Bremsstrahlung Source Research Articles

Collimation principles of a hollow X-ray microbeam for high-contrast cytoplasm irradiation.

A Monte Carlo simulation was used to assess the performance of a collimated hollow X-ray microbeam for subcellular cytoplasm irradiation. A high-Z coaxial collimation structure with an inner core for nucleus shielding was investigated. Two key performances, the extraction efficiency (cytoplasm dose per unit incident fluence) and the dose contrast (cytoplasm-to-nucleus dose ratio), were evaluated regarding the influences of the material, geometry and physical arrangements of the collimator, target dish and incident beam source. Simulation results demonstrate that a gold coaxial structure with a practical collimation geometry of a 1-mm length, 10-μm inner diameter and 200-μm outer diameter, with the top exit closely attached (with a minimized air gap) to the bottom of a cell dish with a 3-μm thick Mylar film is recommended for cytoplasm irradiation of adherent mammalian cells. For a synchrotron source in the energy range < 10keV, a dose contrast of approximately 100 can be achieved. For a bremsstrahlung source <30-kV tube voltage, a dose contrast of approximately 50-100 can still be achieved. General principles are summarized with further explanations of the performance of the hollow X-ray microbeam.

Photofission delayed gamma-ray measurements in a large cemented radioactive waste drum during LINAC irradiation

Nuclear materials characterization in 870 L cemented waste drums is challenging due to significant neutron and gamma ray attenuation. Among the existing non-destructive approaches, photon active interrogation is of particular interest. A LINAC accelerates electrons to energies greater than 10 MeV, leading to highly penetrating interrogating bremsstrahlung photons that can reach nuclear materials in the depth of the 870 L waste drum and allow the detection of delayed gamma rays emitted by photofission products. Because the interrogating photon and neutron fluxes are extremely high during irradiation, measurements with high purity germanium detectors are usually performed after a long irradiation time, for example by moving the detector or the waste drum. Therefore, such measurements are only sensitive to delayed gamma rays associated to photofission products having sufficient long half-life of at least tens of seconds, which cuts a valuable signal coming from fission products with a shorter half-life. In this paper, we report gamma rays measurements of very short lived photofission products using a 3 in × 3 in cylindrical LaBr3(Ce) fast scintillation detector. A depleted uranium sample was irradiated by a pulsed bremsstrahlung source with maximum energy 17.5 MeV in a macro pulsing mode (1 s irradiation, 2 s cooling). This allowed to acquire a strong delayed gamma signal within a time window of 2 s.A clear signature of nuclear materials was observed even in the depth of a concrete mock-up, with an excellent signal-to-noise ratio beyond 3.5 MeV where the background of nonnuclear activated materials is negligible. These results are compared to a semi analytical model that qualitatively agrees but underestimates the measurements by a constant factor 1.7, probably caused by a wrong beam intensity normalization. Indeed, in this work the LINAC pulse time structure (macro pulsing) was different from its nominal working point used to characterize the beam (usual pulsing mode). Since it allows direct calculations of the detector response to delayed gamma-ray photofission measurements, this model is a fast calculation alternative to time-consuming Monte Carlo simulations, in view of further studies that will follow this feasibility demonstration.

Micro-focus computed tomography for turbine blade based on all-optical bremsstrahlung source

Computed tomography is a major technique for nondestructive detection of internal defects of dense materials and large-size devices. It is widely used in material science, railway, aerospace, national defense, military industry and other industries. At present, conventional high-energy industrial computed tomography system uses the X-ray source based on traditional thermionic RF electron gun, which can only provide millimeter source size, thus limiting its imaging spatial resolution. A high-energy micro-focus X-ray source is the key means to realize high-resolution high-energy industry computed tomography. As an emerging accelerator technology, the laser wakefield accelerator is a promising candidate for the micro-focus high-energy industrial computed tomography. This article reports experimental results of a micro-focus X-ray source based on laser wakefield acceleration and a computed tomography for a turbine blade. Using a 20 TW Ti: sapphire laser system, an electron beam with a charge of (140±44) pC is generated through ionization-induced injection, and then an all-optical bremsstrahlung X-ray source with an accumulated source size of 25 μm is obtained by using a 1.5 mm tungsten target. Using this source, a preliminary compressed-sensing-based computed tomography for a turbine blade is performed.

Influence of a low-Z thin substrate on a microwire hard x-ray source driven by a picosecond laser pulse for point-projection x-ray radiography

In the point-projection hard x-ray radiography of dense matter, for example, an inertial confinement fusion implosion capsule at stagnation time, a picosecond laser driven gold microwire is used to produce a short pulse point, bremsstrahlung hard x-ray source. The microwire was held by a low-Z CH thin substrate commonly used to promote experimental performance. We explored the influence of the low-Z thin substrate on the microwire bremsstrahlung hard x-ray source via particle-in-cell and Monte Carlo simulations. It was shown that both of the microwires, with or without the low-Z thin substrate, could emit more intense hard x-ray radiation than the radiator buried in the equal-density substrate, which benefited from efficient electron recirculation. The freestanding microwire exhibited further enhanced electron recirculation compared to that with the low-Z thin substrate, while the increased hot electrons were only present for the energetic electrons of &amp;gt;1 MeV. Thus, the freestanding microwire could produce significantly more intense MeV gamma x-ray emission with respect to that with the substrate, but an ignorable increment was exhibited at the softer x-ray emission of 10–200 keV. These results provided valuable insights into the design of backlighter targets in point-projection x-ray radiography, such as a freestanding microwire being preferred in MeV gamma-ray radiography, while the microwire with the CH thin substrate could be used in the 10–200 keV hard x-ray Compton radiography of an implosion capsule.

Background Microwave Emission and Microflares in Young Active Region 12635

Abstract The goal of this work is to study the atmospheric heating above isolated AR 12635 during a period in which a quasistationary increase in microwave and soft X-ray emission is combined with a series of B- and C-class microflares. Analysis of photospheric vector magnetograms showed that an increase in the SXR brightness lasting 14 hours was observed during the simplification of the magnetic structure and the growth of vertical currents in the head part of the active region. A long-term increase of SXR and microwave emission occurred when the total unsigned vertical current exceeded the critical value and coincided in time with the increased level of the emission measure calculated from the GOES X-ray data. Against the background of quasistationary emission, microflares lasting 6–10 minutes occurred. In the hard X-ray range, bursts are recorded with RHESSI channels up to 25 keV. In microwave emission, pulsed and smooth components are distinguished during microflares. The first component was recorded in the 4.5–7.5 GHz range at the beginning of microflares and it is generated by a small population of relativistic electrons by the gyrosychrotron mechanism. The smooth component of the bursts dominated at 17 GHz and was emitted by bremsstrahlung. It is shown that the sources of quasistationary emission and microflares coincide with each other and with the bremsstrahlung source calculated from the differential emission measure obtained from the EUV maps. Coronal magnetic field reconstruction shows that the release of energy on both timescales occurs in a stably existing bundle of magnetic field lines.

Development of control mechanisms for a laser wakefield accelerator-driven bremsstrahlung x-ray source for advanced radiographic imaging

A high power laser was used to accelerate electrons in a laser-driven wakefield accelerator. The high energy electrons were then used to generate an x-ray beam by passing them through a converter target. This bremsstrahlung source was characterised and used to perform penetrative imaging of industrially relevant samples. The photon spectrum had a critical energy in excess of 100 MeV and a source size smaller than the resolution of the diagnostic (150 µm). Simulations indicate a significantly smaller source is achievable. Variations in the x-ray source characteristics were realised through changes to the plasma and converter parameters while simulations confirm the adaptability of the source. Imaging of high areal density objects with 150 µm resolution was performed, demonstrating the unique advantages of this novel source.

A Study of a Method for Determining the Size of a Bremsstrahlung Focal Spot Using a Slit Collimator

A computer model of a bremsstrahlung source based on a 4-MeV betatron has been corrected upon measuring the focal spot using a new version of the slit-collimator method. Based on this model, an analysis of possible sources of an error in measuring the focal spot is performed, thus providing the reliability of experimental results.

Detectability of flat microdefects in radiographic images obtained using linear microfocus bremsstrahlung source based on 18 MeV betatron with narrow target inside

For the determination of ability of microfocus Bremsstrahlung (Bs) source based on B-18 betatron to detect flat microgaps and microinclusions in heavy material products the investigations were carried out. The radiographic images of 10 μm gaps and 13 μ m tantalum (Ta) foil into steel bulk which were oriented at different angles with respect to the direction of radiation were investigated. The assembly of four steel blocks having 10 μm gaps between their neighbor surfaces was placed on goniometer. The 13 μm Ta foil having the length of 4 mm along radiation beam was mounted in a plastic holder which was also placed on the goniometer. For modeling narrow gaps and thin inclusions inside the bulk of steel detail, the experimental samples were placed before a thick steel plate. The radiographic images of the samples were obtained with a 2.4-fold magnification at different orientations of narrow gaps and Ta foil with respect to the radiation beam and at the thick steel plates of different thicknesses. The results illustrate high sensitivity of detecting of the microgaps inside steel bulk and flat microinclusions from heavy material in the bulk of detail made from a lighter material due to the microfocus of Bs source.

Bremsstrahlung emission profile from intense laser-solid interactions as a function of laser focal spot size

The bremsstrahlung x-ray emission profile from high intensity laser-solid interactions provides valuable insight to the internal fast electron transport. Using penumbral imaging, we characterise the spatial profile of this bremsstrahlung source as a function of laser intensity by incrementally increasing the laser focal spot size on target. The experimental data shows a dual-source structure; one from the central channel of electrons, the second a larger substrate source from the recirculating electron current. The results demonstrate than an order of magnitude improvement in the intensity contrast between the two x-ray sources is achieved with a large focal spot, indicating preferable conditions for applications in radiography. An analytical model is derived to describe the transport of suprathermal electron populations that contribute to substrate and central channel sources through a target. The model is in good agreement with the experimental results presented here and furthermore is applied to predict laser intensities for achieving optimum spatial contrast for a variety of target materials and thicknesses.

Calculation of Electron-Beam Dynamics in a C-Band Accelerator for a Radiotherapy Complex

The dynamics of the electron beam in a C-band linear accelerator, a bremsstrahlung source with a boundary energy switched between 2.5 MeV and 6 MeV, which is intended for stereotactic and three-dimensional conformal radiotherapy in static and rotational modes, was calculated.

Compact high energy x-ray spectrometer based on forward Compton scattering for high intensity laser plasma experiments.

This article describes the design and presents recent results from testing and calibration of a forward Compton scattering high energy X-ray spectrometer. The calibration was performed using a bremsstrahlung source on the photon scattering facility at the Electron linac for beams with high brilliance and low emittance accelerator at Helmholtz-Zentrum Dresden-Rossendorf, which provides high energy X-ray photons with energies up to 18 MeV. The calibration was conducted at different bremsstrahlung end point energies-10.5, 13, 15, and 18 MeV. Experimental spectra show a systematic increase in the maximum energy, photon temperature, and flux. The spectrometer is effective for an energy range of 4-20 MeV with energy resolution. The spectrometer operates in low vacuum with pressure less than 0.1 mbar. Experimental tests showed that operating such a spectrometer in air causes a spuriously enhanced high energy signal due to Compton scattering of photons within air. The article also describes the design and shielding considerations which helped to achieve a dynamic range greater than 30 with this spectrometer. The comparison between the experimental results and Monte Carlo simulations are also presented.

OA083] Toward 4d micro-CT and radiotherapy of small animals using all-optical, ultrashort X-ray sources: feasibility study and preliminary experimental results

Purpose All-optical, laser-driven X/gamma-ray sources, based on the primary electron acceleration via the Laser WakeField Acceleration (LWFA) process, have now entered a mature phase in terms of beam parameters, shot-to-shot stability, and reliability, so as to be considered as promising tools in medical physics. The high electron acceleration gradient results in the possibility of accelerating electrons up to the 100s MeV range over very short distances and thus opening the way to the generation of high energy photons using “table-top” machines. The PRELUDE (PREclinical Laser-based Ultrafast Diagnostics and therapy) project is ongoing, as a collaboration among different Italian Institutions aimed at studying the application of a laser-driven X-ray source for 4D micro-CT and radiotherapy of small animals. Methods As a first step, the exploitation of a Bremsstrahlung source driven by a LWFA, plasma-based accelerator is investigated, both theoretically and experimentally. The preliminary experimental results focused on characterizing the photon source, based on a 10TW ultrashort laser system for micro-CT of small animals is discussed. Issues related to both the primary electron acceleration and the generation of secondary photons via the Bremsstrahlung process will be discussed, including both numerical and experimental results. Results The X-ray spectrum, beam intensity, e- contamination and photon dosimetry have been simulated using the GEANT4 toolkit on top of experimental measurements of the e- spectrum obtained using our setup and numerical estimations of the accelerated charge per pulse. Proof-of-principle radiographic images of physical phantoms obtained with photostimulable phosphor image plates are presented. Conclusions We presented a system for small animal 4D-CT and radiotherapy based on a laser-driven X-ray source. The results of a theoretical and numerical study of a 4D micro-CT device based on a more advanced all-optical X-ray source based on Thomson scattering will be presented.

Bremsstrahlung hard x-ray source driven by an electron beam from a self-modulated laser wakefield accelerator

An x-ray source generated by an electron beam produced using a Self-Modulated Laser Wakefield Accelerator (SM-LWFA) is explored for use in high energy density science facilities. By colliding the electron beam, with a maximum energy of 380 MeV, total charge of >10 nC and a divergence of 64 × 100 mrad, from a SM-LWFA driven by a 1 ps 120 J laser, into a high-Z foil, an x/gamma-ray source was generated. A broadband bremsstrahlung energy spectrum with temperatures ranging from 0.8 to 2 MeV was measured with an almost 2 orders of magnitude flux increase when compared with other schemes using LWFA. GEANT4 simulations were done to calculate the source size and divergence.

Microfocus Bremsstrahlung Source Based on a Narrow Internal Target of a Betatron

The paper addresses the research into the properties of bremsstrahlung generated by interaction of the internal electron beam of the 18 MeV betatron with narrow targets, 50 and $$8 \,\upmu \hbox {m}$$ thick Si crystals and $$13 \,\upmu \hbox {m}$$ thick Ta foil with a length of 4 mm along the electron beam, mounted in the goniometer inside the betatron chamber. The radiation beams generated in the targets were used to obtain the images of a microstructure of thin wire pairs and an object that consisted of four steel bars with $$10\, \upmu \hbox {m}$$ gaps between them. The images indicate high absorption contrast of their components due to a small horizontal size of the radiation source the width of which in the cases of Si crystals and Ta foil was 30-, 187- and 115-fold smaller than the diameter of the electron beam, respectively. The edge phase-contrast was also observed due to high spatial coherency of the radiation with the linear microfocus generated in the source based on the B-18 betatron with a narrow target inside.

New microfocus bremsstrahlung source based on betatron B-18 for high-resolution radiography and tomography

New microfocus source of hard bremsstrahlung (photon energy > 1 MeV), based on the betatron B-18 with a narrow Ta target inside, for high-resolution radiography and tomography is presented. The first studies of the source demonstrate its possibilities for practical applications to detect the microdefects in products made from heavy materials and to control gaps in joints of parts of composite structures of engineering facilities. The radiography method was used to investigate a compound object consisting of four vertically arranged steel bars between which surfaces were exposed gaps of 10 μm in width. The radiographic image of the object, obtained with a magnification of 2.4, illustrates the good sensitivity of detecting the gaps between adjacent bars, due to the small width of the linear focus of the bremsstrahlung source.

Emittance Growth in the DARHT-II Linear Induction Accelerator

The Dual-Axis Radiographic Hydrotest (DARHT) facility uses bremsstrahlung radiation source spots produced by the focused electron beams from two linear induction accelerators (LIAs) to radiograph large hydrodynamic experiments driven by high explosives. Radiographic resolution is determined by the size of the source spot, and beam emittance is the ultimate limitation to spot size. Some of the possible causes for the emittance growth in the DARHT LIA have been investigated using particle-in-cell (PIC) codes, and are discussed in this article. The results suggest that the most likely source of emittance growth is a mismatch of the beam to the magnetic transport, which can cause beam halo.

Abstract ID: 135 Characterization of an X-ray source based on laser-target interaction using the Geant4 Monte Carlo toolkit

The aims of our work was to design, study and optimize the main characteristics of an X-ray bremsstrahlung source based on a laser-driven electron beam accelerated via Laser Wake-Field Acceleration. This study is performed using a custom Monte Carlo-Geant4 application, called IORT-Laser-therapy. The X-ray source is designed on top of the laser-driven electron accelerator already running at the Intense Laser Irradiation Laboratory of the INO-CNR in Pisa. It is based upon a 10 TW laser system delivering 400 mJ energy at a 10 Hz repetition rate. This accelerator has been already proved to be able to deliver electron bunches with up to around 80 MeV with energy spread down to around 25% and bunch charge ranging from few tens of pC up to few nC. Electron interactions are simulated, starting form an exponentially decreasing e- energy spectrum; a thin tungsten foil has been used in order to generate X-rays via bremsstrahlung. The Monte Carlo application allows studying many features of the resulting X-ray beam such as (i) the conversion efficiency using different foil thicknesses, (ii) the X-ray source size (iii) the particle contamination of the output beam, (iv) the out-of-beam scattered radiation for external shielding design. The need for a dipole magnet to get rid of residual electrons in the output beam is also investigated. Besides conversion efficiency, the simulation of different scatter foil thicknesses will also enable us to investigate the dependence of the beam divergence upon this parameter. Radiation protection is another important design goal that can take advantage of our application. More specifically, we will study the dose distribution around the chamber which main contribution comes from back-scattered electrons by scatter foil and other collimation elements, as well as potential contributions of neutrons produced by photonuclear reactions from the high energy tails of the X-ray beam. The final project aims are design and optimization a proof-of-principle micro-CT/RT platform for small animals exploiting the unique features of a novel concept all-optical bremsstrahlung X-ray beam. This research was supported by the Italian Ministry of Research (MIUR) within the PRIN project “PRELUDE” (PRIN-2015, n.20154F48P9).

Printable organometallic perovskite enables large-area, low-dose X-ray imaging.

Medical X-ray imaging procedures require digital flat detectors operating at low doses to reduce radiation health risks. Solution-processed organic-inorganic hybrid perovskites have characteristics that make them good candidates for the photoconductive layer of such sensitive detectors. However, such detectors have not yet been built on thin-film transistor arrays because it has been difficult to prepare thick perovskite films (more than a few hundred micrometres) over large areas (a detector is typically 50 centimetres by 50 centimetres). We report here an all-solution-based (in contrast to conventional vacuum processing) synthetic route to producing printable polycrystalline perovskites with sharply faceted large grains having morphologies and optoelectronic properties comparable to those of single crystals. High sensitivities of up to 11 microcoulombs per air KERMA of milligray per square centimetre (μC mGyair-1 cm-2) are achieved under irradiation with a 100-kilovolt bremsstrahlung source, which are at least one order of magnitude higher than the sensitivities achieved with currently used amorphous selenium or thallium-doped cesium iodide detectors. We demonstrate X-ray imaging in a conventional thin-film transistor substrate by embedding an 830-micrometre-thick perovskite film and an additional two interlayers of polymer/perovskite composites to provide conformal interfaces between perovskite films and electrodes that control dark currents and temporal charge carrier transportation. Such an all-solution-based perovskite detector could enable low-dose X-ray imaging, and could also be used in photoconductive devices for radiation imaging, sensing and energy harvesting.

Laser-plasmas in the relativistic-transparency regime: Science and applications.

Laser-plasma interactions in the novel regime of relativistically induced transparency (RIT) have been harnessed to generate intense ion beams efficiently with average energies exceeding 10 MeV/nucleon (>100 MeV for protons) at “table-top” scales in experiments at the LANL Trident Laser. By further optimization of the laser and target, the RIT regime has been extended into a self-organized plasma mode. This mode yields an ion beam with much narrower energy spread while maintaining high ion energy and conversion efficiency. This mode involves self-generation of persistent high magnetic fields (∼104 T, according to particle-in-cell simulations of the experiments) at the rear-side of the plasma. These magnetic fields trap the laser-heated multi-MeV electrons, which generate a high localized electrostatic field (∼0.1 T V/m). After the laser exits the plasma, this electric field acts on a highly structured ion-beam distribution in phase space to reduce the energy spread, thus separating acceleration and energy-spread reduction. Thus, ion beams with narrow energy peaks at up to 18 MeV/nucleon are generated reproducibly with high efficiency (≈5%). The experimental demonstration has been done with 0.12 PW, high-contrast, 0.6 ps Gaussian 1.053 μm laser pulses irradiating planar foils up to 250 nm thick at 2–8 × 1020 W/cm2. These ion beams with co-propagating electrons have been used on Trident for uniform volumetric isochoric heating to generate and study warm-dense matter at high densities. These beam plasmas have been directed also at a thick Ta disk to generate a directed, intense point-like Bremsstrahlung source of photons peaked at ∼2 MeV and used it for point projection radiography of thick high density objects. In addition, prior work on the intense neutron beam driven by an intense deuterium beam generated in the RIT regime has been extended. Neutron spectral control by means of a flexible converter-disk design has been demonstrated, and the neutron beam has been used for point-projection imaging of thick objects. The plans and prospects for further improvements and applications are also discussed.

Bremsstrahlung Dose Yield for High-Intensity Short-Pulse Laser-Solid Experiments.

A bremsstrahlung source term has been developed by the Radiation Protection (RP) group at SLAC National Accelerator Laboratory for high-intensity short-pulse laser-solid experiments between 1017 and 1022 W cm-2. This source term couples the particle-in-cell plasma code EPOCH and the radiation transport code FLUKA to estimate the bremsstrahlung dose yield from laser-solid interactions. EPOCH characterizes the energy distribution, angular distribution, and laser-to-electron conversion efficiency of the hot electrons from laser-solid interactions, and FLUKA utilizes this hot electron source term to calculate a bremsstrahlung dose yield (mSv per J of laser energy on target). The goal of this paper is to provide RP guidelines and hazard analysis for high-intensity laser facilities. A comparison of the calculated bremsstrahlung dose yields to radiation measurement data is also made.