To reduce the time for measuring radon concentration in soil by passive accumulation method, a rapid method has been studied. The method can provide related parameter values that fitted from unbalanced result by least square method and then get the balanced radon concentration. On account of above conditions, a rapid measuring instrument for radon concentration in soil has been researched. Measured results show that the relative deviation between the fitting values and the balanced values is below 7%, measuring time is shorten more than 3...