Transmission density is an important physical property for exposed films in the fields of medicine, non-destructive testing, photography, and graphic arts. Standards for transmission density are provided by the National Institute of Standards and Technology (NIST) in the form of Standard Reference Materials (SRMs). These standards are film step tablets, 254 mm long by 35 mm wide, with steps extending the width of each film and equally spaced along its length. A double emulsion x-ray film is used for SRM 1001 while a single emulsion photographic film is used for SRM 1008. The steps have increasing transmission densities from approximately 0.1 to 4 from one end of the film to the other. SRM 1001 has 17 steps, while SRM 1008 has 23.The transmission densities of film step tablets for both SRM 1001 and 1008 are determined with an instrument using the diffuse influx mode. Diffuse illumination is achieved with a flash opal, while directional detection is accomplished with a lens system. The transmitted radiant flux is detected by a temperature-controlled silicon (Si) photodiode with amplifier electronics capable of measuring signals spanning seven ordersof magnitude. The instrument is designed to automatically measure many films using computerized data acquisition and control.The organization of this Special Publication is as follows. The measurement equations relevant to the determination of transmission density using the diffuse influx mode are derived in section 2. The instrument used for measuring transmission density is described in section 3; its characterization, particularly in relation to the applicable international standards for this measurement, is detailed in section 4; and its operation is discussed in section 5. Finally, the uncertainties in the measured transmission density resulting from various components are derived in section 6.
Citation: Special Publication (NIST SP) - 260-135Report Number:
NIST Pub Series: Special Publication (NIST SP)
Pub Type: NIST Pubs
densitometer, diffuse transmission, standard reference materials, transmission density