Activity measurement of 204Tl by direct liquid scintillation methods

The activity of 204Tl, which is essentially a pure beta-emitter with a 2.6% pure electron-capture branch, has been determined by two direct liquid scintillation methods. These were the triple-to-double coincidence ratio (TDCR) efficiency calculation technique and 4π(X, e)—Xκ coincidence counting. The extracted solution activity concentration given by each method agreed to better than 1% and was also consistent with that given by the CIEMAT/NIST liquid-scintillation efficiency tracing method utilising a 3H standard.