Electronic X-Ray Systems For Field Aircraft Inspection
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Downloaded from https://www.cambridge.org/core. Cambridge University Main, on 09 Feb 2020 at 18:24:31, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-503-63
10 line pairs/mm) and ASTM E 1025 plaque-hole type image quality indicators (IQI's) on V4 inch aluminum plate. The test piece was evaluated with a variety of electronic systems including photostimulable storage phosphors, flat panel imagers, scintillator-camera combinations, and reverse geometry x-ray (RGX). The evaluations were based on measurements of resolution, contrast sensitivity, and the ability to detect the defects in the honeycomb structure. RESULTS The Phase I evaluation also considered electronic system cost since that will be a key issue in determining the economic feasibility for converting a film x-ray operation to a nonfilm electronic system. Discussions with Air Force field personnel indicated that annual costs for film and supplies varied widely, from approximately $10,000 to almost $150,000. These figures do not include the indirect waste disposal costs. Cost analysis with a three year pay-back basis would allow the consideration of electronic systems with a price in the range of $30,000 to $450,000 for field inspection applications. Many systems with good technical capability were within this wide price range and are available either now or within a year. Technical evaluations included storage phosphors, scintillator-camera systems, flat panel imagers and the reverse geometry method. Brief descriptions of these techniques follow. The storage phosphor method depends on a photostimulable reaction in phosphors such as europium activated barium fluorohalide [1,2]. Energy trapped in the phosphor material on x-ray exposure is released as light photons when the irradiated phosphor is exposed to red light, typically from a He-Ne laser. As the storage phosphor is scanned by the red laser, the light emitted from each spot is collected by a photomultiplier tube and coordinated with the location of the laser scanning spot to create an image. The light intensity emitted from the x-ray exposed phosphor is linear with x-ray exposure over five orders of magnitude [1-4]. The phosphor sheets Line Pair Gage (1.8 - 3.15 lp/mm)
ASTM IQl's on 1/4" Aluminum
raphite Skin Honeycomb Core
Aluminum Skin, Al Honeycomb Core
Core Unbonds Excess Adhesive
Crushed
Core
Lm 0
Line Pair Gage (2-10 lp/mm)
Figure 1. Diagram of test piece used for initial x-ray system evaluation.
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Downloaded from https://www.cambridge.org/core. Cambridge University Main, on 09 Feb 2020 at 18:24:31, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-503-63
can be handled in a cassette and exposed similar to film, so implementation should be straightforward. The storage phosphor sheets are faster than medium speed x-ray film by factors of 4 to 10 [3]. Major advantages of this digital image approach are that no chemicals are required for
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