where D is the absorbed dose rate in nGy/h and AU, ATh and AK are the activity concentrations of 238U, 232Th and 40K, respectively.
The annual effective dose equivalent for adults from outdoor terrestrial gamma radiation is obtained by taking into account the conversion coefficient of 0.7 Sv/Gy from the gamma absorbed dose rate in air (D), also including the outdoor occupancy factor of 0.2 [1], as follows: