A primary standard for the measurement of alpha and beta particle surface emission rate at the National Metrology Institute of South Africa

An absolute alpha and beta particle measurement system for the calibration of extended area sources has been established at the National Metrology Institute of South Africa (NMISA). Various characteristics of the measurement system were studied. Dead time and optimal values for high-voltage and low-energy discrimination were determined. The surface emission rates from four extended area sources (Am-241, Sr-90/Y-90, Cl-36 and C-14) that were previously certified by National Physical Laboratory (NPL) were measured. The results obtained with the NMISA measurement system and those from the NPL were in excellent agreement with E_n values of below 0.25 being observed for all four sources.