Standardization and half-life of 201Tl by the 4π(x,e)-γ coincidence method with liquid scintillation counting in the 4π-channel

A high-quality solution of 201Tl has been standardized by the 4π(x,e)-γ coincidence method in conjunction with efficiency extrapolation. Liquid scintillation was utilized for the detection of the X-rays and electrons in the 4π-channel. The accuracy of the technique was verified by submitting a standardized sample to the International Reference System (SIR) for comparison with activity results obtained from other methods. The decay of one of the sources was followed over a 2-week period by measuring the activity with this direct method on 91 occasions. The resulting 201Tl half-life was (3.0400 ± 0.0028) days. (Author)