Quasi-monochromatic X-ray Research Articles

A quasi-monochromatic X-rays source for art painting pigments investigation

Monochromatic X-ray sources can be used for several applications, like in medicine or in studying our cultural heritage. We are investigating imaging systems based on a tuneable energy band X-ray source, to obtain an element mapping of painting layers using the K-edge technique. The narrow energy band beams are obtained with conventional X-ray source via Bragg diffraction on a mosaic crystal; such an analysis has been performed at different diffraction angles, tuning the energy to investigate spectra of interest from the artistic point of view, like zinc and copper. In this paper the characteristics of the system in terms of fluence rate are reported, and first results of this technique on canvas samples and painting are presented.

Table-top kHz hard X-ray source with ultrashort pulse duration for time-resolved X-ray diffraction

The interaction of ultrashort laser pulses with solid state targets is studied concerning the production of short X-ray pulses with photon energies up to about 10 keV. The influence of various parameters such as pulse energy, repetition rate of the laser system, focusing conditions, the application of prepulses, and the chirp of the laser pulses on the efficiency of this highly nonlinear process is examined. In order to increase the X-ray flux, the laser pulse energy is increased by a 2nd multipass amplifier from 750 μJ to 5 mJ. By applying up to 4 mJ of the pulse energy a X-ray flux of 4×1010 Fe K α photons/s or 2.75×1010 Cu K α photons/s are generated. The energy conversion efficiency is therefore calculated to η Fe≈1.4×10−5 and η Cu≈1.0×10−5. The X-ray source size is determined to 15×25 μm2. By focusing the produced X-rays using a toroidally bent crystal a quasi-monochromatic X-ray point source with a diameter of 56 μm×70μm is produced containing ≈104 Fe K α1 photons/s which permits the investigation of lattice dynamics on a picosecond or even sub-picosecond time scale. The lattice movement of a GaAs(111) crystal is shown as a typical application.

Image quality simulations in X-ray mammography

The application of tunable monochromatic X-rays to mammography can improve the image quality and reduce the radiation dose to the patient. A new generation of quasi-monochromatic, high-flux X-ray sources is currently under development, based on Thomson scattering of photons produced by a laser on a highly focused electron beam. In this paper we investigate the effect of different spectral distributions on the image contrast on 2 cm, 4 cm, 6 cm, 8 cm breast mammographic phantoms containing details of different composition (tumor mass and calcification details) and thickness. In the simulations we assume a homogeneous breast composition and three compositions (25%; 50% and 75% glandular) are investigated. We simulate monochromatic, quasi-monochromatic and polychromatic X-ray sources in order to define the optimal energies that maximize the image quality parameter. In particular we compare the simulations of the Gaussian quasi-monochromatic spectra. having different energy standard deviations (1, 2, 3, 4, 5 keV) with traditional X-ray tubes spectra. Results show that Gaussian spectra having an energy spread of about 1 keV standard deviation call improve the image quality of about 30% with respect to traditional X-ray tube ones.

Development of a Multi-Energy CT for Small Animals: Characterization of the Quasi-Monochromatic X-Ray Source

A new multi-energy CT for small animals is operative (now only in scanning mode) at the Physics Department of the University of Bologna. The system makes use of a set of quasi-monochromatic X-ray beams produced by means of an Highly-Oriented Pyrolytic Graphite Bragg monochromator. This source is able to provide beams with energy tunable in a range from 20 to 70 keV. Here we present a complete characterization of the source. A theoretical model of the source has been analyzed, according to the known Zachariasen's theory for diffracting crystals. The beams have also been characterized in resolution and intensity, over the accessible range, and we present here some measured spectra. The monochromator system demonstrated an energy spread of about 3 keV (Full Width at Half Maximum-FWHM) at a beam energy of 26 keV. At the same energy, the intensity of the output beam is about 6% of the primary beam.

Development of a Compact X-ray Source and Super-sensitization of Photo Resists for Soft X-ray Imaging

A compact soft X-ray source via inverse Compton scattering has been developed at Waseda University. The energies of the generated X-rays are within water window region (250 - 500 eV) and development of a soft X-ray microscope is expected which can get the elemental mapping of carbon and/or nitrogen without dehydration. We have studied to develop a high resolution soft X-ray imaging system with photo resists for nanoscale observation. However, the yield of generated X-rays had been too small for the practical use of the soft X-ray microscopy. To enhance the X-ray yield, we have upgraded the generation system and succeeded in increasing the detected photons 10-fold. Total generated photons were estimated to be over 1.5E+5 photons/s. Also, supersensitization of photo resists has been attempted to reduce the required X-ray amount. By irradiating quasi-monochromatic X-rays in the water window region from synchrotron radiation at BL12 of the SAGA-LS, the sensitivity of a deep-UV photo resist, TDUR-P722 (Tokyo Ohka Kogyo Co., Ltd) was evaluated. After UV light (including 254 nm) exposure up to the sensitivity threshold and baking as PEB process, it was found that the resist becomes more sensitive. This UV pre-exposure method reduced the required 400 eV X-ray amount by over 65 %.

Development of a Compact X-ray Source and Super-sensitization of Photo Resists for Soft X-ray Imaging

A compact soft X-ray source via inverse Compton scattering has been developed at Waseda University. The energies of the generated X-rays are within region (250 - 500 eV) and development of a soft X-ray microscope is expected which can get the elemental mapping of carbon and/or nitrogen without dehydration. We have studied to develop a high resolution soft X-ray imaging system with photo resists for nanoscale observation. However, the yield of generated X-rays had been too small for the practical use of the soft X-ray microscopy. To enhance the X-ray yield, we have upgraded the generation system and succeeded in increasing the detected photons 10-fold. Total generated photons were estimated to be over 1.5E+5 photons/s. Also, super-sensitization of photo resists has been attempted to reduce the required X-ray amount. By irradiating quasi-monochromatic X-rays in the water window region from synchrotron radiation at BL12 of the SAGA-LS, the sensitivity of a deep-UV photo resist, TDUR-P722 (Tokyo Ohka Kogyo Co., Ltd) was evaluated. After UV light (including 254 nm) exposure up to the sensitivity threshold and baking as PEB process, it was found that the resist becomes more sensitive. This UV pre-exposure method reduced the required 400 eV X-ray amount by over 65 %.

Parametric X-rays generated by electrons in multilayer mirrors mounted inside a betatron

The measured characteristics of tunable, quasi-monochromatic X-rays from thin multilayer mirrors used as radiators mounted inside a 35 MeV betatron chamber are presented. Parametric X-ray radiation (PXR) was generated by 15–33 MeV electrons passing through two radiators consisted of a few hundreds of W/B4C bilayers with period of 14.86 and 18 A. Shifts of the PXR spectra were measured as the orientation of the multilayer radiators relative to the incident electron beam was changed. The PXR flux was determined by comparison with the yield of L fluorescence generated by electrons in the W layers of the multilayer.

Phase contrast imaging simulation and measurements using polychromatic sources with small source-object distances

Phase contrast imaging is a technique widely used in synchrotron facilities for nondestructive analysis. Such technique can also be implemented through microfocus x-ray tube systems. Recently, a relatively new type of compact, quasimonochromatic x-ray sources based on Compton backscattering has been proposed for phase contrast imaging applications. In order to plan a phase contrast imaging system setup, to evaluate the system performance and to choose the experimental parameters that optimize the image quality, it is important to have reliable software for phase contrast imaging simulation. Several software tools have been developed and tested against experimental measurements at synchrotron facilities devoted to phase contrast imaging. However, many approximations that are valid in such conditions (e.g., large source-object distance, small transverse size of the object, plane wave approximation, monochromatic beam, and Gaussian-shaped source focal spot) are not generally suitable for x-ray tubes and other compact systems. In this work we describe a general method for the simulation of phase contrast imaging using polychromatic sources based on a spherical wave description of the beam and on a double-Gaussian model of the source focal spot, we discuss the validity of some possible approximations, and we test the simulations against experimental measurements using a microfocus x-ray tube on three types of polymers (nylon, poly-ethylene-terephthalate, and poly-methyl-methacrylate) at varying source-object distance. It will be shown that, as long as all experimental conditions are described accurately in the simulations, the described method yields results that are in good agreement with experimental measurements.

Imaging-therapy computed tomography with quasi-monochromatic X-rays

Introduction Computed tomography (CT) is a widespread and highly precise technique working in the energy range around 50–100 keV. For radiotherapy, however, the MeV energy range enables a better dose distribution. This gap between diagnosis and therapy can be overcome by the use of a modified CT machine in combination with heavy elements targeted to the tumour and used as photoelectric radiation enhancer. Materials and methods The experimental setup consists of an X-ray optical module mounted at the exit of the X-ray tube of a clinical CT. The module converts the standard fan-shaped beam into a high intensity, monochromatized and focused beam. The radiation was characterized using an energy-dispersive detection system calibrated by synchrotron radiation and gel dosimetry. The photoelectric radiation enhancement for different elements was calculated and experimentally verified. Results The X-ray optical module filters selectively the energy of the tungsten Kα-emission line (59.3 keV) with a full width at half maximum (FWHM) of 5 keV and focused the radiation onto a focal spot which coincides with the isocentre of the gantry. This results in a steep dose gradient at the centre of rotation qualified for locoregional radiation therapy. The photon energy of the quasi-monochromatic radiation agrees with the energy range of maximal photoelectric dose enhancement for gadolinium and iodine. Conclusion An additional X-ray optical module optimized for targeted therapy and photoelectric dose enhancement allows the combination of diagnosis and radiotherapy on a clinical CT.

A compact micro-beam system using a tapered glass capillary for proton-induced X-ray radiography

A compact micro-beam system, containing a tapered glass capillary tube with a tip diameter on the order of 10μm, was constructed to examine the applicability of capillary-generated micro-beams to high-contrast radiography based on proton-induced quasi-monochromatic X-rays. The transport efficiency of swift protons (2–3MeV) through the capillary was examined as a function of the capillary tilt angle and the capillary tip diameter. We obtained transport efficiencies of approximately three times larger than would be expected from the geometrical shape of the capillary. This enhancement indicates that a focusing effect occurred in the capillary. A metallic thin foil was irradiated with the micro-beam and quasi-monochromatic X-rays were produced. By calculating the X-ray yields induced by proton bombardment in the foil and comparing them with the X-ray counts observed at the detector, the throughput efficiency of the X-ray imaging system was evaluated. We demonstrated magnification radiography of a small object to show that a spatial resolution on the order of 10μm was achievable in our system.

Effect of x‐ray energy dispersion in digital subtraction imaging at the iodine ‐edge—A Monte Carlo study

The effect of the energy dispersion of a quasi-monochromatic x-ray beam on the performance of a dual-energy x-ray imaging system is studied by means of Monte Carlo simulations using MCNPX (Monte Carlo N-Particle eXtended) version 2.6.0. In particular, the case of subtraction imaging at the iodine K-edge, suitable for angiographic imaging application, is investigated. The average energies of the two beams bracketing the iodine K-edge are set to the values of 31.2 and 35.6 keV corresponding to the ones obtained with a compact source based on a conventional x-ray tube and a mosaic crystal monochromator. The energy dispersion of the two beams is varied between 0 and 10 keV of full width at half-maximum (FWHM). The signal and signal-to-noise ratio produced in the simulated images by iodine-filled cavities (simulating patient vessels) drilled in a PMMA phantom are studied as a function of the x-ray energy dispersion. The obtained results show that, for the considered energy separation of 4.4 keV, no dramatic deterioration of the image quality is observed with increasing x-ray energy dispersion up to a FWHM of about 2.35 keV. The case of different beam energies is also investigated by means of fast simulations of the phantom absorption.

Nanosecond x-Ray diffraction from polycrystalline and amorphous materials in a pinhole camera geometry suitable for laser shock compression experiments

Nanosecond pulses of quasimonochromatic x-rays emitted from the K shell of ions within a laser-produced plasma are of sufficient spectral brightness to allow single-shot recording of powder diffraction patterns from thin foils of order millimeter diameter. Strong diffraction signals have been observed in a cylindrical pinhole camera arrangement from both polycrystalline and amorphous foils, and the experimental arrangement and foil dimensions are such that they allow for laser shocking or quasi-isentropic loading of the foil during the diffraction process.

Dependence of image quality on energy spread for a Bragg diffraction based radiography system

The aim of this work is to investigate the relationship between contrast and energy resolution of a quasi-monochromatic X-ray system based on Bragg diffraction on a mosaic crystal. Three different energies have been considered: 18, 22 and 26 keV. A commercial phantom containing large and small area details and a digital detector have been used. Results show that for large area details and for a certain value of energy, the energy spread of the incident X-ray beams produces a small reduction of the contrast, while for small area details the high reduction of the contrast is principally due to the spatial resolution properties of the system.

Phase-contrast x-ray imaging with intense ArKα radiation from femtosecond-laser-driven gas target

Intense ArKα x ray with very little continuum background has been generated using a dense Ar gas irradiated with an intense femtosecond laser, with the measured flux of 1.2×103photons∕mrad2/pulse. This compact quasimonochromatic x-ray source, with a source size of only 12μm, has been applied to x-ray radiographic imaging of a biological specimen, resulting in high-resolution, high quality phase-contrast images. Correlation between this intense Kα emission with the laser channeling in the Ar gas is discussed.

High power laser pulse circulation experiment for compact quasi-monochromatic tunable X-ray source

Laser electron Compton scattering monochromatic tunable X-ray source using X-band (11.424GHz) electron linear accelerator and Q-switch Nd:YAG laser is under construction at Nuclear Professional School, the University of Tokyo. To enhance the X-ray intensity, we installed a laser circulation system. Now, we are performing the circulation experiment by using a high power laser (1.4J, 532nm). We confirmed the laser pulse circulated in the optical circuit more than 15 times and the laser intensity is enhanced about 3.5 times.

Design study of the KAERI Compton X-ray source depending on the laser intensity in the linear or non-linear regime

Quasi-monochromatic X-rays can be generated via Compton backscattering at the KAERI superconducting (SC) radio-frequency (RF) Linac system. The KAERI SC RF Linac with one 352 MHz cryomodule is now operating at 10 MeV. For a few keV Compton X-rays, an electron beamline is designed at the straight section, just after the SC linac, while an optical beamline is designed and fabricated based on the fiber laser delivery. Both will be installed in fall, 2006. In this paper, we estimate the parameters of Compton X-rays at a given system using three different commercial lasers and suggest the scheme to generate higher harmonics using an intense ultra-short laser.

Quasimonochromatic x-rays generated from nonlinear Thomson backscattering

The nonlinear Thomson backscattering in a circularly polarized Gaussian laser pulse is investigated and spectral characteristics of the emission are discussed. It is indicated that the frequency of the emitted light is up-shifted by the nonlinear doppler effect. By using a properly focused laser beam or putting the electron before the focus, the variety of the nonlinear Doppler shift during the interaction can be minimized and quasimonochromatic x-rays are generated. Taking into account the emission power, the optimum situations for generating quasimonochromatic x-rays are explored.

A Compton X-ray source based on a SC linac at KAERI

A quasi-monochromatic X-ray source based on a KAERI SC linac system has been designed and is being manufactured now. 10 MeV 10 mA electron beam together with 20 W 1.06 μm laser beam will be used for 1.8 keV Compton X-ray generation with a few percentage of energy spread and 10 7 photons /s flux. A simple straight beamline was designed to deliver the electron beam with no degradation of its emittance and energy spread and to focus it to a proper size to produce the desired X-rays. We expect the first demonstration of 1.8 keV Compton X-ray generation in autumn 2006.

Two-Dimensional Measurements of X-ray Spectra Generated by Laser-Compton Scattering

Measurements of X-ray spectra generated by laser-Compton scattering are described. Basically, laser-Compton X-rays present distinctive characteristics, such as good-directivity, tunability, and a quasi-monochromatic X-ray spectrum. However, the actual X-ray spectrum is degraded by the effects of the broad spectrum of the laser pulse, and by the intrinsic spatial divergence of the electron bunch defined by the beam emittance. It is important to measure the spectral properties of laser-Compton X-rays for applications involving protein crystallography or mammography. The energy distribution in the forward direction can be observed using a front-illuminated deep-depletion X-ray charge-coupled device (CCD) detector. The spectral width of the measured X-rays within a detection angle of 4 mrad is estimated to be 5.0% (rms) for a CCD resolution of 2.6% (rms). These results can be accurately explained using a simple relationship between the electrons and the laser beam parameters.

Measurement of the energy distribution of parametric X-ray radiation from a double-crystal system

A parametric X-ray radiation (PXR) generator system was developed at the Laboratory for Electron Beam Research and Applications (LEBRA) at Nihon University; this PXR generator system is a tunable wavelength and quasi-monochromatic X-ray source constructed as one of the advanced applications of the LEBRA 125-MeV electron linear accelerator. The PXR beam which has characteristic of energy distribution.The theoretical values of energy distribution obtained at the output port were calculated to be approximately 300eV and 2keV at the central X-ray energies of 7keV and 20keV, respectively. In order to investigate the energy distribution, several measurements of the X-ray energy were carried out. The X-ray absorption of known materials and that of thin aluminum has been evaluated based on analyses of images taken using an imaging plate.The X-ray energy was deduced base on the identification of the absorption edges, and the energy distribution was estimated based on measurements using aluminum step method. In addition, an X-ray diffraction method using a perfect silicon crystal was employed, and spectra were measured using a solid state detector (SSD). The results of these experiments agreed with the calculated results. In particular, the well-defined absorption edges in the X-ray images and the typical rocking curves obtained by the measurement of the X-ray diffraction indicated that the distribution has a high-energy resolution.