Direct Measurement of Radioactivity Contents in Radioactive Selfluminous Paint which is Used for watches and Clocks in the State of Painted on the Plate

Abstract

In 1967, A Recomendation of IAEA, concernning Radiation Protection Standard for Radioluminous Timepiece was issued.
Accordingly checking method become necessary for control radioactivity which is used for timep ece. After studied about the method of direct measurement, the following have been concluded.
I. The method of measurement for Pm-147 radioactive selfluminous Paint.
(1) To convert all beta emission to bremsstrahlung, Samples were covered with acryl resin plate, thickness 1mm,
(2) Measurement of bremsstrahlung was made by wide end window GM tube. (3mg/cm², 50mm dia)
(3) To eliminate the geometrical effect, the GM tube was set at 10cm far from the source and measurable area was restricted under 60mm diameter.
(4) The cpm of samples were compared with cpm of standard Pm-147 radioactive selfluminous paint which was measured by the same method. As the results, the inspection of radioactivity used was able to achieve under the error of 10%.
II. The method of measurement for H-3 radioactive selfluminous paint.
(1) Total luminousity of H-3 radioactive paint was measured by photomultiplier tube.
(2) To eliminate the geometrical effect, the height of PM from source was fixed 25mm and the measurable area was restricted under 25mm diameter.
(3) The luminousity of Samples were compared with the standard H-3 radioactive selfluminous paint which was the similar product as samples, and its decay of luminousity was well controled. As the result, the error of this measurement will be about 10%.