Nuclear methods for logging geological boreholes are used in the hydrocarbon and coal industries, in ore mining, and in water resource exploitation. The well-fitting detector is introduced into the borehole by means of a widlass installed on a vehi­cle. The detected signals are transferred to the measuring instrument located on the surface of cables (Figure 11.29).

Three types of nuclear borehole measurements exist:

• Measuring the natural radiation in each layer.

• Tracking radiation excited with sealed radiation sources.

• Methods using radiotracers introduced into boreholes.

An excitation radiation source can be a sealed gamma source, sealed neutron source, or neutron generator. According to the type of the measured radiation, natu­ral gamma logging, gamma-excited gamma-density logging, neutron detection, and NAA are distinguished. Methods applying open radioisotopes belong to tracer techniques.

Figure 11.29 shows depth distribution of the natural gamma radiation in an exploration of coal mine prospecting. Coal spots located among sandstone and marl layers represent higher gamma intensities.

A great benefit of nuclear borehole techniques is that they also serve data on the chemical composition of penetrated stones and then can be executed in natural
conditions where other methods are not successful. At the same time, their draw­back is that they are more labor-intensive and require complicated measuring instruments and other equipment.

Further Reading

Foldiak, G. (1986). Industrial Application of Radioisotopes. Akademiai Kiado, Budapest. Charlton, J. S. (1986). Radioisotope Techniques for Problem-Solving in Industrial Process Plants. Leonard Hill. Glasgow and London.

Rozsa, S. (1979). Nuklearis me’re’sek az iparban. Muszaki Konyvkiado, Budapest.

Baranyai, L., and Ivicsics, F. (1990). A talajviz aramlasi sebesse’ge’nek meghatarozasa. (Determination of flowing rate of groundwater.). Viziigyi Kozlemenyek 32 (4): 399—400. Lapkiado Vallalat, Budapest.