Pulsed neutron decay tool for measuring gamma radiation energy spectra for fast neutron inelastic collisions and thermal neutron capture events

摘要

A well logging tool in accordance with the present invention is provided for emitting neutron bursts, and determining inelastic energy spectra and thermal neutron capture cross sections during a single logging pass over a well depth interval. Inelastic energy spectra are determined, in part, by measuring exponential decay rates for thermal neutrons capture events that occur during decay periods which extend for at least several thermal neutron lifetimes following each of the neutron bursts, and by using the measured exponential decay rates to project from thermal neutron capture spectra detected during the decay periods a value for thermal neutron capture components of the total energy spectra detected during neutron burst periods.