Method and apparatus for measuring neutron characteristics of material surrounding a borehole

A method for logging the formations surrounding an earth borehole, comprising: pulsedly irradiating said formations with discrete bursts form a source of high energy neutrons; detecting radiations emanating from said irradiated formations at a detector spaced from said source; measuring said detected radiations during first and second time intervals following a burst from said source; generating time-separated electrical pulses indicative of said detected radiations during a third fixed time duration interval following a subsequent burst from said sources; and controlling automatically the starting time of said third measurement interval in accordance with the said measurement from said first and second time intervals