Comparative Investigation and Improvement of Film Radiography Speed for Non-Destructive Inspection of Industrial Specimens

Abstract

Film radiography is still used extensively in industry even though the image recording efficiency of the film is lower than <1% and is much lower at high energy range. The imaging plate is >10 times more sensitive than the conventional screen-film technique but its image reader and the imaging plate are relatively costly. Fading of the image data on the IP is also a problem. This research first emphasizes on improvement of the screen/film speed to reduce the exposure time by using the new PI-200 gadolinium oxysulfide (GOS) fluorescent screen. By using the PI-200 screens, the intensifying factors were found to be approximately 33.6, 39.0 and 61.3 for 100, 130 and 160 kVp x-rays while the IF’s of the conventional lead screens were approximately 2.8, 3.4 and 4.0 respectively. The intensifying factors (IF) for 192Ir and 60Co gamma-rays were found to be approximately 13.7 and 7.3 respectively while the IF’s of the conventional lead screens were approximately 5.8 and 1.4 respectively. The PI-200 screen thus could increase the speed of the conventional lead screen-film by at least 2 times depending on photon energy. Moreover, the sensitivity of the radiographs obtained from the PI-200 was comparable to those obtained from the conventional lead screen film technique. It was also found that the image quality could significantly improve by using lead filter to absorb the scattered gamma-rays at low energy range particularly when the specimens contained light elements such as concrete. In addition, objective of this research was to develop a device to determine the exposure time without need of information on the test specimen such as kind of material and thickness, source activity and source-to-film distance. The device was based on measurement of the transmitted x-ray or gamma-ray intensity by using a small PIN photodiode detector. The detector was mounted with a pulse processing unit and a microcontroller board and connected to a Bluetooth module. The counting data could simultaneously send to a smartphone to display the intensity. Application software was developed to control the measurement as well as to display the counting data. Prior to film exposure, the device was placed behind the specimen at required position to measure transmitted intensity which was inversely proportional to the exposure. Unlike in using the conventional exposure curve, correction factors for source decay, source-to-film distance, specimen thickness and kind of material were not needed. The developed technique and device was finally tested in radiography of the three specimens having different thicknesses to obtain a film density of 2.0 on the required areas. The obtained film densities on the required areas were found to be 1.92, 1.98 and 2.05 which were very satisfactory. The developed technique and device could the make radiographic process economic, convenient and more reliable.