New rapid method to determine radon and thoron from a single counting sequence using a field portable alpha particle scintillometer

Measurement of soil-gas radon (Rn) concentration is an important parameter in estimating soil Rn potential for a building site. Typically, field methods for grab samples (as contrasted with continuous flow systems) using a protable alpha-scintillometer only considered²²²Rn (T _1/2= 3.8 d) and ignored²²⁰Rn (T _1/2=55 s). Now the calculation permits the determination of the concentrations of both isotopes with a single series of readings. A sample is collected and within 1 minute is introduced into the counting system. A series of 1 minute counts begins immediately and continues for 10 minutes. If high²²⁰Rn concentrations are present, there will be a rapid decay followed by a steady ingrowth of²²²Rn progeny. If very little²²⁰Rn is present, the ingrowth will be seen immediately. In either case, a non-linear least square fitting program from Statgraphics is used to obtain both concentrations at time zero. When inexact timings ranging from 1 to 30 seconds were imposed on the measured data, the method proved to be very robust; the biases did not exceed 15 percent.