A neutron source is any device that emits neutrons, irrespective of the mechanism used to produce the neutrons. In some embodiments, the neutron source has a source activity of at least 1E15 Bq, for example, at least 7.15E12 Bq. In some embodiments, the neutron source has a source activity of at least 14 MeV.

Certain isotopes undergo spontaneous fission with emission of neutrons. The most commonly used spontaneous fission source is the radioactive isotope californium-252. ²⁵²Cf and all other spontaneous fission neutron sources are produced by irradiating uranium or another transuranic element in a nuclear reactor, where neutrons are absorbed in the starting material and its subsequent reaction products, transmuting the starting material into the SF isotope. ²⁵²Cf neutron sources are typically ?″ to ?″ in diameter and 1″ to 2″ in length. A typical ²⁵²Cf neutron source emits between 1×10⁷ to 1×10⁹ neutrons per second and has a half-life of 2.6 years.

In some embodiments, any known neutron generator such as a sealed tube neutron generator is used as the neutron source. Suitable neutron generators include a lightweight portable neutron generator, such as the Thermo Scientific MP320 generator or other generators that can produce high energy neutrons. If a neutron generator is used, the neutron target and and proton target may be provided as slabs placed next to the generator instead of two concentric cylinders. The neutron beam travels some distance before leaving the generator. The two slabs can be placed next to the neutron generator window or with a custom made neutron generator can be placed directly after the neutron beam. In any embodiment, a proton-impervious beam stop may be placed downstream of the targets.