Absolute radioactivity measurement of 60Co, 134Cs and 166mHo by 4πβ−γ anti-coincidence method

A 4πβ−γ anti-coincidence system has been developed for absolute radioactivity measurements with a HPGe γ-spectrometer used as the γ-ray detector and a 4πβ proportional counter as the β detector. The activity of 60Co, 134Cs and 166mHo have been measured with the combined standard uncertainties of 0.24%, 0.33% and 0.44%, respectively. Compared with the results of the National Institute of Metrology and 4πβ−γ coincidence counting system of the China Institute of Atomic Energy, the agreement of the results of 60Co and 134Cs is satisfactory. For 166mHo, the results obtained using other methods by most national and international labs lack sufficient accuracy due to the complex decay scheme of this radio-nuclide. It is also concluded that the result of anti-coincidence measurement is independent of β efficiency.