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Small-source Density

Stringent legislation on the transport and handling of radioactive materials increasingly prevents use of conventional density logging probes. The small-source density probe provides calibrated and borehole-compensated density logs at sensible logging speeds using a very low activity 60Co gamma source that may not require a radiation licence in certain territories.

Principle of Measurement:

The probe contains a detachable collimated gamma source and two high-sensitivity scintillation gamma detectors. The detectors are protected against direct radiation from the source or via the borehole by extensive heavy- metal shielding. The active windows of source and detector are maintained in contact with the borehole walls by a motorised caliper arm. The detected backscattered gamma radiation depends on the formation density. The probe includes a third gamma detector mounted remotely from the source for ‘stripping’ natural background radiation.


  • Compensated density output directly in engineering units (g/cc)
  • Tungsten shielding reduces borehole influence on measurement
  • Separate short-spacing detector for accurate bed-boundary location


  • Bulk density
  • High-resolution density (HRD)
  • Caliper
  • Natural gamma



  • Lithology
  • Density and porosity
  • Correlation with other logs
  • Bed thickness and boundary location
  • Ash and moisture content in coal


  • Rock strength and elasticity parameters (with sonic log)
  • Detection of weathered or fractured zones


  • Location of aquifer and aquitard
  • Location of cement cavities behind casing


Diameter: 51mm
Weight: 19kg
Temperature: 0-70⁰C (extended ranges available)
Max. pressure: 20MPa
Density range: 1.1- 2.9g /cc
Caliper range: 50 – 250mm

Operating Conditions

  • Borehole type: open-hole, water-filled
  • Qualitative measurements are  possible in air-filled boreholes.

Sales Information

I002017 Small-source density probe

Download Small-source Density sheet


...Practical Innovation with Global Service & Support...

Robertson Geologging Ltd., 2017

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