The method and calculation formulas to determine the chance coincidence in the ^220Rn coincidence measurement are introduced in this paper. The poisson distribution is introduced to correct the chance coincidence. The relative deviation of the true coincidence between the method and the Giffin is within 5% after the correction of the cohance coincidence. The measurement of ^220Rn is done by comparative measurement with RADT. The results shows that ^220Rn can be measured by the method with a relative deviation of 14%. Mean while, for the ^220Rn flow regime is difficult to meet the condition of ...
