Search

Correctly modeling the continuous photon spectrum of X-ray tubes requires detailed knowledge of the probability distribution of electron properties at the time of X-ray photon creation, in particular electron energy, depth within the target, and direction of movement. Semi-analytical X-ray spectrum models frequently assume a very simplified or even uniform distribution of electron direction. In the case of thick targets and small deviations from normal incidence this is a useful approximation. For thin targets or large deviations from normal incidence the correct distribution of electron directions becomes more important. As calculation speed is an important aspect of semi-analytical models compared to Monte Carlo simulations, fast evaluation of the distribution of electron properties is highly desirable. The approach presented here numerically evaluates the evolution of a discrete probability distribution of electron properties due to single electron scatter interactions within a plane target. This allows capturing the important aspects of the electron distribution while achieving runtimes of a few seconds up to a minute on a standard office PC. [ABSTRACT FROM AUTHOR]

Within the framework of the European project PICASSO, the radiographic simulator aRTist (analytical Radiographic Testing inspection simulation tool) developed by BAM has been extended for reliability assessment of film and digital radiography. NDT of safety relevant components of aerospace industry requires the proof of probability of detection (POD) of the inspection. Modeling tools can reduce the expense of such extended, time consuming NDT trials, if the result of simulation fits to the experiment. Our analytic simulation tool consists of three modules for the description of the radiation source, the interaction of radiation with test pieces and flaws, and the detection process with special focus on film and digital industrial radiography. It features high processing speed with near-interactive frame rates and a high level of realism. A concept has been developed as well as a software extension for reliability investigations, completed by a user interface for planning automatic simulations with varying parameters and defects. Furthermore, an automatic image analysis procedure is included to evaluate the defect visibility. The radiographic modeling from 3D CAD of aero engine components and quality test samples are compared as a precondition for real trials. This enables the evaluation and optimization of film replacement for application of modern digital equipment for economical NDT and defined POD. [ABSTRACT FROM AUTHOR]

Code Validation is a permanent concern in computer simulation, and has been addressed repeatedly in eddy current and ultrasonic modelling. A good benchmark problem is sufficiently simple to be taken into account by various codes without strong requirements on geometry representation capabilities, focuses on few or even a single aspect of the problem at hand to facilitate interpretation and to avoid that compound errors compensate themselves, yields a quantitative result and is experimentally accessible. In this paper we attempt to address code validation for one aspect of radio-graphic modelling, the scattered radiation prediction. An update of the results of the 2008 benchmark is presented. Additionally we discuss the extension of this benchmark on the lower energy part for 60 and 80 keV as well as for higher energies up to 10 MeV to study the contribution of pair production. Of special interest will be the primary radiation (attenuation law as reference), the total scattered radiation, the relative contribution of scattered radiation separated by order of scatter events (1st, 2nd, ..., 20th), and the spectrum of scattered radiation. We present the results of three Monte Carlo codes (MC-Ray, Sindbad and Moderato) as well as an analytical first order scattering code (VXI) and compare to MCNP as reference. [ABSTRACT FROM AUTHOR]

Code Validation is a permanent concern in computer modelling, and has been addressed repeatedly in eddy current and ultrasonic modeling. A good benchmark problem is sufficiently simple to be taken into account by various codes without strong requirements on geometry representation capabilities, focuses on few or even a single aspect of the problem at hand to facilitate interpretation and to avoid that compound errors compensate themselves, yields a quantitative result and is experimentally accessible. In this paper we attempt to address code validation for one aspect of radiographic modeling, the scattered radiation prediction. Many NDT applications can not neglect scattered radiation, and the scatter calculation thus is important to faithfully simulate the inspection situation. Our benchmark problem covers the wall thickness range of 10 to 50 mm for single wall inspections, with energies ranging from 100 to 500 keV in the first stage, and up to 1 MeV with wall thicknesses up to 70 mm in the extended stage. A simple plate geometry is sufficient for this purpose, and the scatter data is compared on a photon level, without a film model, which allows for comparisons with reference codes like MCNP. We compare results of three Monte Carlo codes (McRay, Sindbad and Moderato) as well as an analytical first order scattering code (VXI), and confront them to results obtained with MCNP. The comparison with an analytical scatter model provides insights into the application domain where this kind of approach can successfully replace Monte-Carlo calculations. [ABSTRACT FROM AUTHOR]

Efficient and reliable nondestructive evaluation techniques are necessary to ensure the safe operation of complex parts and construction in an industrial environment. Radiography is one of the classical nondestructive testing techniques widely applied in industry. Over the years modeling became more and more important in modern NDE. It is increasingly used to optimize techniques for complex applications and to support the preparation of written procedures. Hence, computer modeling has to be able to handle all significant properties of a NDE system with sufficient accuracy. In case of radiographic applications the model includes the radiation source, the interaction of radiation with material, the detection process, and the geometrical description of the part or the construction. As known from practice the last can be very complex and requires a description that allows the handling of arbitrary geometries. The link between NDE models and CAD provides the ability to quantitatively evaluate complex inspection procedures. Depending on the formulated inspection problem or the influencing factors that should be accessed by modeling an appropriate physical model has to be chosen to describe the underlying interaction mechanisms. For high energy applications the description of the radiation source, like the spectrum of a LINAC, becomes essentially difficult. An approach is discussed to overcome this difficulty. The developed simulation capabilities are used to assess the reliability of the radiographic inspection of thick section welds for a special application. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The purpose of the 2014 WFNDEC RT benchmark study was to compare predictions of various models of radiographic techniques, in particular those that predict the contribution of scattered radiation. All calculations were carried out for homogenous materials and a mono-energetic X-ray point source in the energy range between 100 keV and 10 MeV. The calculations were to include the best physics approach available considering electron binding effects. Secondary effects like X-ray fluorescence and bremsstrahlung production were to be taken into account if possible. The problem to be considered had two parts. Part I examined the spectrum and the spatial distribution of radiation behind a single iron plate. Part II considered two equally sized plates, made of iron and aluminum respectively, only evaluating the spatial distribution. Here we present the results of above benchmark study, comparing them to MCNP as the assumed reference model. The possible origins of the observed deviations are discussed. [ABSTRACT FROM AUTHOR]

The purpose of this benchmark study is to compare simulation results predicted by various models of radiographic testing, in particular those that are capable of separately predicting primary and scatter radiation for specimens of arbitrary geometry. [ABSTRACT FROM AUTHOR]

The new standard ISO 17636-2:2013 "NDT of welds: Radiographic testing - Part 2: X- and gamma ray techniques with digital detectors" describes a complex procedure for film replacement by phosphor imaging plates and digital detector arrays. RT modeling software should consider these detector types, X-ray film, and the standard requirements for image quality. Practitioners expect the same visibility of image quality indicators (IQI) in the simulated radiographs as in the experimental exposures. The proposed benchmark test is based on the comparison of experimental radiographs taken at BAM with modeled ones of participants. The experimental setup and the determination of the equivalent penetrameter sensitivity (EPS) as described in the procedure of ASTM E 746 are used for quantitative evaluation of the achievable contrast sensitivity for step hole IQIs as considered in Annex B of ISO 17636-2. System classification data for Computed Radiography (CR) and film systems will be provided by BAM according to ISO 11699-1 for selected film systems and according to ASTM E 2446 for selected CR systems. The classification of films and digital detectors is based on the measurement of the dose response function, the basic spatial resolution (SRb) of the image, and the measured image noise, which depends on the detector efficiency, the quantum statistics, and the detector fixed pattern noise. [ABSTRACT FROM AUTHOR]

Determining scatter ratios at high energies (>∼1 MeV) presents challenges not immediately obvious from measurements at conventional X-ray energies. This includes reduced attenuation even in heavy elements as well as a stronger forward bias of scattering. In order to check the reliability of different measurement setups with regard to material thicknesses, distances, and collimation, attenuation and scattering were separately simulated using a Monte Carlo model. The simulation results help in understanding the sources of radiation scattered into the detection area, thereby aiding in eliminating undesired contributions. [ABSTRACT FROM AUTHOR]

A model is discussed which describes the generation of X-rays in conventional tubes using tabulated Bremsstrahlung energy spectra depending on three variables: the target atomic number, the incident electron kinetic energy, and the fraction of energy radiated. The constructed model includes technical tube parameters like kilovoltage, target material and target angle to also account for self-absorption in the target, as well as radiographic parameters like filtering. Additionally a parameter-free description of the characteristic radiation is included in the model. With the help of the simulation tool the influence of parameters can be separately studied. The validity of the proposed model is shown by measurements. This research is supported by the German Federal Ministry of Economics and Technology under contract MNPQ transfer II D 5-30/06. [ABSTRACT FROM AUTHOR]

A method of efficiently calculating transport of electrons when injected into atomic matter with some initial energy is discussed. In contrast to neutral particles, movement of electrons and other charged particles within atomic matter is governed to a large extent by Coulomb scattering, resulting in a large number of individual interactions. The method based on a novel model of grouped trajectories is developed without using multiple scattering theory. The corresponding numerical algorithm allows achieving high computational speed as well as accuracy. The method can be used to acquire different distributions of electron characteristics, namely energy, direction of movement, position within and point of ejection from the object. Ionization, excitation and radiative energy losses of the electrons are considered via a combined stopping power. [ABSTRACT FROM AUTHOR]

In radiography, irradiating the object and recording the transmitted radiation gives information about the inner structure of an object. The transmitted radiation consists of a primary and a scattered component. The Monte Carlo method allows the detailed description of the physics of radiation transport. On the other hand, it is necessary to handle complex object geometries to be able to simulate realistic inspection scenarios. Standard Monte Carlo programs like the Monte Carlo n-particle transport code MCNP (Los Alamos National Laboratories) use mainly simple geometrical forms such as parallelepipeds, ellipsoids, or planes to construct complex geometries in a proprietary way. Here a model is presented that combines the Monte Carlo method with the world of CAD. Components are described as closed triangulated surfaces using STL as exchange format, which is supported by all CAD systems. The opportunities of the presented Monte Carlo simulation tool are discussed in terms of various examples and compared to MCNP. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

In transmission radiography, information about an object is obtained by irradiating the object and recording the transmitted radiation. The recorded radiation consists of a primary and a scattered component. Conventional models count only for the primary component carrying the information about the object structure. The scattered radiation is considered as a homogeneous background and described as a built-up. But for quantitative radiation technique a detailed knowledge about the contribution of the scattering component is necessary. Monte Carlo transport methods are used to simulate the distribution of scattered radiation produced within engineered components. Because most of these components are complex in geometry a coupling of a CAD-based object description with Monte Carlo transport methods is developed. The paper describes the stochastic simulation scheme and compares the results with standard Monte Carlo codes like MCNP. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]