Measurement of Ra in water via pulsed ionization chamber (PIC) radon detector.

Ra (t = 3.6 d) has been widely used as a tracer in environmental water research. Here, we present a new method for measuring Ra in natural waters using a pulsed ionization chamber (PIC)-based radon detector. This method is based on the measurement of the Ra daughter isotope Rn (thoron) after reaching secular equilibrium within 7 min. Radium isotopes are concentrated on ''Mn-fibers'' before measurement of Rn, which can be distinguished from Rn by the difference in their half-lives. The measurement efficiency of the method is 0.20 ± 0.01 cps/Bq at an optimum airflow rate of 1.0 L/min and a water/Mn-fiber weight ratio of 1.0. Results from natural water samples obtained by this method agree well with analysis via RaDeCC, an established technique for Ra assessments. Since the PIC system is lighter compared to RaDeCC, easier to operate, and does not require the usage of helium carrier gas and desiccant, this method is recommended for in-situ Ra measurement in long-term fieldwork with limited logistical support.