In addition to its primary role as a lithological or clay indicator, a natural gamma measurement is frequently used as the basis for establishing correlations between boreholes and to ensure accurate depth matching between different logging runs made in the same borehole. For these reasons, many LIM probes provide this measurement as an additional log along with other parameters.

The GRT38 probe provides a solution for cases where only a basic, total counts natural gamma log is required and also provides a borehole fluid temperature measurement useful for correcting certain other logs.

Based on a ø25 x 50 mm NaI(Tl) scintillation crystal detector coupled to a high-performance photomultiplier tube, the probe boasts excellent sensitivity (±1.2 cps / API unit) and provides a high quality final result.

For clients requiring this additional parameter, the probe can be factory fitted with a casing collar locator (CCL) detector.

Contact us to get a quote or request more information.


  • diameter : 38 mm
  • Length : 1 180 mm
  • Weight : 3kg
  • Max. operating temperature: 70°C
  • Max. operating pressure : 200 bar

  • Natural gamma detector: ø25 x 50 mm NaI(Tl) crystal
  • Temperature range : 0 to 65°C
  • resolution : 0.001°C

  • CCL detector
  • Calibration : factory calibration in API units

  • Dry or fluid-flled borehole
  • Open or cased borehole


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