A pulsed neutron source irradiates an earth formation. The irradiation produces NSUP16/SUP from OSUP16/SUP in a fluid in the borehole, and the gamma rays produced by the subsequent decay of NSUP16/SUP are detected by a plurality of spaced apart detectors. The count rates of the detectors are accumulated over a time sampling interval to produce temporal signals. Processing of the temporal signals using correlation, differentiation and/or semblance techniques is used for determination of the flow velocity of one or more fluids in the borehole.
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