Dual scintillation detector, single photomultiplier density logging system

Claim 1

A gamma ray density well logging system comprising: a fluid tight hollow sonde sized and adapted for passage in a well borehole and having disposed therein a source of medium energy gamma rays and means for selectively irradiating preferred portions of earth formations in the vicinity of a well borehole with said gamma rays, first scintillation detector means longitudinally spaced from said source and having first phosphorescent decay characteristics, second scintillation detEctor means longitudinally spaced from said source and said first scintillation detector means and having second, substantially different phosphorescent decay characteristics, means situated between said detector means for optically coupling said first and second scintillation detector means and effectively shielding said detectors from each other with respect to gamma radiations, means optically coupled to said first and second scintillation detectors for generating first and second voltage pulses in response to scintillations occurring in said first and second detectors, said first and second voltage pulses having substantially different shape characteristics due to the difference in said first and second phosphorescent decay characteristics, means for transmitting said voltage pulses from said sonde to the surface of the earth and means for separating said first and second voltage pulses from each other on the basis of their substantially different shape characteristics.