDEX Upgrade, the impact of heat treatment on tensile properties of 97W2Ni1Fe heavy alloy has been studied in this work. The heat treatments have been conducted in the vacuum for the tensile specimen cut from an ASDEX Upgrade target at different temperatures (600 °C, 1100 °C and 1350 °C) with various durations (15 min, 60 min and 120 min). After the heat treatment, the tensile properties were remarkably improved. The increase of the interfacial strength between tungsten grains and matrix phase as well as growth of grains are considered as the main reasons for the increase of elongation after heat treatment. The experimental results reveal that electrical discharge machining reduces the total elongation of the specimens. Furthermore, no big impact on the tensile properties is found after low energy deuterium plasma implantation.

Multiplication characteristics of a gas-cooled ADS with fast-thermal coupling configuration

Abstract The Accelerator Driven Subcritical Reactor System (ADS) is developed to transmute the nuclear wastes. Nevertheless, just like the traditional reactors, the ADS is faced with the problem of how to remove the decay heat efficiently. In order to solve the problem, a design of helium-cooled ADS with tungsten target is presented in this paper, and the multiplication characteristics of it are researched. The design of the subcritical core is based on the scheme of high temperature gas-cooled reactor, and to improve the ability of transmutation, the subcritical core is divided into two regions, which form up the fast-thermal coupling configuration. The parameters of fuel arrangement, position of target, height of active core, and height of top/bottom reflector are optimized to achieve the good physical and thermal performance. In the process of optimization, the influences of these parameters on the characteristics of the core are investigated through numerical experiments simulated by the MCNP6 code. The results indicate that the K eff and the K s may differ considerably for the gas-cooled ADS with fast-thermal coupling configuration. Moreover, we find that even with the same K eff , the K s of the subcritical core is different for similar schemes.

UV-visible light-induced antibacterial and photocatalytic activity of half harmonic generator WO3 nanoparticles synthesized by Pulsed Laser Ablation in water

In this study, synthesis of WO3 nanoparticles (NPs), using the physically clean method known as laser ablation of a tungsten target immersed in distilled water is reported. Fundamental wavelength of an acousto-optically Q-switched Nd:YAG laser with 13, 18, 23 J/cm2 laser fluences was utilized for this purpose. Transmission Electron Microscopy (TEM) associated with Dynamic Light Scattering (DLS) show an increase in average particle size as the laser fluence increases from 13 to 23 J/cm2, also with a precise look into the TEM images, the chains of WO3 NPs are observable although the length of the chains decreases while decreasing the laser fluence. Photocatalytic and antimicrobial activity of the products against E. coli (Escherichia coli) bacteria under UV and visible light illumination were investigated and showed that for photocatalytic and antibacterial processes, active surface area and energy band gap play the main roles while illuminating the nanoparticle samples with UV and visible light, respectively. Moreover, anti-UV properties of the products originated from half harmonic generation process were corroborated by PL (photoluminescence) emission studies.

Stationary Computed Tomography for Space and other Resource-constrained Environments

Computed tomography (CT) is used to diagnose many emergent medical conditions, including stroke and traumatic brain injuries. Unfortunately, the size, weight, and expense of CT systems make them largely inaccessible for patients outside of major hospitals. We have designed a module containing multiple miniature x-ray sources that could allow for CT systems to be significantly lighter, smaller, and cheaper, and to operate without any moving parts. We have developed a novel photocathode-based x-ray source, created by depositing a thin film of magnesium on an electron multiplier. When illuminated by a UV LED, this photocathode emits a beam of electrons, with a beam current of up to 1 mA. The produced electrons are accelerated through a high voltage to a tungsten target. These sources are individually addressable and can be pulsed rapidly, through electronic control of the LEDs. Seven of these sources are housed together in a 17.5 degree arc within a custom vacuum manifold. A full ring of these modules could be used for CT imaging. By pulsing the sources in series, we are able to demonstrate x-ray tomosynthesis without any moving parts. With a clinical flat-panel detector, we demonstrate 3D acquisition and reconstructions of a cadaver swine lung.

Tungsten Target Optimization for Photon Fluence Maximization of a Transmission-Type Flat-Panel X-Ray Source by Monte Carlo Simulation and Experimental Measurement

The cold cathode flat-panel X-ray source is a new type of X-ray source with advantage of smaller footprint and lower-dose imaging than current sources. In this paper, we optimized the thickness of the anode target of a flat-panel X-ray source to maximize the photon fluence of X-rays generated from the device. Utilizing EGSnrc-based Monte Carlo code, X-ray fluence was calculate from the simulated photons deposited in the virtual detector. These results revealed an optimal target thickness at a specific anode voltage to maximize the output of X-ray intensity. For experimental validation, tungsten thin film anodes with different thicknesses were prepared, and a flat-panel X-ray source was fabricated using a ZnO nanowire cold cathode. A figure of merit was introduced to characterize the output efficiency of the X-rays. The experimental results agree well with the simulation results, showing an optimal tungsten-target thickness of 1200 nm at an anode voltage of 40 kV. Using a flat-panel X-ray source with the optimized anode thickness, we took X-ray absorption images of both biological and nonbiological subjects, and high-resolution images were demonstrated.

Fast High-Energy X-Ray Imaging for Severe Accidents Experiments on the Future PLINIUS-2 Platform

The future PLINIUS-2 platform of the Commissariat a l’Energie Atomique (CEA) of Cadarache will be dedicated to the study of corium interactions in severe nuclear accidents, and will host innovative large-scale experiments. The nuclear measurement laboratory of CEA Cadarache is in charge of real-time high-energy X-ray imaging setups, for the study of the corium–water and corium–sodium interaction, and of the corium stratification process. Imaging such large and high-density objects requires a 15 MeV linear electron accelerator coupled to a tungsten target creating a high-energy bremsstrahlung X-ray flux, with corresponding dose rate about 100 Gy/min at 1 m. The signal is detected by phosphor screens coupled to high-framerate scientific CMOS cameras. The imaging setup is established using an experimentally validated home-made simulation software High-Energy MODeling for RAdiography and TOmography (MODHERATO). The code computes quantitative radiographic signals from the description of the source, object geometry and composition, detector, and geometrical configuration (magnification factor, etc.). It accounts for several noise sources (photonic and electronic noises, and swank and readout noise), and for image blur due to the source spot-size and to the detector unsharpness. In a view to PLINIUS-2, the simulation has been improved to account for the scattered flux, which is expected to be significant. This paper presents the scattered flux calculation using the Monte-Carlo N-particle transport code, and its integration into the MODHERATO simulation. Then, the validation of the improved simulation is presented, through confrontation to real measurement images taken on a small-scale equivalent setup on the PLINIUS platform. Excellent agreement is achieved. This improved simulation is therefore being used to design the PLINIUS-2 imaging setups (source, detectors, and cameras). Simulation will be presented for different configurations, as well as preliminary tests of alternative detectors considered for PLINIUS-2.

The optimization on neutronic performance of the granular spallation target by using low-density porous tungsten

The concept of gravity-driven Dense Granular Target (DGT) has been proposed and tungsten granule is one of the candidate target materials. With the increase of DGT diameter, the source efficiency is significantly reduced, which is not conducive to the design of high-power. Low density porous tungsten particles are proposed as the target material of DGT instead of the natural tungsten. First, the neutronics of the bare target have been studied with porous tungsten granule density using Monte Carlo code. An ADS model was then set up to evaluate the neutron sources performance caused by density variation of porous tungsten granule. The results show that there is an optimal combination of tungsten granular density and target diameter to make the utmost of leakage neutrons. In the ADS driven by tungsten DGT, an appropriate density porous tungsten as the target material can effectively increase the source efficiency, reduce the beam requirement and the thermal deposition on the target.

Measurement and calculation of decay heat in ISIS spallation neutron target

Thermal powers from radioactive decays (‘decay heat’) within a proton-driven neutron-producing tungsten target on the ISIS Spallation Neutron Source have been measured. Very good agreement is found with calculations using the Monte Carlo code MCNPX.

Neutron transport and benchmark on granular tungsten samples with 14.8 MeV neutrons

The leakage neutron spectrum from granular tungsten samples was measured by a TOF technique at 60°. The neutron transport and benchmark on granular tungsten samples were investigated using MCNP-4C simulations with the ENDF/B-VII.1, CENDL-3.1, JEFF-3.2, JENDL-4.0 and TENDL-2015 evaluated nuclear data libraries. And four different geometry lattices (FCC, BCC, CHPOP and SC) were considered for the granular tungsten target. The simulated results show that the leakage neutron spectrum mainly depends on the filling factor of granular tungsten. The general trend of the experimental leakage neutron spectrum is well reproduced by MCNP simulation with the ENDF/B-VII.1 library within 15% error. However, the inelastic contribution at around En = 10 MeV with CENDL-3.1 library largely underestimates the cross section. The discrepancies of the leakage neutron spectra in the MCNP simulations originate simply from the differences in the spectra distributions of the neutron reaction channels in the evaluated nuclear data libraries.

Possible atmospheric-like neutron beams at CSNS

The China Spallation Neutron Source (CSNS) has started commissioning in early 2018. The neutron spectrum from the tungsten target bombarded by a 1.6 GeV proton beam is very wide, namely with characteristics of a white neutron spectrum. In this paper two white neutron beams schemed at CSNS are simulated by using the FLUKA code. And the beam spectrum and intensity are compared with that from other neutron sources in the world. The fidelity for the chip irradiation experiments by using the neutron spectra of these two white-neutron beam lines is estimated. These atmospheric-like neutron beams will be the first white neutron beam lines at CSNS and more intensive ones for carrying out an accelerated test of the neutron-induced single event effect (SEE) will be available in a few years.

Bright muon source driven by GeV electron beams from a compact laser wakefield accelerator

We report here a systematic quantitative study on the generation and characteristics of an active muon source driven by the interaction of an electron beam within the energy range of 1–10 GeV from laser wakefield acceleration (LWFA) with a tungsten target, using Monte Carlo simulations. The 10 GeV electron beam, achievable in the near future, from LWFA using femtosecond multi-PW lasers is employed to drive the bright source of muon pairs in a compact setup. We show that a highly directional and intense source of short-pulsed GeV muon pairs (μ−μ+) have a peak brightness of 5 × 1017 pairs s–1cm–2sr–1 and sub-100 ps duration could be produced using a quasi-monoenergetic 10 fs, 10 GeV electron bunch with a 1-mrad divergence and 100 pC charge. The muon pairs are emitted from a point-like source with a well-defined position and timing; the source has a size and geometric emittance of about 1 mm and 40 μm, respectively. Such muon sources can greatly benefit applications in muon radiography as well as studies on anomalous dipole moments, rare decays of muons, neutrino oscillations, and an injector for a future compact muon collider.