Rod phantom dimensions - Does size matter?

The international standard ISO 4037-3:1999 recommends a cylindrical polymethyl methacrylate rod phantom of 300 mm length and 19 mm diameter for the calibration of extremity dosemeters worn on the finger. No tolerances are stated. This paper investigates the influence of the actual rod phantom dimensions on the calibration results of finger dosemeters. For this purpose, thermoluminescence detectors were attached to rod phantoms of different size and irradiated at the PTB reference X-ray fields. Rod phantoms with a diameter of (19 ± 1) mm and a length of at least 100 mm can be considered to be equivalent for the calibration of finger dosemeters, since the variation in the calibration results is below the significance level of 1%. The decrease in the response towards the edge of the phantom is negligible as long as the distance from the nearest edge exceeds 10 mm. (authors)