Use of sum-peak and coincidence counting methods for activity standardization of 22Na

A solution containing the positron emitter 22Na has been absolutely standardized using the 4πβ–γ coincidence counting method and the sum-peak spectrometry counting method. In the 4πβ–γ coincidence method two ways for the activity concentration measurements were used: gating on the 1275 keV photopeak and on the 1786 keV sum-peak where the knowledge of the β+-branching ratio is required. In the sum-peak method the measurements were carried out using three experimental arrangements: the first composed by a well type 5 in.×5 in. NaI(Tl) scintillation crystal, the second by a 3 in.×3 in. NaI(Tl) scintillation crystal placed on the top of the first, resulting in a 4π counting geometry and the third arrangement is a high purity coaxial germanium detector. The results that are obtained by these two methods are compatible within the standard uncertainty values with a coverage factor of k=2 (∼95% of the confidence level). This means that the sum-peak counting with its more simple experimental setup than the complex coincidence 4πβ–γ counting system gives consistent results for the activity standardization of 22Na with smaller uncertainties. Besides, the time period involved to attain the result of the standardization was quite shorter than the coincidence measurements used in this work.