Pulsed X-ray Source Research Articles

Accumulative dose response of CdZnTe detectors to 14.1 MeV neutrons

The accumulative dose response of CdZnTe (CZT) detectors to 14.1MeV neutrons is discussed experimentally in this paper. The Cockcroft–Walton Accelerator is used to obtain a steady neutron beam of 14.1MeV neutrons. A pulsed X-ray source is used to test the response parameters of the neutron-exposed CZT detectors under the pulse mode. The irradiation time (hours) is shorter relative to the time scales (years) where annealing effects occur. Time and linearity response is analyzed to evaluate the maximum dose rate of the CZT detectors and the pulse shape. The result shows that the experimental CZT detectors maintain stable response behaviors, while the maximum dose rate and the total accumulative dose are less than 106neutrons/(cm2·s) and 1010neutrons/cm2, respectively.

A method of evaluating the relative light yield of ST401 irradiated by pulsed neutron

High speed imaging technique is an effective method to test the information about pulsed neutron source. Imaging system is usually composed of a pinhole, a scintillator, an image intensifier and a charge-coupled device (CCD) camera. ST401 plastic scintillator is widely used to convert the neutron image into visible light image since it has features of high conversion efficiency and fast time response. When testing a pulsed neutron source of wide energy spectrum, we should evaluate the light yields of ST401 irradiated by neutrons with different energies and make the CCD camera exposed to the light appropriately. A 0.3 MeV pulsed X-ray source is often used to calibrate the imaging system because of its low cost than the D-T fusion neutron source. In this work, a method of evaluating the relative light yield of ST401 irradiated by 0.1-16 MeV neutron to 0.3 MeV X-ray is proposed.Geant4 Monte Carlo software is used to simulate the transport performances of neutrons and X-rays. The software package can simulate the transport process of photons. But the conversion factor of ray energy deposition into photons is unknown. It is difficult to calculate the number of photons generated in ST401 accurately. In this article, we calculate the relative light yield according to the energy of charged particles produced in ST401. Firstly, all information about the particle type, energy deposition, kinetic energy is monitored on event-by-event basis in GEANT4. Secondly, the complete history of the tracks is then used to calculate the light output from the scintillator according to the neutron response functions. Thirdly, the light output caused by charged particles going out of ST401 is deducted. Ratios of average light yield of 1 mm, 3 mm, 5 mm, 1 cm, 2 cm, 3 cm, 5 cm thick ST401 irradiated by 0.1-16 MeV neutron to 0.3 MeV X-ray are given. To confirm the correctness of the simulated result, validation experiment is carried out on IVA pulsed X-ray source and SGIII pulsed neutron source. The simulated ratio of average light yield of ST401 irradiated by one single 14 MeV neutron to 0.3 MeV X-ray has a discrepancy of less than 10% compared with the measured value. Compared with the results of experiment conducted on a constant current source, the simulated results have a maximum discrepancy of less than 44%. If CCD camera exposure 10%-90% of the full scale, the image will have high contrast and information loss can be avoided. According to the simulated results and the neutron yield, exposure can be easily set to be 60% of the full scale by adjusting the gain of the image intensifier. Assume that the simulated results have a 44% discrepancy, the actual exposure will be in a range of 34%-86% of the full scale. Underexposure and overexposure can be avoided by presetting the imaging system sensitivity appropriately based on the simulated results. It implies that the method proposed is effective in predicting the imaging system response to pulsed neutron with wide energy spectrum.

Experimental study on high dose rate response of cadmium zinc telluride detectors to pulsed X-ray

The linear response is the key property for a radiation detector to obtain accurate intensity of the radiation field. In this experiment, a high-intensity pulsed X-ray source, named “QiangGuang-I” is utilized to test the linear response of cadmium zinc telluride (CZT) detector. The total dose per pulse 20 cm from the pulse source is 200–3000 Gy. The full width at half maximum of each pulse is 20–30 ns, and the average energy of X-ray is approximately 1 MeV. Two detectors are placed in different intensities, and their responding curves are used to draw the Lissajous figure, analyzing the maximum energy dose rate of the CZT detector. The total dose of the pulsed X-ray into the experimental detectors is simultaneously measured by thermoluminescent dosimeter (TLD) chips. The result shows that the output of CZT detectors remains linear when the energy fluence rate is lower than 1017 MeV/(cm2·s).

The method of pulsed x-ray detection with a diode laser

A new class of pulsed X-ray detection methods by sensing carrier changes in a diode laser cavity has been presented and demonstrated. The proof-of-principle experiments on detecting pulsed X-ray temporal profile have been done through the diode laser with a multiple quantum well active layer. The result shows that our method can achieve the aim of detecting the temporal profile of a pulsed X-ray source. We predict that there is a minimum value for the pre-bias current of the diode laser by analyzing the carrier rate equation, which exists near the threshold current of the diode laser chip in experiments. This behaviour generally agrees with the characterizations of theoretical analysis. The relative sensitivity is estimated at about 3.3 × 10-17 C ⋅ cm2. We have analyzed the time scale of about 10 ps response with both rate equation and Monte Carlo methods.

Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics

Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x-rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x-ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x-rays have been poor at picking up excited state moieties from the unexcited ones. With time-resolved anti-Stokes resonant x-ray Raman scattering (AS-RXRS) performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x-rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe(CO)5 in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS-RXRS with transform-limited x-ray pulses is given—which will be covered experimentally by upcoming transform-limited x-ray sources.

Plasma-filled diode with a rod anode for repetitive pulsed X-ray sources

AbstractThe paper presents a cylindrical diode with a rod anode for repetitive pulsed intense X-ray sources. The diode uses a massive anode of diameter 1 cm, thus increasing the lifetime of the energy converter. The diode gap is preliminary filled with ions produced by cathode flare in a vacuum discharge, allowing electron beam pinching at a voltage of <200 kV. In the mode of pinching, the diode is an efficient source of high-power X rays. At a distance of 20 cm from the X-ray source, the radiation dose per pulse is 0.4 R at a peak power of 7 × 106 R/s. The full-width at half-maximum of the radiation pulse is 40 ns. The power in the diode is 1.8 GW at a beam current of 10 kA and exceeds the maximum power of the generator operating onto a matched load with constant resistance.

Energy Spectrum Measurement of High Power and High Energy (6 and 9 MeV) Pulsed X-ray Source for Industrial Use

Background: Industrial X-ray CT system is normally applied to non-destructive testing (NDT) for industrial product made from metal. Furthermore there are some special CT systems, which have an ability to inspect nuclear fuel assemblies or rocket motors, using high power and high energy (more than 6 MeV) pulsed X-ray source. In these case, pulsed X-ray are produced by the electron linear accelerator, and a huge number of photons with a wide energy spectrum are produced within a very short period. Consequently, it is difficult to measure the X-ray energy spectrum for such accelerator-based X-ray sources using simple spectrometry. Due to this difficulty, unexpected images and artifacts which lead to incorrect density information and dimensions of specimens cannot be avoided in CT images. For getting highly precise CT images, it is important to know the precise energy spectrum of emitted X-rays. Materials and Methods: In order to realize it we investigated a new approach utilizing the Bayesian estimation method combined with an attenuation curve measurement using step shaped attenuation material. This method was validated by precise measurement of energy spectrum from a 1 MeV electron accelerator. In this study, to extend the applicable X-ray energy range we tried to measure energy spectra of X-ray sources from 6 and 9 MeV linear accelerators by using the recently developed method. Results and Discussion: In this study, an attenuation curves are measured by using a step-shaped attenuation materials of aluminum and steel individually, and the each X-ray spectrum is reconstructed from the measured attenuation curve by the spectrum type Bayesian estimation method. Conclusion: The obtained result shows good agreement with simulated spectra, and the presently developed technique is adaptable for high energy X-ray source more than 6 MeV.

Ionisation Chamber for Measurement of Pulsed Photon Radiation Fields.

The use of pulsed photon radiation in medical, industrial and security sectors has vastly increased during the recent years. The length of pulse from different X-ray flash generators that are commonly used as either portable, battery-operated or fixed systems can be as low as a few femtoseconds. However, the majority of radiation protection instruments, especially various active electronic dosemeters, have limitations when operated in pulsed fields. This study presents measurements that were performed using the dose-integration mode of the RI-02 and Ram Ion survey metres, which are based on ventilated ionisation chamber, when exposed to different pulsed X-ray sources. An intercomparison between the results that were obtained with the survey metres and those that were obtained with thermoluminescence dosemeter, reference passive dosemeter, show good agreement (deviation lies within 10%).

Application of suppression of the borrmann effect in vibrating crystals for spatial separation of pulsed X-ray beams

The effect of suppression of the anomalous transmission of X rays due to the destruction of the system of weakly and strongly absorbing Bloch waves under ultrasound has been proposed to separate the radiation of high-intensity pulsed X-ray sources. The switching speed from the anomalous transmission mode to the zero transmission state is actually determined by only the X-ray frequency, which suggests that the switching time is several tens of nanoseconds.

An hybrid detector GEM-ASIC for 2-D soft X-ray imaging for laser produced plasma and pulsed sources

The following paper presents a new 2-D detector (`GEMpix') in the soft X-ray range, having a wide dynamic range thanks to its intrisic gain, working in charge integration mode to be used for diagnosing laser produced plasma (LPP) or X-ray pulsed sources. It is a gas detector based on the Gas Electron Multiplier (GEM) technology with a quad-medipix chip as read-out electronics. In our prototype, the substitution of semiconductor material with a gas triple-GEM allows several advantages with respect to the detectors commonly used in LPP, as X-ray CCDs and Micro Channel Plates or Image Plates. In these experiments the configuration Time-over-Threshold (ToT) has been used, to measure the total charge released to the gas and collected by each pixel, integrated over the X-ray burst duration. Intensity response and spatial resolution has been measured first in laboratory for calibration, as function of the voltage applied to the GEMs, in single photon regime with energies between 3.7 and 17 keV. Subsequently it has been tested at the ABC laser facility (ENEA, Frascati). In this case, we measured the X-rays produced when the ABC neodymium laser, with pulse of 50 J and 3 ns time width, hits plane targets of aluminum. 2-D images have been acquired by means of a pinhole configuration with magnification 1.5 and 50 μ m of spatial resolution. The results are encouraging regarding the capability of this imaging detector to work in experiments where soft X-ray emissivity varies over many orders of magnitude.

Structural Dynamics of Materials under Shock Compression Investigated with Synchrotron Radiation

Characterizing material dynamics in non-equilibrium states is a current challenge in material and physical sciences. Combining laser and X-ray pulse sources enables the material dynamics in non-equilibrium conditions to be directly monitored. In this article, we review our nanosecond time-resolved X-ray diffraction studies with 100-ps X-ray pulses from synchrotron radiation concerning the dynamics of structural phase transitions in non-equilibrium high-pressure conditions induced by laser shock compression. The time evolution of structural deformation of single crystals, polycrystals, and glass materials was investigated. In a single crystal of cadmium sulfide, the expected phase transition was not induced within 10 ns at a peak pressure of 3.92 GPa, and an over-compressed structure was formed. In a polycrystalline sample of Y2O3 stabilized tetragonal zirconia, reversible phase transitions between tetragonal and monoclinic phases occur within 20 ns under laser-induced compression and release processes at a peak pressure of 9.8 GPa. In polycrystalline bismuth, a sudden transition from Bi-I to Bi-V phase occurs within approximately 5 ns at 11 GPa, and sequential V–III–II–I phase transitions occur within 30 ns during the pressure release process. In fused silica shocked at 3.5 GPa, an intermediate-range structural change in the nonlinear elastic region was observed.

Diagnosing x-ray power and energy of tungsten wire array z-pinch with a flat spectral response x-ray diode.

Fast z-pinch is a very efficient way of converting electromagnetic energy to radiation. With an 8-10 MA current on primary test stand facility, about 1 MJ electromagnetic energy is delivered to vacuum chamber, which heats z-pinch plasma to radiate soft x-ray. To develop a pulsed high power x-ray source, we studied the applicability of diagnosing x-ray power from tungsten wire array z-pinch with a flat spectral response x-ray diode (FSR-XRD). The detector was originally developed to diagnose radiation of a hohlraum in SG-III prototype laser facility. It utilized a gold cathode XRD and a specially configured compound gold filter to yield a nearly flat spectral response in photon energy range of 0.1-4 keV. In practice, it was critical to avoid surface contamination of gold cathode. It is illustrated that an exposure of an XRD to multiple shots caused a significant change of response. Thus, in diagnosing x-ray power and energy, we used each XRD in only one shot after calibration. In a shot serial, output of FSR-XRD was compared with output of a nickel bolometer. In these shots, the outputs agreed with each other within their uncertainties which were about 12% for FSR-XRD and about 15% for bolometer. Moreover, the ratios between the FSR-XRD and the bolometer among different shots were explored. In 8 shots, the standard deviation of the ratio was 6%. It is comparable to XRD response change of 7%.

Free-electron dynamics and gain in a free-electron laser based on the laser-pumped wiggler

Relativistic electron dynamics and gain of a free-electron laser with a counter propagating linearly polarized laser wiggler embedded in a uniform guide magnetic field have been studied. This scheme enables to produce very short wavelengths via Thomson backscattering; it can be considered in principle as a source of X-ray pulses which is easily tunable and highly monochromatic. The developing of laser wiggler shortens the period lengths to micrometer level, and therefore reduces the electron beam energy required by the X-ray sources from several GeV to multi-MeV range. A fourth-order Runge–Kutta method has been employed to simulate the electron trajectories. Furthermore, the gain function of the laser-pumped FEL has been presented, in detail. Numerical solutions showed that by enhancing the cyclotron frequency (or axial magnetic field), the gain for group I orbits increased, while a gain decrement was obtained for group II orbits.

Electron trajectory simulations of time-of-flight spectrometers for core level high-energy photoelectron spectroscopy at pulsed X-ray sources

The advent of Free Electron Lasers (FELs), able to provide short (2–100fs) and intense (1033 photons/s/mm2/mrad2/0.1%bandwidth) pulses of light also in the hard X-ray regime (ℏω> 2000eV), opens new possibilities to study the ultrafast dynamics of processes, exploiting the capability of Hard X-ray Photoelectron Spectroscopy (HAXPES) to measure core-level spectra of elements with bulk sensitivity. In order to detect the intense bursts of high kinetic energy electrons generated by the X-ray pulses with an energy resolution comparable to the existing category of electron analyzers, a new class of spectrometers must be designed. We present a characterization of two different TOF spectrometers, namely one based on a retarding cylindrical lens and another one based on the spherical reflector geometry. SIMION® software has been used in order to evaluate electron trajectories of high kinetic energy electrons (5000–10,000eV) and extract transmission properties, angular acceptance and energy resolution. It resulted that while the linear system is able to accept a larger solid angle (∼50msr), the spherical mirror offers a better resolving power (around 71,000). Both analyzers are capable of a transmission above 90% within range of kinetic energies wide enough to measure the full line-shape of a core photoionization peak. Furthermore, we proved that both instruments are able to discriminate between two consecutive electron bunches having a temporal separation inferior than 220ns, which is the distance between two consecutive photon pulses at the European X-ray Free Electron Laser (EXFEL), which is currently under construction in Hamburg.

Source of rectangular X-ray pulses for studying scintillators

A pulsed X-ray source has been designed and constructed with the following parameters: X-ray tube voltage, 10–50 kV; anode current, up to 2 A; pulse duration (smooth control), 80 ns–2 μs; and leading and trailing front width, 6 ns. The source can operate in both single-pulse and pulse-train mode with a repetition frequency of up to 2 kHz. The X-ray pulse has a rectangular shape with a relative amplitude instability below 0.8%. In combination with appropriate detection system, the proposed X-ray source allows the kinetics of X-ray-induced luminescence growth and decay to be measured in a six-decimal-order dynamic range with respect to time and amplitude. Examples of X-ray-induced luminescence kinetics measured in scintillators are presented.

Development of precise energy spectrum measurement technique for high-power pulsed X-ray sources for industrial use

It is difficult to obtain an accurate energy spectrum by measurement for X-rays which are produced by linear accelerators because so many photons are emitted within a very short period and the photons have energies in a wide range. In order to solve the problem, we developed a new technique utilizing the Bayesian estimation method combined with attenuation curve measurement using a step-shaped attenuation material. We experimentally confirmed the validity of the presented technique for an X-ray computed tomography (CT) system. By using the accurate energy information of emitted X-rays obtained by the developed technique, the quality of non-destructive inspection images can be expected to be improved for industrial X-ray radiography, X-ray CT and so on, using high-power X-ray sources.

A system of X-ray visualization in the real-time mode

A system for visualizing X rays from pulsed discharges in the real-time mode using X-ray intensifying screens is described. Using the system, it is possible to record images of X-ray sources in the energy range of 1–100 keV with a spatial resolution of ∼100 μm. The proposed visualization system has been tested while optimizing the radiative characteristics of the high-current vacuum pulsed discharge. It may be employed when studying of a wide class of x-ray pulsed sources.

Radiation Dose Measurement Technique of the X-Ray Source in the Process of Stabilization

In the article the radiation burden measurement technique of the X-ray source in the process of stabilization is described. The possibility of using this technique for the dose rate determination from the pulsed X-ray source is presented. The measurement technique approbation results at the pulsed X-ray source RAP-160-5 using thermoluminescent dosimeters DTL-02 are shown.

Dose Rate Spatial Distribution Produced by the Pulsed X-Ray Source in the Radiographic Examination

In the article the dose rate measurement technique of the pulsed X-ray source RAP-160-5 is presented. The examples of the dose rate spatial distribution for the different pulsed X-ray tube parameters at the different distance between the pulsed X-ray source focus and the detector are demonstrated. The recommendations for the radiation dose optimization to the objects under investigation from the different distance between the pulsed X-ray source focus and the detector are proposed.

ChemInform Abstract: Recent Advances on Ultrafast X‐Ray Spectroscopy in the Chemical Sciences

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