A WELL LOGGING TOOL WITH AN ACCELERATOR NEUTRON SOURCE

摘要

In the illustrative embodiments of the invention disclosed, a neutron porosity well logging tool includes a D-T neutron accelerator and a fast-neutron monitor for monitoring accelerator output. The monitor comprises an organic scintillator having a characteristic dimension that is small relative to the average range of gamma ray-induced electrons that would produce high pulses of magnitudes comparable to those resulting from recoil protons produced by source neutrons, while it is large relative to the average range of such recoil protons. The scintillator is coupled via a photomultiplier to a pulse height discriminator circuit that passes pulses in the higher-energy flat portion of the spectrum. Consequently, the neutron source monitor produces a signal that is proportional to the intensity of the neutron source.