For accurate measurements of radon/thoron concentrations with a gas_through and static time_delay method using a single scintillation cell,a theoretical study of radon/thoron calibration factors was carried out and the influences of sampling flow rate on cali_bration factors were discussed. The theoretical values of calibration factors were calculated by theoretical formulas and compared with the experimental values after standard calibra_tion. The results show that the experimental values are in good agreement with the theoreti_cal values,and the deviations are less than 5%. The accuracy of e...