If Eqs. 1, 2, and 4 are combined into the form of Eq. 3, a rela- tionship between the net photopeak count rate and the source activity within the soil will result. In addition, if the appropriate detector calibration results are inserted with the appropriate parameters for a given source distribution and the required numerical integration is performed, the desired conversion factor is produced. factor, ° S/NP, : . . . as determined above is in units of The conversion 3 Yfem -sec aera For a specific radionuclide the results can also be given in terms of total activity per unit area, Sos using 2 “f sa 0 zea soeae 8 e (5) oO Another useful conversion factor relates the net photopeak count rate to the average concentration in a given layer of soil. The average concentration per unit volume in the top z centimeters, $7, 1s given by st Vv = +zZ gseVv edz Cat 5011686 (6)