Compton Backscatter Research Articles

Deep learning based Compton backscatter imaging with scattered X-ray spectrum data: A Monte Carlo study

Compton backscatter imaging (CBI) is a non-destructive testing (NDT) technique with the Compton effect. In CBI, the radiation source and detector are positioned on the same side of the object, which means that the imaging is almost not limited by the size of the object. The characteristic of single-sided imaging gives CBI substantial potential for applications in specific scenarios. In field archaeology, CBI can rapidly acquire subsurface images with the millimeter-level resolution, effectively enhancing archaeological excavation efficiency while better protecting artifacts. Therefore, CBI offers substantial potential in archaeological excavation. To address the problem of severe noise in CBI, we employed a scintillation detector to receive backscattered X-rays. Transformers directly reconstruct multi-channel projections to swiftly and accurately obtain precise reconstruction images. Monte Carlo simulation experiments confirm this method’s suitability for detecting a variety of common archaeological materials. Experimental results indicate that compared with count mode, multi-channel projections can effectively improve the reconstruction quality of CBI. Moreover, CBI can clearly image various materials of buried artifacts, proving the method’s versatility and practical value in NDT field.

Characterizing Modulation Transform Functions for varying Zeff materials

Compton Backscatter Imaging (CBI) is a decades old approach to imaging surfaces where positioning of a detector and x-ray source for transmission imaging is either not possible or convenient. For that reason, it has been explored and utilized in areas of explosive detection and security applications, railway infrastructure integrity, and aerospace safety. Within these applications, much of the focus is on resolution for specific signatures within the target medium, particularly voids that indicate decreased structural integrity. The purpose of this research is to characterize the Modulation Transfer Function (MTF) signature of plastic, lead, steel, aluminum, and copper. MTF contrast analysis yields greater results in image clarity and post processing when compared to altering the image capture alone. Doing so would allow researchers to configure scanning equipment to detect key elements specific to CBI imaging of potential explosive devices. While past research has focused on an explosive penalty or contraband, the goal for this research is to target components of a device like the wiring or power source.

Diagnosis of Radial Deformation and Axial Displacement Faults in Power Transformer Windings using X-ray and Compton Backscatter Imaging

Continuous and uninterrupted transmission and distribution of electrical energy is highly dependent on the flawless operation of power transformers. Failure of these critical components can lead to network power interruptions and consequently have severe detrimental consequences. Therefore, timely detection and diagnosis of power transformer faults is crucial not only to prevent the escalation of faults but also to minimize repair and maintenance costs. Conventional methods for inspecting windings faults have limitations such as the need to take the transformer out of service, unreliable results, and the addition of auxiliary devices inside the transformer, such as dielectric windows. In contrast, the proposed method in this paper utilizes a Compton Backscatter Imaging (CBI) or X-Ray Transmission (XRT) device located outside the transformer, eliminating the need for any additional equipment. This enables online scanning of any number of transformers to assess their health status and identify the type, extent, and progression of potential internal faults. Experimental results demonstrate the feasibility of the proposed method for detecting radial deformation and axial displacement and disk space variations faults of varying magnitudes and locations in both high-voltage and low-voltage windings of power transformers.

Improved cement sheath thickness measurement and its application in cement sheath variation monitoring

Monitoring cement sheath thickness by the logging tool that utilizes Am–Be neutron generator as radiation source is crucial for the secure exploitation of oil and gas fields. Generally, a positive source distance probe is adopted to evaluate the cement sheath thickness by recording single energy window count, but the measurement result is greatly impacted by the working state of instrument. To get accurate changes about the thickness of cement sheath, this paper proposes a dual energy window combination method by photoelectric window and Compton backscatter window based on the scattering and attenuation theory of gamma ray in the medium. Subsequently, the relationship between the counting ratio of low window to high energy window and the thickness of cement sheath is established. By adjusting MCNP model settings, it can be concluded that the borehole fluid, the density of cement sheath, and the thickness of casing effects on the counting ratio of energy window A to energy window C for measuring cement sheath thickness can be disregarded. Besides, high-density formation and corrected borehole diameter are beneficial for evaluating the cement sheath thickness. According to these results, the simulation example shows that the thickness calculation error of the method at the overall cement sheath variations is less than 9%. The research result can provide reference for underground cement sheath monitoring and evaluation method.

Modelling the response of CLLBC(Ce) and TLYC(Ce) SiPM-based radiation detectors in mixed radiation fields with Geant4

CLLBC(Ce) and TLYC(Ce) are novel scintillation materials capable of measuring mixed gamma ray and neutron radiation fields that have gained significant interest in the areas of space and nuclear safety/security science. To date Geant4, the world’s most popular Monte Carlo radiation modelling toolkit, has yet to be effectively used to simulate the full response of these materials when coupled to near ultra-violet Silicon PhotoMultipliers (SiPMs). In this work an experimentally validated Geant4 application has been developed with optimised material composition, optical data tables, and physics transport settings that is able to accurately simulate the response of CLLBC(Ce) and TLYC(Ce) SiPM-based radiation detectors under both gamma ray and neutron irradiation. Experimental benchmarking for five different radioactive sources (Co-60, Cs-137, Eu-152, Am-241, and Cf-252) illustrated that this developed Geant4 application was able to reproduce the position and structure of all major spectral features (full energy gamma ray photo-/neutron capture peaks, X-ray escape photopeaks, Compton edge, Compton backscatter peaks, and Compton plateau) to high level of accuracy.

Thermal insulation performance analysis of high rise building envelope based on finite element analysis

The current analysis method of thermal insulation performance of building envelope neglects the optimization of temperature control parameters, which leads to poor thermal insulation performance, low thermal insulation rate and weak convincing results. Therefore, a finite element analysis method for the thermal insulation performance of high rise building envelope is proposed. Compton backscattering technique is introduced to analyze the influence of the scattering intensity and the ratio of window width on the heat transfer coefficient of the enclosure. Based on the objective function, the thermal performance parameters of retaining wall are calculated and fused. An adaptive iterative optimization method is used to control the thermal performance of the enclosure using the thermal performance parameters of the enclosure. Through the Compton backscatter detection technology, the decision variables of energy consumption of the thermal insulation materials are obtained, and the temperature control parameters of the walls are optimized. The finite element model of enclosure structure is established by using finite element software. The results of finite element model experiments show that the proposed method has ideal heat preservation rate and energy consumption. Compared with the traditional method, the proposed method can keep the preset temperature.

Development and application of a Monte Carlo virtual detector—A novel nuclear pulse signal generator

The generation of real nuclear pulse signals need a detector and a radiation source. In order to replace some expensive detectors or harmful radiation sources, and precisely evaluate a nuclear detection system, a monte Carlo virtual detector (MCVD) which could simulate different types of detectors and radiation sources was designed to generate nuclear pulse signals. The generated nuclear pulse signals were verified in amplitudes and time intervals, and were applied to test the performance of a multi-channel pulse amplitude analyzer. The results showed that the amplitudes were proportional to the corresponding energies, the time intervals between two consecutive pulses obeyed an exponential distribution, and the generated energy spectrum not only included the amplitude information of the full-energy peak, but also included the amplitude information of the Compton plateau and backscatter peak (scattered signals), etc. Thus, the generated nuclear pulse signals have the physical significance of reflecting all kinds of interaction between the ray and the matters in real detector, and can more precisely evaluate nuclear detection systems.

基于精确准直线阵探测器的康普顿背散射成像仿真

基于精确准直线阵探测器的康普顿背散射成像仿真

Measured and Monte Carlo simulated surface dose reduction for superficial X-rays incident on tissue with underlying air or bone.

Measurement of surface dose reduction effects for superficial x-rays incident on tissue with underlying air or bone and comparison with Monte Carlo simulations of such effects. Further to investigate the correlation between surface dose reduction and changes in Compton backscatter spectra with tissue-bone separation. An Advanced Markus chamber with entrance window facing downstream on the surface of a solid water phantom was used to investigate changes in surface dose with an underlying air or bone interface located at various depths below the surface. Chamber readings were obtained for interface depths ranging from 1 to 100 mm using the 50 kV, 100 kV and 150 kV beams of an Xstrahl 150 x-ray unit, with field diameters (ϕ) = 2.5 cm and 5 cm. For each beam quality and field size the dose correction factor, DCF(t), namely the ratio of measured dose (t) to dose (t = 100 mm) was determined. Monte Carlo simulations of DCF(t) for air and bone interfaces in tissue are used to validate corresponding measured data. For a given beam and field size, the difference between simulated spectra with an air or bone interface at t = 3 mm was used to determine the Compton backscatter from bone at the surface. For air, DCF(t < 40 mm) is less than unity and for a given t DCF(t) decreases as beam energy increases from 50 kV to 150 kV. Conversely for bone DCF(t < 40 mm) increases for a given t with increasing beam energy. In particular for t = 1 mm, ϕ = 5 cm, DCF for air(bone) are 0.90(0.92) and 0.86(0.96) for 50 kV and 150 kV, respectively. For the same tube potentials corresponding factors, ϕ = 2.5 cm, for air(bone) are 0.94(0.96) and 0.92(0.99). Calculated DCF(t) based on Monte Carlo simulations are consistent with experimental observations to within 2%. Monte Carlo simulations of x-ray spectra demonstrate the presence of Compton backscatter from underlying bone in tissue. With bone at 3 mm depth calculated backscatter spectra at the tissue surface suggest that surface dose is influenced by the proximity of bone and that this effect depends on beam quality. This work demonstrates the feasibility of using an Advanced Markus chamber with entrance window facing downstream to investigate surface dose reduction with underlying air or bone in tissue. As the field size decreases and beam quality increases surface dose with underlying bone tends to full backscatter values even though tissue thicknesses are below those normally associated with full backscatter. Conversely with underlying bone close to the surface dose will increasingly fall below full backscatter values as the beam energy is reduced and field size is increased.

Compton back scatter imaging for mild steel rebar detection and depth characterization embedded in concrete

A novel non-destructive Compton scattering technique is described to ensure the feasibility, reliability and applicability of detecting the reinforcing steel bar in concrete. The indigenously developed prototype system presented in this paper is capable of detecting the reinforcement of varied diameters embedded in the concrete and as well as up to 60mm depth, with the aid of Caesium-137(137Cs) radioactive source and a high resolution HPGe detector. The technique could also detect the inhomogeneities present in the test specimen by interpreting the material density variation caused due to the count rate. The experimental results are correlated using established techniques such as radiography and rebar locators. The results obtained from its application to locate the rebars are quite promising and also been successfully used for reinforcement mapping. This method can be applied, especially when the intrusion is located underneath the cover of the concrete or considerably at larger depths and where two sided access is restricted.

An ultracold electron source as an injector for a compact SASE-FEL

Ultracold electron sources based on near-threshold photoionization of laser-cooled atomic gases can produce ultrashort electron pulses with a brightness potentially exceeding conventional pulsed electron sources. They are presently being developed for single shot ultrafast electron diffraction, where a bunch charge of 100 fC is sufficient. For application as an injector for x-ray free electron lasers (FEL) a larger bunch charge is generally required. Here we present preliminary calculations of an ultracold electron source operating at bunch charges up to 1 pC. We discuss the relevant bunch degradation processes that occur when the charge is increased. Using general particle tracer tracking simulations we show that bunches can be produced of sufficient quality for driving a 1 Å self amplified spontaneous emission free electron laser (SASE-FEL) at 1.3 GeV electron energy. In addition we speculate on the possibility of using the ultracold source for driving a 15 MeV SASE-FEL in Compton backscatter configuration into the quantum FEL regime.

Single Side Imaging of Corrosion Under Insulation Using Single Photon Gamma Backscattering

In this work, a gamma ray Compton backscatter technique is used for imaging defects and thickness variations in insulated pipes and metal plates containing depressions of various diameters and at various depths from one side of the object. The scattered radiation was measured by a scintillation detector that scans the object using a two-dimensional mechanical scanning system. The gamma spectrum was displayed with a multichannel analyzer (MCA), and the energy window width was selected so that only Compton single scatter counts were measured. Images were constructed using the LabVIEW computer program. Successful images of defects on the outer surface of the object under the insulation were obtained, and the system was found to be able to detect wall thickness changes in large pipes with walls more than 15 mm thick. Low activity sources of 108 Bq (a few mCi) were used, and the dose rate near the surface is four orders of magnitude lower than conventional industrial radiography sources, permitting it to be much safer.

TU‐A‐9A‐03: Development and Verification of a Forward Model That Assists in Iterative Post‐Processing Algorithms Used to Reduce Blur in Compton Backscatter Imaging Systems

Purpose:In Compton Backscatter Imaging (CBI), the source and detector reside on the same side of the patient. We previously demonstrated the applicability of CBI systems for medical purposes using an industrial system. To assist in post‐processing images from a CBI system, a forward model based on radiation absorption and scatter principles has been developed.Methods:The forward model was developed in C++ using raytracing to track particles. The algorithm accepts phantoms of any size and resolution to calculate the fraction of incident photons scattered back to the detector, and can perform these calculations for any detector geometry and source specification. To validate the model, results were compared to MCNP‐X, which is a Monte Carlo based simulation software, for various combinations of source specifications, detector geometries, and phantom compositions.Results:The model verified that the backscatter signal to the detector was based on three interaction probabilities: a) attenuation of photons going into the phantom, b) Compton scatter of photons toward the detector, and c) attenuation of photons coming out of the phantom. The results from the MCNP‐X simulations and the forward model varied from 1 to 5%. This difference was less than 1% for energies higher than 30 keV, but was up to 4% for lower energies. At 50 keV, the difference was less than 1% for multiple detector widths and for both homogeneous and heterogeneous phantoms.Conclusion:As part of the optimization of a medical CBI system, an efficient and accurate forward model was constructed in C++ to estimate the output of CBI system. The model characterized individual components contributing to CBI output and increased computational efficiency over Monte Carlo simulations. It is now used in the development of novel post‐processing algorithms that reduce image blur by reversing undesired contribution from outside the region of interest.

TH-A-141-07: Characterization of X-Ray Source and Detector Geometry for the Compton Backscatter Imaging System for Medical Applications

Purpose: Clinical applicability of Compton backscatter imaging (CBI) systems for medical purposes was previously demonstrated using a CBI system optimized for industrial purposes. In order to optimize CBI for medical imaging, two key CBI system parameters were characterized: 1) x‐ray source and 2) detector geometry. This data can be used to help design systems with optimal spatial resolution, subject contrast, and SNR across clinical imaging applications. Methods: Phantoms of different dimensions and compositions, as well as segmented detectors, were simulated using MCNP‐X, a Monte Carlo transport code. With each set of simulations, a different energy between 20 keV and 1.5 MeV was evaluated. To maximize the potential of MCNP‐X, multiple in‐house C++ and MATLAB algorithms were created to extract and evaluate relevant data from the plethora of MCNP‐X generated information. An analytical model of the system was created to verify the Monte Carlo results. Results: The best subject contrast was observed at lower incident energies, between 30 and 40 keV, and also for smaller detectors. The SNR peaked at higher energies, between 65 and 75 keV, and at detector pixels adjacent to the source. As expected, the penetration power of the beam increased with energy. The spatial resolution of the system became worse (larger PSF) as the size of the detector increased. The absorbed doses to the phantom, per starting particle, increased with the energy, but were either equivalent to or lower than doses observed in transmission imaging at energies of interest. Conclusion: As part of the optimization of a medical CBI system, potential for better images was shown. The ability to design optimal medical CBI systems with x‐ray tubes within diagnostic energy ranges and detectors compatible with diagnostic spatial constraints was demonstrated. CBI can provide single‐sided imaging capability with equivalent or lower absorbed dose.

The Damage Investigation of Wedge-Shaped Electromagnetic Riveting Structure of CFRP/Aluminium Alloy

Abstract In the aircraft industry, electromagnetic riveting is now widely used in the riveting of wedge-shaped aluminium-alloy structure and carbon-fibre-reinforced polymer (CFRP), but damages to the CFRP often happen. To investigate the reason for the damages, methods of C-scan, x ray, Compton backscatter scanning (CBS), metallography, and thermal deply were applied to study the wedge-shaped riveting structures. The study indicates that the composites by the tail of the rivets, which are close to the edge of the structure, are almost comminuted, and those rivets expand uniformly along the shaft and interference fit with the structure, and at the same time curve toward the edge. The composites around the rivets, which are away from the edge of the structure, are slightly damaged, and these rivets deformed not so uniformly, most of them clearance fit with the structure, and in some joints interference fit and clearance fit occur alternatively. The investigation shows that, in the joints close to the edge, the balance of constraints from the aperture to the rivet is broken by the slope around the tail of the rivet, results in a rightward force working on the rivet tail. The integration of this force and the riveting force curves the rivet instantaneously, which comminutes the right-side composites of the rivet tail. For the rivets away from the edge, the deformation becomes more buckled the longer the rivet, which causes the instability of the fit situation and reduces the damage to the composites.

Comment on “Estimation of organ and effective dose due to Compton backscatter security scans” [Med. Phys., 39, 3396 (2012)

Comment on “Estimation of organ and effective dose due to Compton backscatter security scans” [Med. Phys., 39, 3396 (2012)

Response to "Comment on 'Estimation of organ and effective dose due to Compton backscatter security scans'" [Med. Phys., 39, 3396 (2012)

Response to "Comment on 'Estimation of organ and effective dose due to Compton backscatter security scans'" [Med. Phys., 39, 3396 (2012)

TH‐A‐213CD‐10: A Preliminary Evaluation of An Industrial X‐Ray Backscatter System for Medical Applications

Purpose: To evaluate the advantages of Compton backscatter radiography system as a medical imaging tool by comparing images obtained to traditional transmission radiography methods. Methods: Five phantoms were scanned with a scatter x‐ray imaging (SXI) system and state of the art transmission imaging systems. Four phantoms contained biological tissue equivalent samples used to exemplify objects found in medical imaging scenarios. For a complex biological setting a euthanized 60 lb pig was scanned. Parameters such as the x‐ray tube voltage, x‐ray tube current, pixel integration time, stand‐off distance, detector type and detector collimation were varied. Images acquired with the scatter and transmission modalities were compared by observing the differences between the mean pixel value and standard deviation of regions within the images. Visual comparisons between images were also used. Results: The contrast differences between SXI and transmission images varied based on phantom composition and placement of objects within them. As a result, neither system showed better overall object contrast across all phantom scans. SXI images of bone at 1.6 cm depth and 7.8 cm depth revealed a 30.3% change in contrast while transmission images showed a 0.1% difference in contrast. Standard deviation of the mean pixel values (noise) in the SXI images ranged from 13.7% – 21.1% whereas the standard deviation for the transmission images ranged from 3.1% to 6.6%. Detector collimation prevented the detection of surface scatter and better represented objects deeper within a phantom. Conclusions: Clinical applicability of an industrial SXI system for medical applications was demonstrated. Exposures with the SXI system required access from only one side of a patient, giving it a smaller form factor and eliminating the spatial constraints imposed by traditional transmission x‐ray imaging systems. Additionally, depth information was observed in SXI images, potentially reducing the number views necessary to properly diagnose patients.

Estimation of organ and effective dose due to Compton backscatter security scans

To estimate organ and effective radiation doses due to backscatter security scanners using Monte Carlo simulations and a voxelized phantom set. Voxelized phantoms of male and female adults and children were used with the GEANT4 toolkit to simulate a backscatter security scan. The backscatter system was modeled based on specifications available in the literature. The simulations modeled a 50 kVp spectrum with 1.0 mm-aluminum-equivalent filtration and a previously measured exposure of approximately 4.6 μR at 30 cm from the source. Photons and secondary interactions were tracked from the source until they reached zero kinetic energy or exited from the simulation's boundaries. The energy deposited in the phantoms' respective organs was tallied and used to calculate total organ dose and total effective dose for frontal, rear, and full scans with subjects located 30 and 75 cm from the source. For a full screen, all phantoms' total effective doses were below the established 0.25 μSv standard, with an estimated maximum total effective dose of 0.07 μSv for full screen of a male child. The estimated maximum organ dose due to a full screen was 1.03 μGy, deposited in the adipose tissue of the male child phantom when located 30 cm from the source. All organ dose estimates had a coefficient of variation of less than 3% for a frontal scan and less than 11% for a rear scan. Backscatter security scanners deposit dose in organs beyond the skin. The effective dose is below recommended standards set by the Health Physics Society (HPS) and the American National Standards Institute (ANSI) assuming the system provides a maximum exposure of approximately 4.6 μR at 30 cm.

Deducing Electron Properties from Hard X-ray Observations

X-radiation from energetic electrons is the prime diagnostic of flare-accelerated electrons. The observed X-ray flux (and polarization state) is fundamentally a convolution of the cross-section for the hard X-ray emission process(es) in question with the electron distribution function, which is in turn a function of energy, direction, spatial location and time. To address the problems of particle propagation and acceleration one needs to infer as much information as possible on this electron distribution function, through a deconvolution of this fundamental relationship. This review presents recent progress toward this goal using spectroscopic, imaging and polarization measurements, primarily from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Previous conclusions regarding the energy, angular (pitch angle) and spatial distributions of energetic electrons in solar flares are critically reviewed. We discuss the role and the observational evidence of several radiation processes: free-free electron-ion, free-free electron-electron, free-bound electron-ion, photoelectric absorption and Compton backscatter (albedo), using both spectroscopic and imaging techniques. This unprecedented quality of data allows for the first time inference of the angular distributions of the X-ray-emitting electrons and improved model-independent inference of electron energy spectra and emission measures of thermal plasma. Moreover, imaging spectroscopy has revealed hitherto unknown details of solar flare morphology and detailed spectroscopy of coronal, footpoint and extended sources in flaring regions. Additional attempts to measure hard X-ray polarization were not sufficient to put constraints on the degree of anisotropy of electrons, but point to the importance of obtaining good quality polarization data in the future.