The Advantages of Standardizing Radiometric Exploration Measurements, and How To Do It

CIM Bulletin, Vol. 70, No. 778, 1977

A. G. Darnley, Director, Resource Geophysics and Geochemistry Division, Geological Survey of Canada, Ottawa

The fact that there are standard units of mass, distance and time is taken for granted. It is also accepted that the type of instrument used to measure one of these parameters is irrelevant to the way the measurement is reported. Some geophysical parameters, for example magnetic field strength and gravity, have generally accepted units, the gamma and milligal, which are defined in SI terms. These units are used irrespective of the equipment used to -measure them. By contrast, the situation for the measurement of natural radioactivity is, in practice, confused, unsatisfactory and not conducive to efficient exploration. There are at least six different ways of reporting measurements of radioactivity made with different designs of field scintillation counters, and several of these are specific to the particular instrument on which a measurement is made. With gamma-ray spectrometry, the problem is theoretically simpler because the reason for using a spectrometer is to distinguish radioactivity caused by potassium, uranium and thorium. Most instrumentation now on the market is suitable for calibration, so that it is quite possible to report results in terms of the concentration of each of these elements. Unfortunately, this is not done as generally as might be supposed. The adoption of common measuring units, and standardization of instrumentation to read in terms of these units, has many advantages. Measurements are no longer purely relative, with a limited basis for comparison. Measurements can be gathered in different places at different times with different instruments, and compared systematically. Meaningful compilations can be made. Instrument sensitivities can be established, and malfunctions recognized more readily. There can be greater confidence in identifying small, but possibly significant, differences in the radioactivity of individual litholoaies. These benefits can apply equally to ground, airborne and borehole measurements of radioactivity. A Consultants Committee of the International Atomic Energy Agency has recently prepared recommendations on Reporting Methods and Calibration in Uranium Exploration, including the definition of a new unit for the measurement of total (undiscriminated) radioactivity, and procedures for the calibration of all types of ground, airborne and borehole equipment used for the measurement of natural gamma radiation. In part, these procedures follow those already established by the Geological Survey of Canada. Under its new Uranium Program, it is the intention of the Geological Survey to complete, in the near future, the variety of facilities required to permit the implementation of the IAEA recommendations, and to provide as -much assistance as possible to encourage their general adoption in Canada.

Keywords: Exploration, Radiometric exploration, Uranium, Geophysics.