Measurement of the activity of 11C and 22Na sources using a 4π–β–γ coincidence system

Many radiation applications, including positron emission tomography (PET) studies and activation dosimetry, require the knowledge of the activity of short-lived radionuclide samples, whereas relative measurements may be hampered by the absence of a reference source. Using 11C radionuclide as an example, an analytical model based on a probabilistic approach has been set up to predict the activity of a pure positron emitter measured using the 4π–β–γ coincidence technique. The model has been extended to describe the measurement on a 22Na source used to test the measurement technique. Comparison of the modeled results with the measurements confirms the general validity of the model. The model has also been studied for the effect of the variation of key measurement conditions, such as nominal source activity, detector efficiency, detector background levels, and coincidence resolving time. The 4π–β–γ coincidence technique and the results of modeling allow the activity measurements on 22Na and 11C sources with an estimated relative standard uncertainly on the order of one percent.