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INTRODUCfIONMeasurement models of NDE techniques have been developed with the purpose of proving the capabilities of NDE techniques for finding flaws. The models take NDE parameters such as ultrasonic frequency, probe diameter, and angle of incidence, and predict the response from the flaw. Models are also a part of quantitative NDE, i.e., the ability to size and characterize flaws and or materials.Nondestructive examination techniques should be utilized throughout the life of a component. This use would incorporate NDE into what is known as unified life cycle engineering. Life cycle engineering considers all aspects of a components life in the design process [1]. The starting point for NDE in the life cycle is the procurement of materials and components. Models are used in the design process to determine the inspectability of the fmished component. Another use for models is the choice of NDE technique and the determination of optimum NDE parameters. Also, in-service inspection needs can be addressed by models [2]. Neutron radiography is one of the types of NDE currently practiced. The remainder of this paper will focus on modeling of this method. Conventional Neutron RadiographyCustomary neutron radiography has four essential components. A source of neutrons is needed. This source is usually either a reactor, an accelerator, or a spontaneous neutron source such as californium-252. Since thermal neutrons are used in radiography, the highly energetic neutrons from fission sources must be slowed. The second requirement for neutron radiography is a means of collimating the neutrons from the nonisotropic source into a parallel beam. The third need of neutron radiography is the sample. An example of a legitimate sample for use with neutron radiography would be a part which is being inspected for corrosion. The low Z material in the corrosion is relatively easy to detect with neutron radiography.A method of detection is the final necessity of neutron radiography. The transfer method utilizing an indium foil is commonly employed. The indium foil is placed behind

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