Specifications

Sonde Dimensions

Sonde length 0.7 m

Sonde diameter 38 mm

Sonde weight 4.0 Kg

Why use it?

Natural gamma is generally ran as a standard with other sondes to assist in the correlation and alignment of structures.

It record's the naturally occurring remnant decaying isotopes in the formations, which assists in deriving the lithologies for the different rock types.

Principle Of Operation

This sonde uses a Sodium Iodide scintillation crystal coupled to a photomultiplier to detect natural gamma radiation. The scintillation crystal has external dimensions of 50mm long by 28mm diameter.

The range of energies detected by the sonde is from 65KeV (the lower threshold of the sonde) and up to 2.6MeV, the highest naturally occurring radiation, encompassing a large spectrum.

The most common decay series elements detected are:

                                                Uranium                 : Hard rock formations

                                                Thorium                 : Sands, sandstone's

                                                Potassium             : Clay, Shales

For U₃O₈ logging the sonde can be calibrated at the certified AMDEL calibration pits in Adelaide to enable accurate % of Uranium to be recorded. Models AM1, 2, 3 &7 are used for the calibration, at the AMDEL pits Borehole size compensation curves can also be derived.

A radium 226, test source is used to monitor instrument drift/variation when calibrated for Uranium readings.

Natural gamma can be detected through rod strings RC & Diamond, as well as cased boreholes. There will be a damping effect when logging in these environments, however the lithology trace can still generally be used to determin formation boundaries.

Instrumentation can be operated at speeds of up to 15m/min.

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