Neutron logs are a radioactive exploration method that uses neutrons to interact with rocks and wells around the well to detect gamma radiation, drilling profile analysis, finding valuable deposits, and the ways of studying the quality of oil well engineering. 

Neutron γ logging tool is the use of gamma detectors to measure the strength of the natural gamma radioactivity, according to the inherent radioactive strength of underground geological deposits to determine the instrument measurement depth.

 

Neutron γ logging tool is in the neutron field and would interact with the neutron to decrease the spectrum resolution and interfere with the measurement. A shield must be placed between the two in order to prevent neutrons from emitting neutrons directly expose to the neutron tip. The neutron shielding is much more complex than the simple gamma-ray shielding. We should consider the shielding of fast neutrons, thermal neutrons, and the gamma ray effects of shielding materials and neutrons. 

 

 

The neutron source used in well logging needs to be developed with small volume, high strength, high controllability, high safety, high temperature resistance and high pressure resistance. Therefore, tungsten heavy alloy has become the top choice to shield neutron γ logging tool, for it has advantages of high density, small size, good corrosion resistance and high radiation absorption capacity, etc.

 

Through the experimental study, when shielding material thickness is less than 5.5cm, graphite and ethylene produce less gamma rays. With the increase of the shielding thickness, photon fluence of Pb decreased fastest, gamma rays and neutron effects rarely, followed by copper, iron, tungsten, graphite and tin, etc. The shielding effect of tungsten is the best, according to its shielding effectiveness on fast neutron and the production of the gamma ray. When tungsten thickness is10cm, it can shield about 90% of neutron. Therefore, tungsten shielding material can successfully solve the neutron shielding problem of short distance detector in multi-detector.