Pulse time interval analysis (TIA) combined with liquid scintillation counting for the determination of environmental α-nuclides: Preparation and utilization of225Ra as a yield tracer

Abstract

Time interval analysis (T1A), which has been verified to be suitable for the selective extraction of correlated successive c~-decay events within a liquid scintillator, was further developed by combining pulse shape discrimination technique and simple chemical analysis. A [3-emitter nuclide, 225Ra, which is suitable for the use as a yield tracer belonging to Np-decay series, was also found to be detectable by the TIA-method after a certain standing period when the radium-extractant (RADAEX) was added small amounts of HDEHP [di (2-ethylhexyl) phosphoric acid], which was proved to keep the equilibrium state between Ra and its descendants. The present counting system (TIA analysis incorporated r has been verified to be applicable to the simultaneous determination of three (including Th, Ac, and Np) decay series, if the chemical purification of radium fraction was applied to the environmental samples using an extractive scintillator in addition to utilization of an a-peak itself at lowest energy for the determination of 226Ra in uranium decay series. This radioanalytical method was practically applied to the determination of natural radionuclides belonging to three decay series in environmental samples and compared to the alpha-spectrometric results using a Si-surface barrier detector (SSB).

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

“…A 1.0 mL aliquot of the scintillator solution, now containing all radium isotopes, was transferred to a standard glass test tube (ϕ=1.0 mm, l=75 mm), and di-(2-ethylhexyl) phosphoric acid (HDEHP) was added to stabilize the solution until the second TIA measurement of the Np-series nuclides, to be made after 20 days. The scintillator solution was purged for 5 min with dry nitrogen gas to expel dissolved 222 Rn and oxygen, which leads to oxygen-quenching in liquid scintillation counting (LSC) [6].…”

“…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.…”

“…Fig. 6) to evaluate the overall yield [6]. Three different synthetic samples with different ratios of 225 Ra to 224 Ra and 225 Ra to 226 Ra have led to acceptable results, complementing the 225 Ra-tracer method and making it more universally useful.…”

“…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].…”