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. ²⁵²Cf is sealed in the doubly encapsulated stainless steel container by Ar-arc welding. The inner capsule, with the sealed active element, is imported from Russia integrally.