Gamma-ray Radiography Research Articles

Virtual source approach for maximizing resolution in high-penetration gamma-ray imaging

High-energy gamma-ray radiography has exceptional penetration ability and has become an indispensable nondestructive testing (NDT) tool in various fields. For high-energy photons, point projection radiography is almost the only feasible imaging method, and its spatial resolution is primarily constrained by the size of the gamma-ray source. In conventional industrial applications, gamma-ray sources are commonly based on electron beams driven by accelerators, utilizing the process of bremsstrahlung radiation. The size of the gamma-ray source is dependent on the dimensional characteristics of the electron beam. Extensive research has been conducted on various advanced accelerator technologies that have the potential to greatly improve spatial resolution in NDT. In our investigation of laser-driven gamma-ray sources, a spatial resolution of about 90 µm is achieved when the areal density of the penetrated object is 120 g/cm2. A virtual source approach is proposed to optimize the size of the gamma-ray source used for imaging, with the aim of maximizing spatial resolution. In this virtual source approach, the gamma ray can be considered as being emitted from a virtual source within the convertor, where the equivalent gamma-ray source size in imaging is much smaller than the actual emission area. On the basis of Monte Carlo simulations, we derive a set of evaluation formulas for virtual source scale and gamma-ray emission angle. Under optimal conditions, the virtual source size can be as small as 15 µm, which can significantly improve the spatial resolution of high-penetration imaging to less than 50 µm.

Radiographic testing of 3D-printed thermoplastics using Am-241 as a gamma-ray source

The industrial production of 3D printing is known as additive manufacturing (AM), in which a computer controls the process of producing 3D objects. Although x-ray computed radiography (XCT) is extensively used in the quality control and testing of additive manufacturing products, the gamma-ray radiography capabilities for these applications still need to be investigated. This study aimed to evaluate the performance of gamma-ray radiography using americium-241 (Am-241) as the gamma source. Here, we inspected fused deposition three-dimensional (3D) modeling products produced from polylactic acid (PLA) as thermoplastic samples. Radiographic testing of 3D-printed thermoplastic samples was performed using Monte Carlo simulations and validated by experimental studies. We used Am-241 (gamma-ray source) to conduct simulations and experiments investigations; two simulations were used: one by using 59.6 keV energy of gamma-ray and the other using all gamma-ray energies, including 16.96 keV, 26.3446 keV% 2.31 up to 662.40 keV. Also, we performed the x-ray radiography test to be used as a standard. The results showed that the defect detectability in the 3D-printed PLA samples using Am-241 as a gamma-ray source is comparable to that of x-ray results. This study concluded that the Am-241 could be used as the gamma-ray source to perform the radiography test for the products produced by 3D-printed thermoplastics.

Investigate shielding of standard materials and glass for stopping 662 KeV gamma ray penetrations

Calculations on shielding are required for the building of a gamma ray radiography exposure room to ensure worker exposure to radiation. A measurement used to evaluate the radiation diffusive and absorption characteristics of a medium is the linear attenuation coefficient ( ). Despite the fact that, as radiation moves through a medium, its absorption is influenced by the wavelength of the radiation as well as the thickness and composition of the medium, the linear absorption coefficient is crucial in the interaction of radiation with matter. This research uses a variety of materials as a shield for a gamma radiation source of emitted by Cs-137. The results obtained using a gamma source with a scintillation counter showed that the Half Value Thickness (HVT) of glass and aluminum were 3.57 cm, and 3.39 cm while for standard materials (concrete, iron, and lead) were 2.98 cm, 1.195 cm, and 0.58 cm respectively.

Characterization of sub-picosecond laser-produced fast electrons by modeling angularly resolved bremsstrahlung measurements with 3D hybrid particle-in-cell code

Hard x-rays produced by intense laser-produced fast electrons interacting with solids are a vital source for producing radiographs of high-density objects and implosion cores for inertial confinement fusion. Accurate calculation of hard x-ray sources requires a three-dimensional (3D) simulation geometry that fully models the electron transport dynamics, including electron recirculation and the generation of absolute photon yields. To date, 3D simulations of laser-produced bremsstrahlung photons over tens of picoseconds and code benchmarking have not been performed definitively. In this study, we characterize sub-picosecond laser-produced fast electrons by modeling angularly resolved bremsstrahlung measurements for refluxing and non-refluxing targets using the 3D hybrid particle-in-cell (PIC), Large Scale Plasma code. Bremsstrahlung radiation and escaped electron data were obtained by focusing a 50-TW Leopard laser (15 J, 0.35 ps, 2 × 1019 W/cm2) on a 100-μm-thick Cu foil and a Cu with a large plastic backing (Cu–CH target). Data for both the Cu and Cu–CH targets were reproduced for simulations with a given set of electron parameters. Comparison of the simulations revealed that the hard x-ray emission from the Cu target was significantly longer in duration than that from the Cu–CH target. The benchmarked hybrid PIC code could prove to be a powerful tool in the design and optimization of time- and angular-dependent bremsstrahlung sources for flash x-ray and gamma-ray radiography.

Exposure Determination in Gamma-Ray Radiography for Mammography Applications

Exposure Determination in Gamma-Ray Radiography for Mammography Applications

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 >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.

Mathematical Behavior of Optical Density of γ-Ray Radiography Images of Steel Pipes

The purpose of this article is to determine the mathematical function of the optical behavior of radiographic films/images produced by gamma-ray radiography of the steel pipes. In order to achieve this goal, we used realistic films for welding tests on the oil and gas pipelines in the operational areas. Eight films were selected in each, three sections including the base metal, weld line, and defects were carefully examined. First, the best film was selected and more than 40 probability functions were fitted on its data. Among the fitted probability functions, 13 functions were selected from a condition of R-sq ≥ 0.95. Eventually, these 13 functions were applied to the data of all available films for a better comparison. Furthermore, a new function was proposed by the authors, which showed that the fitting was based on the results. The new proposed function, fulfilled not only the best R-sq, but also the most flexibility in the case of scattered data.

Combined gamma-ray and energy-selective neutron radiography at CSNS

Combined photon and neutron radiography can integrate merits of X/gamma-ray radiography and energy-selective neutron radiography and has the potential of simultaneously visualizing objects composed of high-Z materials, low-Z materials and particular isotopes that resonantly absorb neutrons at certain energies. Intense pulsed gamma bursts and wide energy spectrum neutrons at spallation sources provide a unique opportunity to perform such combined radiography research. We present the results of the combined radiography experiments performed at the back-streaming white neutron (back-n) beamline at China Spallation Neutron Source (CSNS). Gamma-ray and energy-selective neutron radiographic images of multi-element samples were taken by an ICCD camera coupled with scintillators using the time of flight (TOF) technique. High-Z (Pb, Au, W, Ta, et al.) components were visualized with the intense gamma-ray bursts. The low-Z (10B) component was confirmed with varied image contrast when neutrons with varied energies were selected. The specific elements (natIn, 197Au and natW) were identified with neutrons at corresponding resonant energies. The experimental results prove the potential for simultaneously visualizing and identifying high-Z materials, low-Z materials and particular nuclides via combined X-ray radiography and energy-selective neutron radiography.

MeV photon imaging with robotic sample positioning at a research reactor

This paper summarizes the development and demonstration of an X-ray and gamma-ray radiography capability using a TRIGA MARK-II reactor. Photons are a combination of Bremsstrahlung X-rays and gamma rays from fission and radioactive decay. The energy spectrum of the facility was analyzed with a NaI(Tl) scintillator detector. A digital X-ray camera for use with MeV-range photons images a duplex wire-type penetrameter to analyze unsharpness and spatial resolution. An industrial manipulator precisely positions the sample, which allows objects to have larger dimensions than the detector’s field-of-view. Future work includes performing computed tomography to create 3-dimensional representations of objects.

Micro-spot gamma-ray generation based on laser wakefield acceleration

The radiography of gamma-ray is one of the most important non-destructive testing in many fields. However, the spot size is always in millimeter scale for the generation of gamma-ray by conventional way. As the development of laser wakefield acceleration, the electron beam with small divergence and spot size can be generated easily in the experiment by tens of terawatt ultra-short laser pulse. Based on this electron beam, gamma-ray with micro spot size is generated and the properties are measured and tested in detail experimentally. The experiment demonstrates that the spot size of this gamma-ray is always smaller than 200 μm, no matter the conversion target thickness, and can be as small as about 40 μm when the conversion target thickness of 0.2 mm is used. The spatial resolution of this gamma-ray is much better than 2.5 LP/mm, the fitting temperature (which is relative to the average energy of gamma-ray) is between 5 MeV and 8 MeV, and the maximum yield per shot of the gamma-ray can be up to 9.1 × 109 photons (energy higher than 1 MeV). High-resolution radiography shows that the areal density of the gamma-ray radiography can be up to 51.3 g/cm2 (stainless steel thickness equivalent is about 6.5 cm). Such micro-spot gamma-ray can play an important role in the high-resolution radiography of high areal density objects.

Digital neutron and gamma-ray radiography in high radiation environments with an MCP/Timepix detector

The radiation levels from used nuclear fuel make their post irradiation examination very difficult. Handling material removed from assemblies is almost exclusively performed inside shielded hot cells. Neutron radiography provides a non-destructive option for examining the internal structure, location and integrity of irradiated fuel. This paper addresses the performance and stability of a neutron imaging detector comprised of microchannel plates (MCPs) and a Timepix readout in gamma and neutron radiation environments. The detector is being considered as an alternative to the currently used activation foils and photographic film measurement techniques. The MCP/Timepix detector was used in neutron radiography experiment on a beam line at the Neutron Radiography Reactor (NRAD) at Idaho National Laboratory (INL). The detector was installed ∼17.5 m from the reactor core with a line of sight view to the core, which results in a fast and epithermal neutron spectrum as well as high intensity gamma radiation. The gamma-ray dose rate in the beam line was 812 mSv/hr. Complementary measurements were made using 137Cs and 60Co isotopic sources at gamma dose rates in excess of 6 Sv/hr. The detector functioned normally over several hours in this environment. These conditions are comparable to planned radiography of irradiated nuclear fuel assemblies. Experimental results using ASTM sensitivity and beam purity indicators suggest that a spatial resolution of <100 μm may be possible in neutron radiographic measurements using this detector for studies of irradiated nuclear fuel. Potential radiographic and tomographic applications are discussed. The results of present experiments are not limited to the studies of irradiated fuel assemblies, but rather are relevant to any experiment where imaging needs to be performed in a high radiation environment.

Channeling and radiation experiments at SLAC

Over the last years, a SLAC-Aarhus-Ferrara-CalPoly collaboration (augmented by members of ANL and MIT) has performed channeling experiments using bent silicon crystals at the SLAC End Station A Test Beam as well as the FACET accelerator test facility. These experiments have revealed a remarkable channeling efficiency of about 24% under our conditions, as well as shown the dechanneling rate to be independent of the beam energy; an unexpected result. Volume reflection appears to be even more efficient with almost the whole beam taking part in the reflection process. In our most recent experiment we have attempted to measure the spectrum of channeling and volume-reflection gamma radiation. The goal of this series of experiments is to develop a crystalline undulator capable of producing narrow-band gamma rays with electron beams. Such a device could have applications in gamma-ray radiography as well as spectroscopic applications.

Characterization of Weldments Defects through Non Destructive Evaluation Techniques

Background/Object: Non-destructive Testing (NDT) methods are valuable tools in quality assurance of weldments in engineering and technology. The objective of this paper is to evaluate the structural health monitoring of the weldments through NDT methods. Methods/Analysis: The samples taken for these studies are extensively used in Aerospace and industrial applications. The dimensions of fabricated samples of stainless steel and mild steel is 300 mm × 180 mm × 10 mm, D3 tool steel is 180 mm × 150 mm × 25 mm, Aluminum is 150 mm × 120 mm × 10 mm and Titanium is 160 mm × 60 mm × 2 mm. These samples are subjected to Gas Tungsten Arc welding (GTAW) during welding artificial defects are incorporation by altering the weld parameters. The profile of weld defects is studied by using basic Non-Destructive Testing techniques. Findings: Defects which are open to surface and subsurface defects up to 6mm depth are detected by Visual Inspection (VI), Liquid Penetrant Test (LP) and Magnetic Particle Inspection (MPI) techniques. Ultrasonic - B scan NDT technique is adapted for study of thickness profile of weld region of weldments found distinct result in aluminum weldments. Orientation and Internal of defects of the weldments were detected by Gamma ray Radiography and Ultrasonic Testing methods found forging material inclusion in SS material, Aluminum weldments. Application/Improvements: These evaluation studies through Nondestructive Testing techniques are much useful for structural health monitoring of the weldments.

Vehicle and Cargo Scanning for Contraband

There is a need to inspect vehicles and their contents for Special Nuclear Material (SNM) and general contraband. The most widely used technology for scanning vehicles, ranging from vans and trucks to railcars, is gamma-ray and X-ray radiography. New technologies are required for higher penetration to reduce insufficient penetration alarms, for improved image quality and material discrimination to increase detection at high throughput and to enable scanning fast-moving trains. In most cases, the scanning footprint, which includes the radiation exclusion zone, must be small due to the limited space available at the inspection sites. Some of these conflicting requirements have been addressed by employing adaptive intensity and/or energy modulation of the X-ray source. Any alarms produced by these primary systems need to be cleared or confirmed to eliminate labor-intensive manual inspection. Various technologies have been proposed and used for secondary inspection, mainly based on the detection of fission signatures. Such systems would preferentially require minimal infrastructure and cost would be kept reasonably commensurate with the performance improvements to allow for wide deployment. The Domestic Nuclear Detection Office (DNDO) has performed tests of some of these systems to determine the envelope of the various technologies. Selected results with primary systems, and examples of potential system improvements are presented.

Application of gamma-ray radiography and gravimetric measurements after accelerated corrosion tests of steel embedded in mortar

The accelerated corrosion by the impressed current technique is widely used in studies of concrete durability since it has the advantage that tests can be carried out within reasonable periods of time. In the present work the relationship between the applied current density and the resulting damage on the reinforcing steel, by applying optical microscopy, scanning electron microscopy, gamma-ray radiography and gravimetric measurements, was studied by means of the implementation of accelerated corrosion tests on reinforced mortar. The results show that the efficiency of the applied current is between 1 and 77%, regardless of the applied current density, the water/cement ratio and the mortar cover depth of the specimens. The results show the applicability of the gamma-ray radiography technique to detect localized corrosion of steel rebars in laboratory specimens.

An industrial radiography exposure device based on measurement of transmitted gamma-ray intensity

In film radiography, underexposure and overexposure may happen particularly when lacking information of specimen material and hollowness. This paper describes a method and a device for determining exposure in industrial gamma-ray radiography based on quick measurement of transmitted gamma-ray intensity with a small detector. Application software was developed for Android mobile phone to remotely control the device and to display counting data via Bluetooth communication. Prior to film exposure, the device is placed behind a specimen to measure transmitted intensity which is inversely proportional to the exposure. Unlike in using the conventional exposure curve, correction factors for source decay, source-to- film distance, specimen thickness and kind of material are not needed. The developed technique and device make radiographic process economic, convenient and more reliable.

Fabrication and evaluation of rare-earth-bearing fuel slugs for sodium-cooled fast reactors

Separation of rare-earth (RE) elements from minor actinides is difficult in pyroprocessing, especially for light REs (e.g., Nd, Ce, Pr, and La). Herein, U–10 wt%Zr fuel slugs containing 0, 3, and 7 wt%RE (RE: a rare-earth alloy comprising 53 % Nd, 25 % Ce, 16 % Pr, and 6 % La by weight) were prepared by gravity casting. Their casting soundness was characterized by gamma-ray radiography and immersion density measurement, while their microstructures and compositions were analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Their actual compositions and impurities were confirmed using inductively coupled plasma atomic emission spectrometry. The compatibility of casting components and recovery of radioactive materials were evaluated based on the RE content.

Fabrication of uranium alloy fuel slug for sodium-cooled fast reactor by injection casting

Metal fuel slugs of U–Zr alloys for a sodium-cooled fast reactor (SFR) have been fabricated using an injection casting method. However, casting alloys containing volatile radioactive constituents such as Am can cause problems in a conventional injection casting method. Therefore, in this study, several injection-casting methods were applied to evaluate the volatility of the metal-fuel elements and control the transport of volatile elements. Mn was selected as a volatile surrogate alloy since it possesses a total vapor pressure equivalent to that of minor actinide-bearing fuels for SFRs. U–10 wt% Zr and U–10 wt% Zr–5 wt% Mn metal fuels were prepared, and the casting processes were evaluated. The casting soundness of the fuel slugs was characterized by gamma-ray radiography and immersion density measurements. Inductively coupled plasma atomic emission spectroscopy was used to determine the chemical composition of fuel slugs. Fuel losses after casting were also evaluated according to the casting conditions.

Development of a new casting method to fabricate U–Zr alloy containing minor actinides

Metal fuel slugs of U–Zr alloys for a sodium-cooled fast reactor (SFR) have conventionally been fabricated using an injection casting method. However, casting alloys containing volatile radioactive constituents, such as Am, are problematic in a conventional injection casting method. As an alternative fabrication method, low pressure gravity casting has been developed. Casting soundness, microstructural characteristics, alloying composition, density, and fuel losses were evaluated for the following as-cast fuel slugs: U–10 wt% Zr, U–10 wt% Zr–5 wt% RE, and U–10 wt% Zr–5 wt% RE–5 wt% Mn. The U and Zr contents were uniform throughout the matrix, and impurities such as oxyen, carbon, and nitrogen satisfied the specification of total impurities less than 2,000 ppm. The appearance of the fuel slugs was generally sound, and the internal integrity was shown to be satisfactory based on gamma-ray radiography. In a volatile surrogate casting test, the U–Zr–RE–Mn fuel slug showed that nearly all of the manganese was retained when casting was done under an inert atmosphere.

Feasibility study of gamma-ray medical radiography

This research explores the feasibility of using gamma-ray radiography in medical imaging. We will show that gamma-ray medical radiography has the potential to provide alternative diagnostic medical information to X-ray radiography. Approximately one Ci Am-241 radioactive source which emits mono-energetic 59.5keV gamma rays was used. Several factors that influence the feasibility of this study were tested. They were the radiation source uniformity, image uniformity, and image quality parameters such as contrast, noise, and spatial resolution. In addition, several gamma-ray and X-ray images were acquired using humanoid phantoms. These images were recorded on computed radiography image receptors and displayed on a standard monitor. Visual assessments of these images were then conducted.The Am-241 radioactive source provided relatively uniform radiation exposure and images. Image noise and image contrast were mainly dependent on the exposure time and source size, whereas spatial resolution was dependent on source size and magnification factor. The gamma-ray humanoid phantom images were of lower quality than the X-ray images mainly due to the low radioactivity used and not enough exposure time. Nevertheless, the gamma-ray images displayed most of the main structures contained in the humanoid phantoms. Higher exposure rates and thus lower exposure times were estimated for different pure Am-241 source sizes that are hypothesized to provide high quality images similar to X-ray images. For instance, a 10mm source size of pure Am-241 with 7s exposure time should produce images similar in contrast and noise to X-ray images. This research paves the way for the production and usage of a highly radioactive Am-241 source with the potential to lead to the feasibility of acceptable quality medical gamma-ray radiography.