The current methods for air radon measurement are often of low sensitivity

and the measurement takes longer time.In this paper

based on comparative study and theoretic discussion

we propose an ionization chamber for consecutive air radon measurement.The ionization chamber under ordinary pressure has high detective efficiency in measuring radon and its daughters.A collector unit is equipped for collecting residual radon and its daughters in a measurement.This prevents radon and its daughters from polluting the ionization chamber for a subsequent measurement

a common problem with conventional methods of air radon detection.Feasibility of the design for instantaneous measurement of air radon has been proved in experiments.