Determination of naturalα-radionuclides related to millisecond order lives in environmental samples using the time interval analysis (TIA) method

Simultaneous determination of radionuclides separable into natural decay series by use of time-interval analysis

“…The measuring system consists of an α-LSC (Ordera 8100AB) called Perals, a multi-channel analyzer (MCA, Seiko EG&G, 7800), and a personal computer (Epson PC-486 SE) with a timer/counter module (Contec, TIR-6) having a time resolution of 0.1 ms. Details of the assembly have been presented in elsewhere [3,4,5]. The Perals spectrometer contains a pulse shape discrimination (PSD) circuit to reject pulses caused by β-particles and γ-rays and to extract pure α-pulses.…”

“…9(b), the number of correlated total events is obtained from the initial exponential decay curve over the noise (horizontal line), which is due to random events. The exponential decay component was extracted from the data for the correlated events or for analysis of the radionuclide after correction with the overall yield from the 225 Ra-tracer [1,2,3,4,5,6]. It should be emphasized that the use of a 225 Ra-tracer is helpful in determining the other radium isotopes.…”

“…A delayed coincidence method, time-interval analysis (TIA), was originally developed in our laboratory to determine the thorium decay series in environmental samples by use of liquid scintillation counting with a personal computer [1,2,3,4]. The TIA method is based on measuring correlated α-decay events from daughter nuclides with lifetimes of the order of milliseconds or sub-milliseconds, thereby enabling their discrimination from random decay or background events [2,3].…”

“…Two different types of statistical analysis, single or multiple period time-interval analysis (STA and MTA, respectively) were evaluated using theoretical functions of the time interval distribution curve [2]. From experimental data and simulation tests, an MTA method, which includes all pulse time intervals within a fixed time, was found to be more reliable for selective extraction of decay events with millisecond lifetimes [2,4].…”

“…In addition to 222 Rn→ 216 Po (T 1/2 145 ms) (Th-series) the TIA-MTA method has been applied to the determination of two other correlated α-α decay events, including 219 Rn→ 215 Po (T 1/2 1.78 ms) (Ac-series) and 221 Fr→ 217 At (T 1/2 32.3 ms) (Np-series) [3,4,5,6]. The members of the Np-series are well known to consist of artificial decay series, so 225 Ra in this series could be used as a yield tracer for natural radium isotopes by the TIA method with the growth relationship of transient equilibrium [5].…”