Title: Dual spectra well logging system and method

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Abstract: A well logging system and method in which a transmitter in a borehole has at least two radiation detectors sensing either the same condition or two different conditions relating to the earth's formation traversed by the borehole and providing data pulses corresponding in number and peak amplitude to the sensed condition. The transmitter also includes a reference pulse source and circuitry for combining the reference pulses with each set of data pulses to provide combined pulse signals. Each combined pulse signal is sampled at difference times by a sampling circuit which provides pulses of opposite polarity whose amplitudes correspond to the maximum amplitude pulses occurring during sampling periods. The pulses from the sampling means are conducted to surface electronics by a single conductive path such as the inner conductor and the shield of an armored coaxial cable. The surface electronics includes a pulse separation circuit which separates the pulses by polarity. Processing circuits process the separated pulses to provide records of at least two spectra. The invention is of particular utility as embodied in a nuclear logging system.


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