Abstract
Method of measurement and result of processing of the \({}^{213}\) Po \(\alpha\) -active isotope half-life data measured in long-run continuous measurement with the underground low-background TAU-3 set-up are described. The set-up consists of two scintillation NaI(Tl) \(150\times 150\) mm \({}^{2}\) detectors and double-layer ( \(h_{\textrm{layer}}=1\) mm) plastic scintillator detector (PCD) with \(d=18\) mm. Source of the \({\dots}{}^{213}\textrm{Bi}\to{}^{213}\textrm{Po}\) … decays was placed between the PSD layers. The half-life was calculated from a decay curve. The curve was constructed from delay values between \(\beta\) - and \(\alpha\) -pulses detected by the PSD. Two methods were used for the event selection. The PSD pulses coincided in 16 mcs time window were selected in the first case (double coincidences). Additional pulse of the NaI detected \(\gamma\) -quantum from the \({}^{213}\) Bi decay was used in the second case for a validation of the \({}^{213}\) Po birth and decay (triple coincidences). The values \(T_{1/2}=3.6970\pm 0.0005\) mcs for the double coincidences and \(T_{1/2}=3.6812\pm 0.0006\) mcs for the triple coincidences were obtained for \({}^{213}\) Po half-life. Possible reasons of the result difference are discussed.
