Proceeding from a short characterization of neutron activation logging and the differences to conventional well logging techniques, the factors which influence the connection between measured value and interesting geological parameter are considered. A formula for the energy distribution of the γ-rays at the detector is given, which involves a single row matrix. Resulting from this, conditions to achieve an optimum measuring effect and principles for the design of a sonde are derived. The peculiarities of the sonde ANGS 42 are: 1) the neutron source is placed at a definite distance above the detector, 2) the automatic control of the energetical position of the discriminator level. For example the accuracy of content determination in fluorite exploration and the factors which influence this determination are discussed. The possibilities of Ca–, Si– and Al-determinations are mentioned as well as the measuring techniques and technological details to improve the accuracy of measurements and to expand the scope of chemical elements to be analyzed.