NEW RAPID METHOD TO DETERMINE RADON AND THORON FROM A SINGLE COUNTINGSEQUENCE USING A FIELD PORTABLE ALPHA-PARTICLE SCINTILLOMETER

Measurement of soil-gas radon (Rn) concentration is an important param eter in estimating soil Rn potential for a building site. Typically, f ield methods for grab samples (as contrasted with continuous flow syst ems) using a portable alpha-scintillometer only considered Rn-222 (T-1 /2 = 3.8 d) and ignored Rn-220 (T-1/2 = 55 s). Now the calculation per mits the determination of the concentrations of both isotopes with a s ingle series of readings. A sample is collected and within 1 minute is introduced into the counting system. A series of 1 minute counts begi ns immediately and continues for 10 minutes. If high Rn-220 concentrat ions are present, there will be a rapid decay followed by a steady ing rowth of Rn-222 progeny. If very little Rn-220 is present, the ingrowt h will be seen immediately. In either case, a non-linear least square fitting program from Statgraphics is used to obtain both concentration s 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; th e biases did not exceed 15 percent.