100 ev They 10 hey 100 kV Grenz raye 1Mey X-tays 10 Mev rays 100 MeV. Figure: 2 - Wavelengths of Electromagnetic radiation 10km 10º radiowaves hectrays infra-rod rays Xeray eneroy visible light UM. The figure 2 below shows their location in the electromagnetic spectrum. It would be possible to illustrate the other similarities between x-rays and light but, for the most part, the effects produced are so different-particularly their penetration-that it is preferable to consider x-rays and gamma rays separately from other radiations. Hence, it is impractical to focus x-rays and Gamma rays. X-rays and Gamma rays are also refracted, but to such a very slight degree that the most refined experiments are required to detect this phenomenon. For example, light is refracted by glass and, consequently, is capable of being focused by a lens in such instruments as cameras, microscopes, telescopes, and spectacles. X-rays and Gamma rays exhibit all the properties of light, but in such a different degree as to modify greatly their practical behavior. This characteristic is responsible for the ability of x-rays and Gamma rays to penetrate materials that absorb or reflect ordinary light. Their distinguishing feature is their extremely short wavelength-only about 1/10,000 that of light, or even less. NATURE OF X-RAYS AND GAMMA RAYS X-rays and Gamma rays are a form of electromagnetic radiation (EMR), as is light. Certain insulating materials can hold a surface electrostatic charge, which is partially discharged on exposure to X-rays, and can be subsequently made visible - Ionography, Xeroradiography. Various radiation detectors can be used - counters, crystals, photodiodes, semiconductors, either singly or as an array - and a series of point-by-point measurements used to build up an image. Usually today, the fluorescent screen would be viewed either with a closed circuit television camera, or would form part of an X-ray image intensifier. This is fluoroscopy, also called real-time radiography. If the X-rays fall on to a fluorescent screen, the X-ray energy is converted to visible light and the image of a specimen can be seen directly on the screen. Instead of recording the variations of transmitted X-ray intensity on a film, other methods may be used: 1. A film Intensifying screens Please note that the object must be placed between the Source and the Film. Figure: 1 - Basic set-up for conventional film radiography snurce Speciren a D. The developing, fixing, and washing of the exposed film may be done either manually or in automated processing equipment. Itis then washed to remove the fixer and dried so that it may be handled, interpreted, and filed. The film is next put into a fixing bath, which dissolves the undarkened portions of the sensitive salt. After development, the film is rinsed, preferably in a special bath, to stop development. The areas so exposed become dark when the film is immersed in a developing solution, the degree of darkening depending on the amount of exposure. When film is exposed to x-rays, gamma rays, or light, an invisible change called a latent image is produced in the film emulsion. MAKING A RADIOGRAPH A radiograph is a photographic record produced by the passage of x-rays or gamma rays through an object onto a film. Radiographic test and quality assurance personnel must be continually aware of the radiation hazard and cognizant of safety regulations. Radiation can cause damage to or destruction of the cells of living tissue, so it is essential that personnel are adeguately protected. Radiographic NDT processes require the use of X-ray and gamma-ray sources generating great amounts of radiation. SAFETY CONSIDERATIONS Because radiation cannot be detected by any of the five senses, strict compliance with safety regulations is required. CONTENTS S.No Description Page No 1 Introduction 34 2 Making a Radiograph 5 3 Nature of Gamma Rays and X-Rays 6-19 4 Principle of Radiographic Technique ( Filters, screens, Film) 20-34 5 Effect of Developing condition 35-39 6 Geometric Principles 40-46 7 Unsatisfactory Radiographs 47-50 8 Sensitivity 51-57 9 Special Processing Techniques and Film Processing 57-94 10 | Radiographic techniques 94-104 11 Interpretation of Radiographs 105-124 12 Radiation Safety 124-133 Radiographic Testing WMM. Baixe Apostila de radiografia PCN e outras Manuais, Projetos, Pesquisas em PDF para Engenharia Física, somente na Docsity! THE BRITISH INSTITUTE OF NON-DESTRUCTIVE TESTING Es DA ia a PCN RADIOGRAPHIC FILM INTERPRETATION (RTFI) MATERIAL WMM.
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