Standardisation of ¹³³Ba by efficiency extrapolation method and calibration of ionisation chamber

¹³³Ba has been standardised by direct measurements for the first time in the laboratory using two counting systems: (i) the 4πβ (plastic scintillator) -γ coincidence, (ii) the 4πβ (proportional counter) -γ coincidence. Furthermore, this standardisation experiment demonstrates the performance and applicability of the recently developed 4πβ (plastic scintillator)-γ coincidence system for radionuclides decaying with complex decay schemes as well as for e, X-γ emitters. Additionally, ¹³³Ba solution standards were prepared to calibrate the pressurized 4π γ ionisation chamber and determination of the calibration coefficient. The E_n score is a statistical indicator of the agreement between two independent estimations. Thus, the performance of the PS system was compared to the result obtained with the PC system using the E_n score as specified in the ISO13528:2015. The results of measurements are acceptable if E_n ≦ 1.0. An E_n score of 0.2 was obtained which indicates that, the ¹³³Ba activity concentration obtained by the 4πβ (plastic scintillator) -γ coincidence and 4πβ (proportional counter) -γ coincidence systems are in agreement. This paper presents the standardisation procedure, the results obtained by the measurements and their comparison.