High-energy X-ray Radiography Research Articles

Intrinsic scintillation performance & europium concentration effects in RbSr2I5 and RbSr2Br5 scintillators

Scintillators play crucial roles in homeland security applications like gamma ray spectroscopy and high energy X-ray radiography. For promising new scintillators, fine-tuning the luminescent dopant concentration is one avenue to further improve their performance and tailor their properties. In this work, the effects of europium dopant concentrations on the crystal growth, luminescence and scintillation properties of RbSr2Br5 and RbSr2I5 crystals was investigated. Nine transparent 7 mm diameter single crystals were grown via the Vertical Bridgman method. The optical band gap of RbSr2Br5 was 5.9 eV and that of RbSr2I5 was 4.7 eV. High scintillation performance was achieved with a relatively low europium concentration of 1 mol%. For both RbSr2Br5:Eu and RbSr2I5:Eu crystals, light yield of 60–90,000 ph/MeV, energy resolution 2.8–4.0 % at 662 keV, and X-ray afterglow 0.79–1.5 % at 2 ms were obtained.

Laser-driven double shock loading and diagnosis technology for material ejection from surface

The physics of shock-induced ejection is a crucial phenomenon in the field of shock compression science and technology. Limited by loading methods, the previous research primarily focused on the physics of ejecta induced by single shockwave, with few data available on multiple shockwave loading conditions. To solve this problem, we proposed a double shockwave production method based on the high-intensity laser facility, which allows the interval time between the shock waves to be adjusted in the nanosecond to microsecond timescale. Meanwhile, we applied loading techniques to study the ejection behavior of metal tin and integrated photonic doppler velocimetry and high-energy x-ray radiography technology to observe the ejection process. By comparing the experimental results for single and double shockwave, the multiple shock-induced ejection features have been clearly confirmed. Our experimental results provide valuable insight into the behavior of ejecta under multiple shockwave loading conditions, which is of great significance for deepening our understanding of the ejection mechanism.

Enhancement of high energy X-ray radiography using compound parabolic concentrator targets

We report an increase in MeV energy bremsstrahlung x-ray production using compound parabolic concentrators (CPC) compared to flat solid targets during relativistic laser-plasma experiments on a 140 J, 150 fs laser system using an f/40 focusing optic. CPC enhanced targets show a >3× increase in high energy x-ray production over planar foil targets. This enhancement in x-ray energy spectra shows a direct improvement in the radiography of an image quality indicator (IQI) object with a 20 g/cm2 areal density.

Uncertainty Quantification of Density Reconstruction Using MCMC Method in High-Energy X-ray Radiography

Uncertainty Quantification of Density Reconstruction Using MCMC Method in High-Energy X-ray Radiography

Image restoration of high-energy X-ray radiography with a scintillator blur model

High-energy X-ray radiographic image restoration is performed using a simulated radiation point spread function and an experimentally derived optical point spread function. It is shown that a robust method for removal of thick monolithic scintillator blur can be determined through independent examination of the blur components. We show that the scintillator blur for a 20 MeV end-point X-ray beam and 20 mm thick LYSO scintillator contributes significantly to the system blur. It is also shown that the optical scatter in the monolithic crystal degrades the low-frequency response of the system. The use of a simulated point spread function for image restoration using deconvolution provides a simple method for image restoration, thereby enhancing feature identification and areal density reconstruction.

Experimental technique for dynamic fragmentation of materials via indirect drive by high-intensity laser

High intensity laser is an efficient method for shock generator to study the dynamic fragmentation of materials, in which the direct drive is widely utilized. The continuum phase plate is used for smoothing the focal spot of the laser, but the loading region is usually smaller than the designed value. In this work, we study an experimental technique for investigating the dynamic fragmentation of metal via indirectly driving a high-intensity laser. Firstly, the radiation distributions on the sample for four different hohlraums each with a diameter of 2 mm but different length are simulated via the IRAD software, in which the proper hohlraum with a diameter of 2 mm and a height of 2 mm is selected for the experiments. Secondly, the peak temperatures and radiation waves under different laser energy and pulse durations are measured. The peak temperature decreases simultaneously as the laser energy decreases. In addition, the loading shock waves under a peak temperature of 140 eV and different radiation waves are estimated via the hydrodynamic simulation. It is revealed that a peak pressure of several tens of gigapascals is acquired and the peak pressure is greatly increased when the 10 μm CH layer is placed on the sample. In the end, the dynamic fragmentation process via indirect drive is investigated by using the high energy X-ray radiography and photonic Doppler velocimetry. The radiograph is a snapshot at 600 ns and shows a typical result of the spall process. The first layer is measured to be 0.06 mm thick and 0.3 mm away from the unperturbed free surface. It is also exhibited that the hohlraum is expanded to a large extent but is not broken up. The jump-up velocity and time of spall are measured to be 0.65 km/s and 131 ns, respectively. The average velocity of the first layer is estimated to be (0.63 ± 0.1) km/s, obtained via the distance of 0.3 mm divided by the time difference of 469 ns (600 ns minus 131 ns). The one-dimensional loading region is 2 mm, and the flatness is better than 5 %. This work provides a reference for designing new hohlraum, shock wave loading technique and dynamic fragmentation process.

Modified floating-zone crystal growth of Mg4Ta2O9 and its scintillation performance

Rods of single crystal MgTaO9 were produced free of macroscopic defects and their scintillation properties including afterglow were measured. The compound characteristics make it a candidate for high energy X-ray radiography applications.

High-energy X-ray radiography investigation on the ejecta physics of laser shock-loaded tin

This study is devoted to the high-energy X-ray radiography investigation on the ejecta physics of laser shock-loaded tin. The ejecta were generated via laser shock loaded tin under sequential shock-breakout pressures by high-power nanosecond lasers. A high-energy X-ray (50∼200keV) source was created to radiograph the high dense ejecta. Due to its strong penetration, high-quality radiograph images were obtained with detailed inner information and topology structure of ejecta. The areal density distribution and total mass of ejecta were further inferred. It was found that the ejecta from laser shock-loaded tin under sequential pressures show obvious difference in density distribution between the samples in a solid state and in a melt-on-release state. In addition, the total mass of ejecta was demonstrated to increase sharply when the breakout pressure is larger than the onset of melt-on-release for tin. Such increase inferred a solid-liquid phase transition of ejecta production mechanism.

High-energy X-ray radiography of laser shock loaded metal dynamic fragmentation using high-intensity short-pulse laser.

The dynamic fragmentation of shock-loaded high-Z metal is of considerable importance for both basic and applied science. The areal density and mass-velocity distribution of dynamic fragmentation are crucial factors in understanding this issue. Experimental methods, such as pulsed X-ray radiography and proton radiography, have been utilized to obtain information on such factors; however, they are restricted to a complex device, and the spatial resolution is in the order of 100 μm. In this work, we present the high-quality radiography of the dynamic fragmentation of laser shock-loaded tin, with good two-dimensional (2D) spatial resolution. Dynamic fragmentation is generated via high-intensity ns-laser shock-loaded tin. A high-energy X-ray source in the 50-200 keV range is realized by the interaction of a high-intensity ps-pulse with an Au microwire target, attached to a low-Z substrate material. A high 2D resolution of 12 μm is achieved by point-projection radiography. The dynamic-fragmentation radiography is clear, and the signal-to-noise ratio is sufficiently high for a single-shot experiment. This unique technique has potential application in high-energy density experiments.

Point Spread Function Estimation in X-Ray Imaging with Partially Collapsed Gibbs Sampling

The point spread function (PSF) of a translation invariant imaging system is its impulse response, which cannot always be measured directly. This is the case in high-energy X-ray radiography, and the PSF must be estimated from images of calibration objects indirectly related to the impulse response. When the PSF is assumed to have radial symmetry, it can be estimated from an image of an opaque straight edge. We use a nonparametric Bayesian approach, where the prior probability density for the PSF is modeled as a Gaussian Markov random field and radial symmetry is incorporated in a novel way. Markov chain Monte Carlo posterior estimation is carried out by adapting a recently developed improvement to the Gibbs sampling algorithm, referred to as partially collapsed Gibbs sampling. Moreover, the algorithm we present is proven to satisfy invariance with respect to the target density. Finally, we demonstrate the efficacy of these methods on radiographic data obtained from a high-energy X-ray diagnostic system at the U. S. Department of Energy's Nevada National Security Site.

Detector characterization and electron effect for laser-driven high energy X-ray imaging

High energy X-ray sources based on laser-wakefield accelerated electron beams have several important advantages, including high photon energy and small source size, and have many important applications such as high resolution radiography in non-destructive testing. Firstly, the thickness of electron converter is optimized with the targets Ta, W and Pb each with an optimal thickness of 2 mm. We calibrate the intrinsic spatial resolution of CsI needle-like scintillation screen, bismuth germanium oxide (BGO) scintillation array and DRZ scintillation screen with an X-ray tube. And the spatial resolution of CsI needle-like scintillation screen is as high as 8.7 lp/mm. The energy deposition responses of these three detectors to high X-ray are also simulated. Experiments show that the features of a two-layer object can be resolved up to an area density of 33.0 g/cm2 by using the high X-ray source generated by injecting laser-wakefield accelerated electron beam into a Ta convertor target. Experiment that compares X-ray radiography, mixed radiography of X-ray and electron, and electron radiography, is also carried out. Since low X-ray yield and low detection efficiency are two serious problems in high energy X-ray radiography based on laser-wakefield accelerated electron beams, we propose and prove a method of improving image signal intensity greatly at the cost of image contrast by adopting the mixed radiography of X-ray and electron.

Bayesian Abel Inversion in Quantitative X-Ray Radiography

A common image formation process in high-energy X-ray radiography is to have a pulsed power source that emits X-rays through a scene, a scintillator that absorbs X-rays and fluoresces in the visible spectrum in response to the absorbed photons, and a charge-coupled device camera that images the visible light emitted from the scintillator. The intensity image is related to areal density, and, for an object that is radially symmetric about a central axis, the inverse Abel transform then gives the object's volumetric density. Two of the primary drawbacks to classical variational methods for Abel inversion are their sensitivity to the type and scale of regularization chosen and the lack of natural methods for quantifying the uncertainties associated with the reconstructions. In this work we cast the Abel inversion problem within a statistical framework in order to compute volumetric object densities from X-ray radiographs and to quantify uncertainties in the reconstruction. A hierarchical Bayesian model is developed with a likelihood based on a Gaussian noise model and with priors placed on the unknown density profile, the prior precision matrix, and two scale parameters. This allows the data to drive the localization of features in the reconstruction and results in a joint posterior distribution for the unknown density profile, the prior parameters, and the spatial structure of the precision matrix. Results of the density reconstructions and pointwise uncertainty estimates are presented for both synthetic signals and real data from a U.S. Department of Energy X-ray imaging facility.

Determination of the blur size of a radiographic system from density reconstruction

Blurring is a serious problem in hydrotest experiments with high-energy X-ray radiography. We propose a new method that determines the blur size of a radiographic system from density reconstruction. First, we test the method on a simulated image whose blur is known in advance. Then, we apply the method to obtain the blur size of a realistic radiographic system from an experimental image produced by the system. Finally, we verify the obtained blur size via a radiographic experiment on a step object.

Decreasing the scatter effect in density reconstruction in high-energy x-ray radiography

Scatter is a serious problem in hydro-test with high-energy x-ray radiography and makes it difficult to reconstruct density distributions from radiographic images. A precise method to decrease the scatter impact is proposed. In this method, the shape of scatter distribution is obtained by Monte Carlo (MC) simulation and the overall scatter scale is determined by the mass constrain. We then applied the method to reconstruct a Computer-synthesized image of the French Test Object (FTO). The results show that our method works well and the scatter effect is removed almost completely. This method is a proper way to improve the diagnostic ability of the high-energy x-ray facility on hydro-test and weapon stockpile greatly.

Performance Study of the Anti-Scatter Grid for Sub-Megavolt X-Ray Flash Radiography

In the field of the flash radiography scattering is one of the most important affecting factors in determining the object information. A state-of-the-art optical component called anti-scatter grid has been used in high energy X-ray radiography. But the application for such kind of module in sub-megavolt (100 keV ~ 1MeV) flash radiography has not been mentioned yet. Recently our group has designed a new grid which was different with the products either in high energy X-ray radiography or in low energy mammography. The grid was manufactured and then tested in a 450 keV flash radiography source. The experimental results indicated that the grid’s anti-scatter capability was superexcellent. The Monte Carlo simulation also confirmed the experimental conclusion and the scattered to primary ratios with and without the grid were evaluated quantificationally.

基于全变分正则化的高能闪光照相消模糊图像重建算法

基于全变分正则化的高能闪光照相消模糊图像重建算法

Monte Carlo simulation for bremsstrahlung and photoneutron yields in high-energy x-ray radiography

This paper reports on the results of calculations using a Monte Carlo code (MCNP5) to study the properties of photons, electrons and photoneutrons obtained in the converted target and their transportations in x-ray radiography. A comparison between measurements and calculations for bremsstrahlung and photoneutrons is presented. The radio-graphic rule and the effect of the collimator on the image are studied with the experimental model. The results provide exact parameters for the optimal design of radiographic layout and shielding systems.

Preventing the Importation of Illicit Nuclear Materials in Shipping Containers

We develop a mathematical model to find the optimal inspection strategy for detecting a nuclear weapon (or nuclear material to make a weapon) from being smuggled into the United States in a shipping container, subject to constraints of port congestion and an overall budget. We consider an 11-layer security system consisting of shipper certification, container seals, and a targeting software system, followed by passive (neutron and gamma), active (gamma radiography), and manual testing at overseas and domestic ports. Currently implemented policies achieve a low detection probability, and improved security requires passive and active testing of trusted containers and manually opening containers that cannot be penetrated by radiography. The annual cost of achieving a high detection probability of a plutonium weapon using existing equipment in traditional ways is roughly several billion dollars if testing is done domestically, and is approximately five times higher if testing is performed overseas. Our results suggest that employing high-energy x-ray radiography and elongating the passive neutron tests at overseas ports may provide significant cost savings, and several developing technologies, radiation sensors inside containers and tamper-resistant electronic seals, should be pursued aggressively. Further effort is critically needed to develop a practical neutron interrogation scheme that reliably detects moderately shielded, highly enriched uranium.

On the Effect of Lead and Fluorometallic Intensifying Screens in High Energy X-ray Radiography

On the Effect of Lead and Fluorometallic Intensifying Screens in High Energy X-ray Radiography