Effect of gamma window setting on activity measurement of 134Cs by 4πβ(LS)-γ coincidence method

The complex decay scheme of Cs-134 allows the activity measurement of the nuclide by the 4 pi beta(LS)-gamma coincidence method to be performed at different gamma-window settings. This paper describes the activity measurement of Cs-134 by 4 pi beta (LS)-gamma coincidence method based on five gamma-window settings. The use of different gamma-window settings affects the efficiency curve used to determine the activity value. The possible sources that are affecting the efficiency function are discussed. Despite the different efficiency functions obtained from the five gamma-windows, a linear extrapolation can be performed by limiting the fitting range within the highest efficiency range. The results show that the specific activity value of each setting is differed by less than 0.3%, with the mean activity value of (1145.6 +/- 4.4) kBq/g at the reference time. The quoted uncertainty is evaluated at k = 1.