Patent ID: 8598510

Claim:
A downhole instrument for estimating density of sub-surface materials, the instrument comprising: a neutron source; an initial inelastic gamma ray detector configured to measure initial inelastic gamma rays generated by a reaction of neutrons output from the neutron source with a surrounding sub-surface material; a near detector for detecting backscattered inelastic gamma rays, the near detector located farther from the neutron source than the initial inelastic gamma ray detector; a far detector for detecting backscattered inelastic gamma rays, the far detector located farther from the neutron source than the near detector; and an electronics unit coupled to each of the source monitoring detector, the near detector and the far detector, the electronics unit configured for receiving a first detection signal corresponding to the initial inelastic gamma rays detected by the initial inelastic gamma ray detector, a second detection signal corresponding to backscattered inelastic gamma rays detected by the near detector and a third detection signal corresponding to backscattered inelastic gamma rays detected by the far detector, and compensating at least one of the second detection signal and third detection signal based on the first detection signal.