HIGH ENERGY X-RAY AND NEUTRON MODELING AND DIGITAL IMAGING FOR NONDESTRUCTIVE TESTING APPLICATIONS Page: 4 of 14
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HIGH ENERGY X-RAY AND NEUTRON MODELING AND DIGITAL
IMAGING FOR NONDESTRUCTIVE TESTING APPLICATIONS
Anthony W. Davis, Charles R. Hills, Matthew J. Sheats, Thomas N. Claytor
ESA-MT, Los Alamos National Laboratory, MS C914, Los Alamos, NM 87545
Adapting amorphous silicon imagers to the rigors of nondestructive evaluation has required the creation of new tools and
techniques for successful detection of flaws in dense objects. At Los Alamos National Laboratory, extensive use of digital
imagers and a desire to replace film with digital systems has led to additional research into modeling and simulation with an
ultimate goal of improved techniques for using these imagers. The imagers have been used with varying success at x-ray
energies ranging from 70 keV to 20 MeV, as well as with a variety of neutron energies at the Los Alamos Neutron Science
Center (LANSCE). To simulate these diverse situations, a new version of the Monte Carlo Neutron/Photon (MCNP)
simulation package, developed at Los Alamos, is employed (MCNP-X). The rapid simulation of various setups allows the
rapid development of techniques without extensive and costly experimentation or test blocks. The simulations cover digital
radiography as well as computed tomography. The results of these simulations leads to several techniques for digital
radiography and computed tomography unique to amorphous silicon imagers, and provides additional information concerning
the transition from film to digital imaging. Specifically, techniques have been developed to use the order of magnitude speed
advantage of amorphous silicon detectors to provide density resolution in ways not possible with film. Also, the viability of
amorphous silicon detectors at extremely high energies (1-20 MeV) is simulated and tested experimentally.
Keywords: Monte Carlo Simulation, MCNP, amorphous silicon, high-energy radiography, radiography, simulated
radiography, neutron radiography, computed tomography simulation.
Radiography has long been established as a reliable and robust method of nondestructively evaluating many parts of
industrial interest. Welds, material properties, and conformance to design can be readily examined through this established
process. The procedure for radiography has remained essentially unchanged for decades: an x-ray source illuminates the
object of interest and the attenuated beam is measured using photographic film. Once the film is developed, the image is
analyzed and measurements are made using a lightbox or microscope. Electronic detectors have been available for many
years, but their low resolution and high noise limited their use to a very few applications. They were not well suited to the
rigorous specifications of industrial nondestructive analysis. In the past few years, a new generation of detectors have
emerged yielding performance comparable to film, and finally it has become reasonable to propose their use as a replacement
to film detection.
The transition to digital detectors requires a thorough investigation of the technical performance of the detectors compared
with film as well as proposing correct use of digital detectors. Many questions arise as soon as a different detection system is
proposed. There are obvious questions of spatial and contrast resolution and noise, but other non-obvious issues remain
regarding physical installation, energy issues, image interpretation, archiving, training, and analysis repeatability. In short,
replacing film with digital detectors does not involve simply removing film cassettes and replacing them with digital panels.
There are still some applications for which digital detectors cannot replace film, and it is important to identify exactly the
parameters for which digital detectors are superior or inferior to film. Ultimately, for most applications, a digital detector
based radiography system is functionally equivalent to a film system.
The digital detection system that currently performs most acceptably as a replacement for film is based on large format
amorphous silicon detector plates. These detectors are available from a variety of vendors, but their performance and
specifications are very similar. The nominal amorphous silicon detector is 10 by 16 inches in area with around 130 micron
pixel to pixel spacing. These detectors have the best resolution available in a package that will endure the high radiation of
industrial radiography and provide immediate (less than one minute) images.
* Email: firstname.lastname@example.org
OCT 2 C 200
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DAVIS, A. W.; HILLS, C. R.; SHEATS, M. J. & CLAYTOR, T. N. HIGH ENERGY X-RAY AND NEUTRON MODELING AND DIGITAL IMAGING FOR NONDESTRUCTIVE TESTING APPLICATIONS, article, June 1, 2000; New Mexico. (digital.library.unt.edu/ark:/67531/metadc719811/m1/4/: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.