Gamma ray measurement of earth formation properties using a position sensitive scintillation detector

Claim 1

A system for measuring properties of earth formations in the vicinity of a well borehole at a plurality of different radial distances from the borehole, comprising: a fluid tight hollow body member sized and adapted for passage through a well borehole and housing therein; a source of gamma rays and means for directing gamma rays from said source outwardly from said body member into earth formations in the vicinity of the borehole; and a position sensitive scintillation detector for detecting gamma rays scattered back into said body member from the earth formation in the vicinity of the borehole, means for collimating said scattered gamma rays onto said detector, said detector comprising scintillation crystal means having a plurality of discrete longitudinally spaced active regions or bins and being longitudinally spaced from said gamma ray source and having a longitudinal length L and two opposite ends and having photomultiplier tubes optically coupled to said opposite ends for providing output voltage signals having voltage amplitudes A and B representative of the intensity of scintillation events occurring in said crystal and impinging at said opposite ends thereof, means separating said bins for selectively attenuating light passing therebetween, and means for combining said output voltage signals A and B according to a predetermined relationship to derive the discrete bin along said length L of each of said scintillation events in said crystal, thereby providing measurements of the gamma ray scattering properties of the earth formations at different radial distances from the borehole.

Claim 2

A system for measuring properties of earth formations in the vicinity of a well borehole at a plurality of different radial distances from the borehole, comprising: a fluid tight hollow body member sized and adapted for passage through a well borehole and housing therein; a source of gamma rays and means for directing gamma rays from said source outwardly from said body member into earth formations in the vicinity of the borehole; and a position sensitive scintillation detector for detecting gamma rays scattered back into said body member from the earth formation in the vicinity of the borehole, means for collimating said scattered gamma rays onto said detector, said detector comprising scintillation crystal means having a plurality of discrete longitudinally spaced active regions or bins and being longitudinally spaced from said gamma ray source and having a longitudinal length L and two opposite ends and having photomultiplier tubes optically coupled to said opposite ends for providing output voltage signals having voltage amplitudes A and B representative of the intensity of scintillation events occurring in said crystal and impinging at said opposite ends thereof, means separating said bins for selectively attenuating light passing therebetween, and means for combining said output voltage signals A and B according to a predetermined relationship to derive the discrete bin along said length L of each of said scintillation events in said crystal, thereby providing measurements of the gamma ray scattering properties of the earth formations at different radial distances from the borehole.