In this paper

a method for total-count γ-ray measurement of radon in activated carbon is presented

with correction for decay and time delay for the measurement based on the decay of radon and its progeny. Simulation of the total-counts of γ-rays from radon-absorbed activated carbon was performed. The results show that the time-dependent calculated curve of γ-ray total-counts agrees well with the measured one. The front part of the curve

where the counts increase first and decrease later

is the time delay for the measurement. The duration of delayed measurement is closely related to the duration of radon absorbed by activated carbon

but it has nothing to do with the radon concentration. And the longer the adsorption duration

the shorter is the time delay. Then

the counts follow the function of e-0.000125 t

which is also independent of the concentration of radon absorbed by activated carbon.