Small-Source Density Probe

Stringent legislation on the transport and handling of radioactive materials increasingly prevents use of conventional density logging probes. The small-source density probe provides high-quality calibrated and borehole-compensated density logs at sensible logging speeds using a very low strength nuclear source that does not require a radiation licence in many territories.

PRINCIPLE OF MEASUREMENT
The probe contains a small 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 firmly in contact with the borehole walls by a motorised back-up arm that also provides a borehole caliper measurement. Gamma radiation from the source is backscattered by the formation (Compton effect) and reaches the two detectors where the relative count-rates provide a measure of formation bulk density. The probe includes a third gamma detector mounted remotely from the source to allow ‘stripping’ of natural background radiation.