Browsing by Subject "Neutron radiography"

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An evaluation of Quantification of Margins and Uncertainties for a neutron radiography application
(2020-08-11) Ung, Annie; Charlton, William S.
Quantification of Margins and Uncertainties (QMU) is a framework that was first introduced to understand the knowns and unknowns of an application. It is used to analyze the reliability of a system by evaluating its confidence ratio. This involves identifying, characterizing, and analyzing any thresholds, margins, and uncertainties that may influence a system’s functionality. To understand the importance of it, the QMU framework is applied to a neutron transport problem, specifically neutron radiography. This thesis showcases extensive work that has been done on neutron radiography at the University of Texas at Austin’s Thermal Neutron Imaging Facility (TNIF). Many parameters of the image quality of the radiographs were measured using an American Society for Testing and Materials (ASTM) standard. This experimental set-up was then simulated using MCNP 6.2, a radiation transport tool that originated from Los Alamos National Laboratory. Aspects pertaining to the radiograph standard were investigated further for the application of the QMU framework by evaluating both the experimental and simulation results. From this analysis, the lowest confidence ratio was found to be 11.3 and the highest was 376.2. These values are greater than 1 therefore this system is recognized as reliable. Areas with lower confidence ratios are more likely to experience failure so these regions should be avoided when imaging if at all possible.
Development of a neutron radiography and computed tomography system at a university research reactor
(2006-05) Haas, Derek Anderson, 1981-; Biegalski, Steven R.
Neutron radiography is a non-destructive analysis tool that complements X-ray transmission radiography. The use of neutrons provides the ability to image the interior of an object that has a metal core of steel or lead that would shield the interior from X-ray inspection. Neutron tomography is the use of a set of images of a single sample taken at various angles to produce a three dimensional rendition of the sample that greatly increases the effectiveness of neutron radiography as a non-destructive testing tool. A neutron radiography and tomography system has been built at the 1.1 MW TRIGA Mark II nuclear research reactor at The University of Texas at Austin in the Nuclear Engineering Teaching Lab. The Texas Neutron Imaging Facility is located on beam port five of the reactor and is housed in a shielding cave made of concrete to minimize radiation dose to users. The system itself integrates a sample positioning system and neutron sensitive camera through the use of a control code written in National Instruments Labview software. The code was written to increase the efficiency of the imaging process and to provide flexibility in the system. Precise sample positioning and timing of image acquisition provided by the code allows for the collection of data that can be used in computed tomography. The system has produced results in the form of radiographs and 3-D reconstructions of sample objects.
Evaluation of the impact of non-uniform neutron radiation fields on the dose received by glove box radiation workers
(2004) Crawford, Arthur Bryan; Biegalski, Steven R.
The effort to estimate the radiation dose received by an occupationally exposed worker is a complex task. Regulatory guidance assumes that the stochastic risks from uniform and non-uniform whole-body irradiations are equal. An ideal uniform irradiation of the whole body would require a broad parallel radiation field of relatively high-energy radiation, which many occupationally exposed workers do not experience. In reality, workers are exposed to a non-uniform irradiation of the whole body such as a radiation field with one or more types of radiation, each with varying energies and/or fluence rates, incident on the worker. Most occupational radiation exposure at LANL is due to neutron radiation. Many of these exposures originate from activities performed in glove boxes with nuclear materials. A standard Los Alamos 2x2x2 glove box is modeled with the source material being clean weapons grade plutonium. Dosimeter tally planes were modeled to stimulate the various positions that a dosimeter can be worn. An anthropomorphic phantom was used to determine whole body dose. Various geometries of source position and phantom location were used to determine the effects of streaming on the radiation dose a worker may receive. Based on computational and experimental results, the effects of a non-uniform radiation field have on radiation dose received by a worker in a glove box environment are: 1) Dosimeter worn at chest level can overestimate the whole body dose between a factor of two to six depending on location of the phantom with the source material close to the front of the glove box, 2) Dosimeter should be worn at waist level instead of chest level to more accurately reflect the whole body dose received, 3) Dose can be significantly higher for specific locations of the worker relative to the position of the source, 4) On the average the testes contribute almost 44% of the whole body dose for a male, and 5) Appropriate design considerations such as more shielding on the bottom of the glove box and controls such as the use of internal or external shielding can reduce the effects on dose from these non-uniform fields.
Measuring fluid phase change in capillary tubes using neutron radiography
(2010-05) Gilbert, Andrew James; Deinert, Mark; Hidrovo, Carlos
Neutron radiography is well suited to non-invasive imaging of water within metal containers. The goal of this work is to determine if neutron radiography can be used to image water freezing within a 1.6mm diameter capillary tube with the ultimate goal of observing this phenomena within fuel cells. In this work, radiography was completed at the Thermal Neutron Imaging Facility in the Nuclear Engineering Teaching Lab at The University of Texas at Austin. The source of neutrons was a TRIGA Mark II nuclear research reactor capable of 1.1 MW steady state power, which creates a neutron flux at the neutron imaging plane in beam port 5 of 5×10^6 neutrons/cm^2s. A scintillation screen and CCD camera are utilized to obtain digital radiographs, in which differences in pixel intensity are related to differences in neutron attenuation. An image processing algorithm was developed in Matlab to extract necessary data from each image, analyze water column images, and compare one to another. Also, a neutron flux model was implemented in Matlab in order to understand how a non-unidirectional neutron flux will affect final results. Raw image intensities of the water column in liquid and solid form were found to differ from expectations by at most 12.0% and 13.3%, respectively from the predictions of the Matlab flux model. A difference in pixel intensity comparing liquid water to solid water data is apparent and quantified. A ratio of pixel intensity for the ice image to the water image at full thickness of the water column is expected to be 1.038. Experimental results find a maximum ratio of 1.027, 1.1% off from expectations.
Scattering correction and image restoration in neutron radiography and computed tomography
(2000-08) Abdelrahman, Magdy Shehata; Abdurrahman, Naeem M.
Neutron radiography and computed tomography are nondestructive imaging techniques for the assessment of internal structure of objects. Neutron scattering in such objects can cause image degradation and complicate image interpretation. The removal of the scattering effect is one of the most challenging problems in neutron imaging. In this work, a new method for scattering correction is being developed. Experimental measurements and Monte Carlo simulations were used to investigate the effect of thermal and fast neutron scattering on neutron image degradation both qualitatively and quantitatively. Neutron scattering degrades the quality of radiographs and in cases of severe scattering, could blur sharp edges in neutron images. In addition, neutron scattering imposes an error in neutron radiography quantitative measurements. In this study, scattering correction was approached in two different ways. The first consisted of image restoration using the Slow Evolution from the Continuation Boundary (SECB) method. The SECB method was investigated and implemented to deblur neutron images for such cases when neutron scattering effect is severe enough to blur produced radiographs. The SECB method is a noniterative linear image deblurring method based on the slow evolution constraint, which is highly effective in suppressing noise amplification. The second approach for a scattering correction, which has been developed for the first time as part of this study, is based on the conjecture that there exists a correlation between the pattern of scattered neutrons as observed from a given side of the object as the object is irradiated from different sides. This suggests rotating the sample with some angle to clear the direct neutron view and obtain an image of pure scattering. The correlation between this side image and the scattering component of the forward image could be used to obtain an estimate of the forward scattering component. The estimated scattering component would then be subtracted from the degraded image to get a scattering-free image. Data manipulation of the scattering side-images was used to correlate the scattering side-image to the forward scattering component utilizing the scattering information outside of the neutron beam scope. Another approach was to implement artificial neural networks to capture the correlations between scattering side-images and the forward scattering components as obtained from numerical simulations for typical samples and utilize these networks to get an estimate of the forward scattering component for the object of interest.