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The dual-neutron probe provides a calibrated borehole-compensated neutron porosity measurement in mud-filled open holes. It is the probe of choice for quantitative formation-fluid studies. A single-detector neutron probe is also available for qualitative porosity logging under most borehole conditions including through steel or plastic casing and drill-pipe.

Principle of Measurement:

The dual-neutron measurement uses two ³He proportional detectors and a detachable, sealed 241Am-Be neutron source. Fast neutrons emitted by the source are scattered and slowed to thermal levels principally by hydrogen in the formation. The ratio of the neutron flux reaching the near and far detectors depends on the hydrogen index and porosity. Use of dual detectors and a ratio method provides a porosity measurement which is independent of hole diameter.


  • Real-time porosity measurement
  • Compensation for borehole diameter


  • Compensated porosity (Dual-neutron tool only)
  • Neutron (raw counts)
  • Count ratio (NRAT)
  • Natural gamma
  • Option: Casing-collar locator (CCL)


  • Minerals/Engineering Water
  • Lithology identification
  • Location of aquifer and aquitard
  • Shale content
  • Fracture analysis in coals
  • Correlation between open and cased-hole logs
  • Strata correlation between wells


Dual Neutron Single Neutron
Diameter: 60mm 38mm
Length of sonde: 1.94m 2.08m
Weight: 18.8kg 8kg
Temperature: 0-70⁰C (extended ranges available)
Max. pressure: 20MPa
Range: 0 to 60% apparent sandstone porosity

Operating Conditions

  • Borehole type: open/cased, water-filled
  • Qualitative measurements are possible in air-filled boreholes
  • Centralisation: excentralised with bowspring

Sales Information

I002029 Dual-neutron probe with natural gamma
I002030 – includes CCL I002026 Single-neutron probe
I002026 Single-neutron SP/SPR probe
I015483 – includes natural gamma and CCL


Download Neutron sheet


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

Robertson Geologging Ltd., 2017

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