Simultaneous determination of environmental α-radionuclides using liquid scintillation counting combined with time interval analysis (TIA) and pulse shape discrimination (PSD)

Abstract

Some improvements of the detection sensitivity in pulse time interval analysis (TIA) based on selective extraction of successively α-α correlated decay events within millisecond order from random or background events, were established by the utilization of PSD, to reject β/γ-pulses from α-ones and a simple chemical procedure of radium separation, together with the use of well resolved scintillator. By applying the PSD, the contribution of β-decay events was completely eliminated in both the α-spectra and the TIA distribution curves as well as the improvement into clear energy resolution and the enhancement of detection sensitivity for the TIA. As a result, the TIA and α-spectrometric analysis of²²⁶Ra-extract showed the existence of²²³Ra (Ac-series) and β/α-correlated events with correlated life (due to 0.16 ms due to²¹⁴Bi(β)→²¹⁴Po(α)→) along with a singly well resolved α-peak to be useful for the determination of²²⁶Ra (U-series). The difference of half-lives (145 and 1.78 ms) due to²¹⁶Po and²¹⁵Po (direct daughters of²²⁴Ra for Th-series and²²³Ra for Ac-series, respectively) was also proven for the possibility of the simultaneous determination of both correlated events by using the TIA/PSD combined with chemical separation and liquid scintillation counting method. Finally, the simultaneous determination of three natural decay series, which include U-, Th- and Ac-series nuclides, have been conveniently carried out for some environmental samples using the present method combined with²²⁵Ra yield tracer (Np-series).