LAUSR

Radon‐in‐air monitor (RAD7, Durridge Co.) has been widely used to measure 222Rn in water samples. RAD7 measures 222Rn via 218Po+ (t1/2 = 3.1 min), which is electrically attracted to a silicon alpha detector. In this study, a new method was developed for measuring 222Rn in water samples by modifying a commercially available pulsed ionization chamber (PIC, FT‐Lab Co.). The PIC detects and amplifies the electric pulses generated by microspace charges produced by 222Rn decay. Two passive PICs (volume: 2 × 400 mL) were combined and modified to form an active system (named Rn‐SNU) that continuously circulates air (~ 1 L min−1). Rn‐SNU is approximately seven to nine times more efficient than RAD7 and does not necessitate a delay of ~ 15 min to reach radioactive equilibrium between 222Rn and 218Po+. However, RAD7 is more accurate in discriminating 222Rn daughters, 218Po+ and 214Po+. In this study, 222Rn was successfully measured in coastal seawater samples using Rn‐SNU connected to a grab bottle. Our results suggest that 222Rn measurements in water samples can be conducted more efficiently and rapidly with an Rn‐SNU than with other widely used instruments and methods.