UNCERTAINTY OF MEASUREMENT IN THE RESPONSE TEST OF A THYROID MONITOR.

A test device consisting of an I-131 source, a phantom on a 3D moving table, and a NaI(Tl) scintillation detector on a fixed flat table was developed to carry out response tests of a thyroid monitor. A measurement uncertainty due to variation of configuration of the source and the detector, as well as other factors, was estimated. The estimated relative standard uncertainty of measurement at a source-detector distance of 100 mm, which was deduced to be the optimum, was 1.9%. This is sufficiently small for calibrating a thyroid monitor used for radiation protection.