ASTM E2903-13

5.1 One of the factors affecting the image quality of a radiographic image is geometric unsharpness. The degree of geometric unsharpness is dependent upon the focal spot size of the radiation source, the distance between the source and the object to be radiographed, the distance between the object to be radiographed and the image plane (film, imaging plate, Digital Detector Array (DDA), or radioscopic detector). This test method allows the user to determine the effective focal spot size (dimensions) of the X-ray source. This result can then be used to establish source to object and object to image detector distances appropriate for maintaining the desired degree of geometric unsharpness or maximum magnification possible, or both, for a given radiographic imaging application. The accuracy of this method is dependent upon the spatial resolution of the imaging system, magnification, and signal-to-noise of the resultant images.

1.1 The image quality and the resolution of X-ray images highly depend on the characteristics of the focal spot. The imaging qualities of the focal spot are based on its two dimensional intensity distribution as seen from the imaging place.

1.2 This test method provides instructions for determining the effecting size (dimensions) of mini and micro focal spots of industrial X-ray tubes. It is based on the European standard, EN 12543–5, Non-destructive testing - Characteristics of focal spots in industrial X-ray systems for use in non-destructive testing - Part 5: Measurement of the effective focal spot size of mini and micro focus X-ray tubes.

1.3 This standard specifies a method for the measurement of effective focal spot dimensions from 5 up to 300 μm of X-ray systems up to and including 225 kV tube voltage, by means of radiographs of edges. Larger focal spots should be measured using Test Method E1165 Standard Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhole Imaging.

1.4 The same procedure can be used at higher kilovoltages by agreement, but the accuracy of the measurement may be poorer.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.