the particular detector and container combination utilized the linear relationship between potassium chloride concentration and count rate as derived from least squares linear regression analysis yields a calibration constant of 0 0753 as shown in equation 1 below this combination of detector and container is now calibrated and ready for use in the measuring of the potassium chloride concentration of a drilling fluid during actual well drilling operations as the drilling fluid is sampled its gamma radiation is measured the derived calibration constant is utilized to determine depletion in the potassium chloride concentration of the drilling fluid as drilling operations progress by the multiplication of the measured gamma radiation count rate with the derived calibration constant any change in the configuration or size of the container or the use of a new detector will require the recalibration of the apparatus with derivation of a new calibration constant it is an important aspect of the invention to provide adequate shielding of the gamma radiation detector from any external background radiation typically gamma radiation detectors have been shielded by shielding materials forming part of the container itself such as a lead shielding material up to four inches of lead shielding has been found to be necessary under normal laboratory environmental conditions for proper shielding such a container is not readily portable to provide for a lighter weight container that can be more easily transported to the field during well drilling operations applicant utilizes the drilling fluid sample itself as the shielding material rather than utilizing.