Bremsstrahlung X-ray Research Articles

A pulsed generator of X-ray bremsstrahlung with a high peak exposure rate

A new pulsed generator of X-ray bremsstrahlung based on an inductive energy storage and a plasma opening switch is described. The radiation parameters are as follows: the peak exposure rate is as high as 5 × 109 R/s, and the dose is as high as 800 R.

Laser-Optical and X-Ray Characterization of an Operating High-Voltage Piezoelectric Transformer in Multiple Vibrational Modes

A crystal of lithium niobate was configured for use as a longitudinal-mode piezoelectric transformer (PT). An electron gun was coupled to the transformer to allow for controlled release of charge to the high-voltage terminal of the PT. An electron tube extracted a beam from a thermionic emission source, and cylindrical optics focused the beam to a 2-mm spot at the PT output. Two diagnostic methods were used to measure the operation of the PT: bremsstrahlung X-ray spectroscopy and laser-optical interrogation. Both diagnostics showed that the PT is able to process up to 1.5 $\mu \text{A}$ of current at 20-kV output in a continuous mode. The laser-optical method was also used to compare the mechanical stress, electric field, and developed voltage between the fundamental and secondary harmonic resonance modes.

Development of Compton X-ray spectrometer for high energy resolution single-shot high-flux hard X-ray spectroscopy.

Hard X-ray spectroscopy is an essential diagnostics used to understand physical processes that take place in high energy density plasmas produced by intense laser-plasma interactions. A bundle of hard X-ray detectors, of which the responses have different energy thresholds, is used as a conventional single-shot spectrometer for high-flux (>10(13) photons/shot) hard X-rays. However, high energy resolution (Δhv/hv < 0.1) is not achievable with a differential energy threshold (DET) X-ray spectrometer because its energy resolution is limited by energy differences between the response thresholds. Experimental demonstration of a Compton X-ray spectrometer has already been performed for obtaining higher energy resolution than that of DET spectrometers. In this paper, we describe design details of the Compton X-ray spectrometer, especially dependence of energy resolution and absolute response on photon-electron converter design and its background reduction scheme, and also its application to the laser-plasma interaction experiment. The developed spectrometer was used for spectroscopy of bremsstrahlung X-rays generated by intense laser-plasma interactions using a 200 μm thickness SiO2 converter. The X-ray spectrum obtained with the Compton X-ray spectrometer is consistent with that obtained with a DET X-ray spectrometer, furthermore higher certainly of a spectral intensity is obtained with the Compton X-ray spectrometer than that with the DET X-ray spectrometer in the photon energy range above 5 MeV.

Vertical intensity modulation for improved radiographic penetration and reduced exclusion zone

In the present work, a method to direct the X-ray beam in real time to the desired locations in the cargo to increase penetration and reduce exclusion zone is presented. Cargo scanners employ high energy X-rays to produce radiographic images of the cargo. Most new scanners employ dual-energy to produce, in addition to attenuation maps, atomic number information in order to facilitate the detection of contraband. The electron beam producing the bremsstrahlung X-ray beam is usually directed approximately to the center of the container, concentrating the highest X-ray intensity to that area. Other parts of the container are exposed to lower radiation levels due to the large drop-off of the bremsstrahlung radiation intensity as a function of angle, especially for high energies (&gt;6 MV). This results in lower penetration in these areas, requiring higher power sources that increase the dose and exclusion zone. The capability to modulate the X-ray source intensity on a pulse-by-pulse basis to deliver only as much radiation as required to the cargo has been reported previously. This method is, however, controlled by the most attenuating part of the inspected slice, resulting in excessive radiation to other areas of the cargo. A method to direct a dual-energy beam has been developed to provide a more precisely controlled level of required radiation to highly attenuating areas. The present method is based on steering the dual-energy electron beam using magnetic components on a pulse-to-pulse basis to a fixed location on the X-ray production target, but incident at different angles so as to direct the maximum intensity of the produced bremsstrahlung to the desired locations. The details of the technique and subsystem and simulation results are presented.

A laser driven pulsed X-ray backscatter technique for enhanced penetrative imaging.

X-ray backscatter imaging can be used for a wide range of imaging applications, in particular for industrial inspection and portal security. Currently, the application of this imaging technique to the detection of landmines is limited due to the surrounding sand or soil strongly attenuating the 10s to 100s of keV X-rays required for backscatter imaging. Here, we introduce a new approach involving a 140 MeV short-pulse (< 100 fs) electron beam generated by laser wakefield acceleration to probe the sample, which produces Bremsstrahlung X-rays within the sample enabling greater depths to be imaged. A variety of detector and scintillator configurations are examined, with the best time response seen from an absorptive coated BaF2 scintillator with a bandpass filter to remove the slow scintillation emission components. An X-ray backscatter image of an array of different density and atomic number items is demonstrated. The use of a compact laser wakefield accelerator to generate the electron source, combined with the rapid development of more compact, efficient and higher repetition rate high power laser systems will make this system feasible for applications in the field. Content includes material subject to Dstl (c) Crown copyright (2014). Licensed under the terms of the Open Government Licence except where otherwise stated. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@ nationalarchives.gsi.gov.uk.

Transmission type flat-panel X-ray source using ZnO nanowire field emitters

A transmission type flat-panel X-ray source in diode structure was fabricated. Large-scale patterned ZnO nanowires grown on a glass substrate by thermal oxidation were utilized as field emitters, and tungsten thin film coated on silica glass was used as the transmission anode. Uniform distribution of X-ray generation was achieved, which benefited from the uniform electron emission from ZnO nanowires. Self-ballasting effect induced by the intrinsic resistance of ZnO nanowire and decreasing of screening effect caused by patterned emitters account for the uniform emission. Characteristic X-ray peaks of W-L lines and bremsstrahlung X-rays have been observed under anode voltages at a range of 18–20 kV, the latter of which were the dominant X-ray signals. High-resolution X-ray images with spatial resolution less than 25 μm were obtained by the flat-panel X-ray source. The high resolution was attributed to the small divergence angle of the emitted X-rays from the transmission X-ray source.

Dynamics of the microstructure of current channels and the generation of high-energy electrons in nanosecond discharges in air

The results of the three-dimensional numerical simulation of the dynamics of the microstructure of high-voltage nanosecond discharges in air at atmospheric pressure are presented. It is established that the fast (at a time of ≈10 ns) broadening and significant decrease in the gas concentration in the microchannels occur as a result of the ohmic heating of microchannels with the diameter of 1–30 μm. It was shown that the broadening of microchannels in a nanosecond diffusive discharge provides an increase in the ratio of the electric field strength to the gas concentration in microchannels to values sufficient for the generation highenergy electron beams and X-ray bremsstrahlung in them. Features of the dynamics of the system of microchannels and its effect on the efficiency of the generation of high-energy electrons in discharges developing in the microstructuring regime of the current channels are considered.

High-Energy X-Ray Imaging Applied to Nondestructive Characterization of Large Nuclear Waste Drums

As part of its R&D programs on non-destructive testing of nuclear waste drums, CEA is commissioning an irradiation cell named CINPHONIE, at Cadarache. This cell allows high-energy imaging (radiography and tomography) on large volumes (up to $5 ~\hbox{m}^3$ ) and heavy weights (up to 5 tons). A demonstrator has been finalized, based on existing components. The X-ray source is a 9 MeV LINAC which produces Bremsstrahlung X-rays (up to 23 Gy/min at 1 meter in the beam axis). The mechanical bench is digitally controlled on three axes (translation, rotation, elevation) and can handle objects up to 2 t. This bench performs trajectories necessary for acquisition of projections (sinograms) according to different geometries: Translation-Rotation, Fan-Beam and Cone-Beam. Two detection systems both developed by CEA-Leti are available. The first one is a large GADOX scintillating screen ( $800 \times 600~\hbox{mm}^{2}$ ) coupled to a low-noise pixelated camera. The second one is a multi-CdTe semiconductor detector, offering measurements up to 5 decades of attenuation (equivalent to 25 cm of lead or 180 cm of standard concrete). At the end of the acquisition, a Filtered Back Projection-based algorithm is performed. Then, a density slice (fan-beam tomography) or a density volume (cone-beam tomography or helical tomography) is produced and used to examine the waste. Characterization of LINAC, associated detectors as well as the full acquisition chain, are presented. Experimental performances on phantoms and real drum are discussed and expected limits on defect detectability are evaluated by simulation. The final system, designed to handle objects up to 5 tons is then presented.

High-temperature differential emission measure and altitude variations in the temperature and density of solar flare coronal X-ray sources

The detailed knowledge of plasma heating and acceleration region properties presents a major observational challenge in solar flare physics. Using the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the high temperature differential emission measure, DEM(T), and the energy-dependent spatial structure of solar flare coronal sources are studied quantitatively. The altitude of the coronal X-ray source is observed to increase with energy by ~+0.2 arcsec/keV between 10 and 25 keV. Although an isothermal model can fit the thermal X-ray spectrum observed by RHESSI, such a model cannot account for the changes in altitude, and multi-thermal coronal sources are required where the temperature increases with altitude. For the first time, we show how RHESSI imaging information can be used to constrain the DEM(T) of a flaring plasma. We develop a thermal bremsstrahlung X-ray emission model with inhomogeneous temperature and density distributions to simultaneously reproduce: i) DEM(T), ii) altitude as a function of energy, and iii) vertical extent of the flaring coronal source versus energy. We find that the temperature-altitude gradient in the region is ~+0.08 keV/arcsec (~1.3 MK/Mm). Similar altitude-energy trends in other flares suggest that the majority of coronal X-ray sources are multi-thermal and have strong vertical temperature and density gradients with a broad DEM(T).

Photoelectron emission from metal surfaces induced by radiation emitted by a 14 GHz electron cyclotron resonance ion source.

Photoelectron emission measurements have been performed using a room-temperature 14 GHz ECR ion source. It is shown that the photoelectron emission from Al, Cu, and stainless steel (SAE 304) surfaces, which are common plasma chamber materials, is predominantly caused by radiation emitted from plasma with energies between 8 eV and 1 keV. Characteristic X-ray emission and bremsstrahlung from plasma have a negligible contribution to the photoelectron emission. It is estimated from the measured data that the maximum conceivable photoelectron flux from plasma chamber walls is on the order of 10% of the estimated total electron losses from the plasma.

Spectrum for nonmagnetic mott insulators from power functional within reduced density matrix functional theory.

We demonstrate that reduced density matrix functional theory (RDMFT), in conjunction with the power functional, can successfully treat the nonmagnetic insulating state of the transition metal oxides NiO and MnO, finding for both a gapped single particle spectrum. While long-range spin order is thus not necessary for qualitative agreement with experiment, we find that it is required for good agreement with the X-ray photoemission spectroscopy and Bremsstrahlung isochromat spectroscopy data. We further examine the nature of the natural orbitals in the materials, finding that they display significant Hubbard localization and are, as a consequence, very far from the corresponding Kohn-Sham orbitals. This contrasts with the case of the band insulator Si, in which the Kohn-Sham orbitals are found to be very close to the RDMFT natural orbitals.

Characterization of intense laser-produced fast electrons using hard x-rays via bremsstrahlung

Energy distribution of high-power, short-pulse laser produced fast electrons was experimentally and numerically studied using high-energy bremsstrahlung x-rays. The hard x-ray photons and escaping electrons from various metal foils, irradiated by the 50 TW Leopard laser at Nevada Terawatt Facility, were recorded with a differential filter stack spectrometer that is sensitive to photons produced by mainly 0.5–2 MeV electrons and an electron spectrometer measuring >2 MeV electrons. The experimental bremsstrahlung and the slope of the measured escaped electrons were compared with an analytic calculation using an input electron spectrum estimated with the ponderomotive scaling. The result shows that the electron spectrum entering a Cu foil could be continuous single slope with the slope temperature of ∼1.5 MeV in the detector range. The experiment and analytic calculation were then compared with a 2D particle-in-cell code, PICLS, including a newly developed radiation transport module. The simulation shows that a two-temperature electron distribution is generated at the laser interaction region, but only the hot component of the fast electrons flow into the target during the interaction because the low energy electron component is trapped by self-generated magnetic field in the preformed plasma. A significant amount of the photons less than 100 keV observed in the experiment could be attributed to the low energy electrons entering the foil a few picoseconds later after the gating field disappears.

Ag K-shell ionization by electron impact: New cross-section measurements between 50 and 100keV and review of previous experimental data

Abstract We report the measurement of Ag K-shell ionization cross-section by electron impact in the range 50–100 keV and review the experimental data found in the literature. The sample consisted in a thin film of Ag evaporated on a thin C backing. The x-ray spectra generated by electron bombardment in the Sao Paulo Microtron were observed with a planar HPGe detector. The ratios between characteristic and bremsstrahlung x-ray yields were transformed to ionization cross sections with the help of theoretical atomic-field bremsstrahlung cross sections. The measured cross sections are compared with existing experimental values and calculations based on the semi-relativistic distorted-wave Born approximation. According to our experiment, the ratio of Ag K β to K α x-ray intensities is 0.2018(24).

The Spectrometer/Telescope for Imaging X-rays on Solar Orbiter: Flight design, challenges and trade-offs

STIX is the X-ray spectral imaging instrument on-board the Solar Orbiter space mission of the European Space Agency, and together with nine other instruments will address questions of the interaction between the Sun and the heliosphere. STIX will study the properties of thermal and accelerated electrons near the Sun through their Bremsstrahlung X-ray emission, addressing in particular the emission from flaring regions on the Sun. The design phase of STIX has been concluded. This paper reports the final flight design of the instrument, focusing on design challenges that were faced recently and how they were addressed.

ROSAT x-ray analysis of the AM Her cataclysmic variable VV Pup

VV Pup is typical system of AM Her stars, where the main accreting pole rotates in and out of view during the orbital cycle. In the present paper we present ROSAT data analysis for the magnetic cataclysmic variable VV Pup. We obtained the X-ray light curves of VV Pup in high state, the PSPC count rate 0.1-2.0 keV is plotted as a function of time with bins of 10 sec and the count rate is folded over the orbital period of 100.4 min with bin size of 100 sec for individual observations. We calculate the mean best-fit PSPC spectrum, with a three-component spectral fit including a soft X-ray blackbody, hard X-ray bremsstrahlung, and Gaussian line covers the phase intervals, for a bright phase (phi_orb=0.9-1.1), the dip data (phi_orb=0.18-0.7), the egress from the dip (phi_orb=0.7-0.8), the phase interval phi = 0.1-0.18 and the mean best-fit spectrum for all data (phi_orb=0.0-1.0). We calculate spectral parameters, the hardness ratios, count rate and total integrated black body flux.

Global-scale coherence modulation of radiation-belt electron loss from plasmaspheric hiss.

Over 40 years ago it was suggested that electron loss in the region of the radiation belts that overlaps with the region of high plasma density called the plasmasphere, within four to five Earth radii, arises largely from interaction with an electromagnetic plasma wave called plasmaspheric hiss. This interaction strongly influences the evolution of the radiation belts during a geomagnetic storm, and over the course of many hours to days helps to return the radiation-belt structure to its 'quiet' pre-storm configuration. Observations have shown that the long-term electron-loss rate is consistent with this theory but the temporal and spatial dynamics of the loss process remain to be directly verified. Here we report simultaneous measurements of structured radiation-belt electron losses and the hiss phenomenon that causes the losses. Losses were observed in the form of bremsstrahlung X-rays generated by hiss-scattered electrons colliding with the Earth's atmosphere after removal from the radiation belts. Our results show that changes of up to an order of magnitude in the dynamics of electron loss arising from hiss occur on timescales as short as one to twenty minutes, in association with modulations in plasma density and magnetic field. Furthermore, these loss dynamics are coherent with hiss dynamics on spatial scales comparable to the size of the plasmasphere. This nearly global-scale coherence was not predicted and may affect the short-term evolution of the radiation belts during active times.

Radiation Testing of the GERD Stimulation Therapy System Using a Particle Accelerator.

This testing was conducted to determine if exposure from a particle accelerator used to treat cancer patients would alter the performance of the EndoStim® neurostimulator when programmed either passively or actively and while being irradiated. A total of 12 EndoStim Lower Esophageal Sphincter (LES) Stimulation System implantable neurostimulators were investigated in this research. Included were six each of the EndoStim I and EndoStim II. Half were used for passive testing, with the remaining half for active testing. Bremsstrahlung x-rays were delivered having a nominal energy of 18 MV at a rate of 6 Gy/min. A total dose of 80 Gy was achieved in testing minimally. Monitoring of stimulation frequency, amplitude, pulse width, stimulation time, and voltage was conducted using software developed by EndoStim along with an oscilloscope. No observed changes to the intended stimulation were noted and all scheduled parameter magnitudes were achieved with device operation. All functional parameter changes were within ±10% from baseline. EndoStim I and EndoStim II implant pulse generators appear to be immune to x-ray radiation from the particle accelerator at energies up to 18 MV, at dose rates of up to 6 Gy/min, and up to cumulative doses of minimally 80 Gy. As there were no observable effects on neurostimulation requirements, the EndoStim LES Stimulation System implantable neurostimulators are capable of withstanding direct radiation. The recommendations of the manufacturer should be followed further regarding the labeling requirements for insured safety to patients.

Quasi-periodic oscillations in accreting magnetic white dwarfs

Quasi-periodic oscillations (QPOs) are observed in the optical flux of some polars with typical periods of 1 to 3 s but none have been observed yet in X-rays where a significant part of the accreting energy is released. QPOs are expected and predicted from shock oscillations. Most of the polars have been observed by the XMM-Newton satellite. We made use of the homogeneous set of observations of the polars by XMM-Newton to search for the presence of QPOs in the (0.5–10 keV) energy range and to set significant upper limits for the brightest X-ray polars. We extracted high time-resolution X-ray light curves by taking advantage of the 0.07 s resolution of the EPIC-PN camera. Among the 65 polars observed with XMM-Newton from 1998 to 2012, a sample of 24 sources was selected on the basis of their counting rate in the PN instrument to secure significant limits. We searched for QPOs using Fast Fourier Transform (FFT) methods and defined limits of detection using statistical tools. Among the sample surveyed, none shows QPOs at a significant level. Upper limits to the fractional flux in QPOs range from 7% to 71%. These negative results are compared to the detailed theoretical predictions of numerical simulations based on a 2D hydrodynamical code presented in Paper II. Cooling instabilities in the accretion column are expected to produce shock quasi-oscillations with a maximum amplitude reaching ~40% in the bremsstrahlung (0.5–10 keV) X-ray emission and ~20% in the optical cyclotron emission. The absence of X-ray QPOs imposes an upper limit of ~(5–10) g cm-2 s-1 on the specific accretion rate but this condition is found inconsistent with the value required to account for the amplitudes and frequencies of the observed optical QPOs. This contradiction outlines probable shortcomings with the shock instability model.

Investigation of Simultaneous Photons and Electrons Beam by Monte Carlo Code

Background:: Depending on the location and depth of tumor, the electron or photon beams might be used for treatment. Electron beam have some advantages over photon beam for treatment of shallow tumors to spare the normal tissues beyond of the tumor. In the other hand, the photon beam are used for deep targets treatment. Both of these beams have some limitations, for example, the dependency of penumbra with depth, and the lack of lateral equilibrium for small electron beam fields. Objectives:: In this study, improvement of the penumbra and Dmax changes will be investigated. Also the effects of cut-outs on the beam parameters prepared as well. Patients and Methods:: In first, we simulated the conventional head configuration of Varian 2300 for 16 MeV electron, and the results approved by benchmarking the percent depth dose (PDD) and profile of the simulation and measurement. In the next step, a perforated Lead (Pb) sheet with 1 mm thickness placed at the top of the applicator holder tray. This layer producing bremsstrahlung x-ray and a part of the electrons passing through the holes, in result, we have a simultaneous mixed electron and photon beam. For making the irradiation field uniform, a layer of steel placed after the Pb layer. The simulation was performed for 10 × 10, and 4 × 4 cm2 field size. Results:: The measured R50 and RP for 10 × 10 cm2 field were 6.5 and 7.8 cm, respectively. The photon percentage for 1 mm thickness with 0.2, 0.3, and 0.5 cm holes diameter Lead layer target was about 33%, 32%, and 28% and for 2 mm targets punched with 0.2, 0.3, and 0.5 cm holes, the x-ray percentages were 43%, 41%, and 35%. Conclusions:: This study showed the advantages of mixing the electron and photon beam by reduction of pure electron’s penumbra dependency with the depth, especially for small fields, also decreasing of dramatic changes of PDD curve with irradiation field size.

Development of a compact tritium activity monitor and first tritium measurements

To develop a convenient tool for in-line tritium gas monitoring, the TRitium Activity Chamber Experiment (TRACE) was built and commissioned at the Tritium Laboratory Karlsruhe (TLK). The detection system is based on beta-induced X-ray spectrometry (BIXS), which observes the bremsstrahlung X-rays generated by tritium decay electrons in a gold layer. The setup features a measuring chamber with a gold-coated beryllium window and a silicon drift detector. Such a detection system can be used for accountancy and process control in tritium processing facilities like the Karlsruhe Tritium Neutrino Experiment (KATRIN). First characterization measurements with tritium were performed. The system demonstrates a linear response between tritium partial pressure and the integral count rate in a pressure range of 1Pa up to 60Pa. Within 100s measurement time the lower detection limit for tritium is (143.63±5.06)·104Bq. The system stability of TRACE is limited by a linear decrease of integral count rate of 0.041%/h. This decrease is most probably due to exchange interactions between tritium and the stainless steel walls. By reducing the interaction surface with stainless steel, the decrease of the integral count rate was reduced to 0.008%/h. Based on the first results shown in this paper it can be concluded that TRACE is a promising complement to existing tritium monitoring tools.