Definition - What does Neutron Log mean?
Neutron Log is a neutron porosity log which measures the concentration of hydrogen ions in a hydrocarbon formation. Neutrons are emitted from the log from a source at the bottom of the tool. When the neutrons collide with the hydrogen nuclei, they deflect back and slow down. These slowed down neutrons are detected and an apparent neutron porosity log is obtained.
Petropedia explains Neutron Log
Lane Wells ran the first commercial Neutron Logs in 1945. The main purpose of a Neutron Log is to interpret the tool signals that help in characterizing the hydrocarbon formation information in a reservoir. It contains a radioactive or isotopic source, most often americium beryllium which after reaction emits high energy neutrons. As more and more neutrons enter the hydrocarbon formation, they collide with the hydrogen nuclei of the formation and slow down and the nuclei emit a high energy gamma ray. These deflected slow neutrons are detected by detectors placed at the bottom of the tool.