Chapter 7: Non-destructive Testing Reference procedure Measurement of the Optical Density of X-ray Films Keywords optical density, X-ray film with graded optical densities, film step tablet Quantities and items tested optical density, film step tablet, radiographs Testing range Uncertainty of results 0,2 up to 4,8 from 0,01 to 0,05 Fields of application Verification and calibration of densitometers for measurement of the optical density on radiographs (X-ray films) in industrial radiographic testing Methodology and instrumentation Traceable measurement of optical densities of X-ray films with a calibrated densitometer according to ISO 5-2 (diffuse optical transmission density) Qualification and quality assurance Traceability to a reference standard of the National Institute of Standards and Technology (NIST) and a calibrated step tablet by the Physikalisch -Technische Bundesanstalt (PTB) The densitometer is checked and calibrated periodically by the above mentioned reference standards. Contact: Dr. Uwe Zscherpel Phone: +49 30 8104 3677 E-mail: [email protected] Fax: +49 30 8104 1837 Division 8.3: Radiological Methods Date: Feb. 2014 back to Catalogue of Reference Procedures 1(2) 704en.pdf Reference procedure Chapter 7: Non-destructive Testing Further information Flaws in technical installations or devices can be detected by differences in optical density of X-ray films/ radiographs. It is therefore important for quality assurance of film evaluation, that the optical density is defined and traceable to standards. The optical density is measured by transmission of light through the film according to ISO 5-2 and ISO 5-3. The optical density is defined by: D  lg L0 LF D = diffuse optical density Lo = Luminance in cd/m2 (on the side of the light source before the film, diffuse) LF = Luminance in cd/m2 (on the side of the observer, behind the film, specular) The optical densities measured with a densitometer are traced back onto a NIST-standard respectively a density step tablet calibrated by the PTB. The density step tablets measured with the reference method “Measurement of the optical density” are used in industrial radiography to check the densitometers and therefore for the quality assurance of the exposed x-ray films, i.e. for a proof of the achieved density. The measured density step tablets have to be recalibrated in certain intervals depending on national directives (remeasurement of the optical density). The measurement results are summarized in a certificate. Example for a measured density step tablet with certificate: Date: Feb. 2014 2(2) 704en.pdf