Absolute activity of (133)Ba by liquid scintillation coincidence counting using the 4pi(e,X)-gamma extrapolation technique.

The Technical Committee for Ionizing Radiation (TCRI) of the Asia Pacific Metrology Programme (APMP) recently organized a regional key comparison of activity measurements of the radionuclide ¹³³Ba. This paper reports on absolute measurements made at the National Metrology Institute of South Africa (NMISA) by the coincidence extrapolation technique, with liquid scintillation counting (LSC) comprising the 4π channel. A detection efficiency analysis was undertaken to predict the maximum efficiency likely to be achieved and to confirm that the method does indeed provide the source disintegration rate for ¹³³Ba. Various experimental and data analysis difficulties to be aware of are discussed in the paper.