Neutron sources offer neutrons, which are emitted either by the spontaneous fission of some heavy elements, or the (α, n) reaction between some light elements such as Be, B, F and the α particles emitted by the decaying of radionuclides. Attentions should be paid to the external irradiation, the protection means of which including reducing exposure time, increasing exposure distance and using effective shielding materials. Neutron emissions can be stopped by hydrogenous materials such as water, plastic and paraffin. ²³⁸Pu-Be neutron source (for oil field) is prepared by powder metallurgy technique with ²³⁸Pu active element sealed in the Ar-arc welded stainless steel capsule.