Neutron Sources Summary

NEUTRON SOURCES DOE-HDBK-1019/1-93 Reactor Theory (Neutron Characteristics) NP-02 Page 4 Rev. 0 Neutron Sources Summary Intrinsic neutron sources are sources of neutrons from materials that are in the reactor for other purposes such as fuel, burnable poison, or moderator. Installed neutron sources are materials or components placed in the reactor specifically for the purpose of producing source neutrons. Examples of intrinsic neutron sources are listed below. Spontaneous fission of heavy nuclides in fuel, such as uranium-238, uranium-235, and plutonium-239, results in fission fragments and free neutrons. Boron-11 mixed with the fuel undergoes an alpha-neutron reaction and becomes nitrogen-14. Deuterium present in the reactor coolant undergoes a gamma- neutron reaction and becomes hydrogen-1. Examples of installed neutron sources are listed below. Spontaneous fission of californium-252 results in fission fragments and free neutrons. Beryllium-9 undergoes an alpha-neutron reaction (alpha from the decay of plutonium, polonium, or radium) and becomes carbon-12. Beryllium-9 undergoes a gamma-neutron reaction (high energy gamma from decay of antimony-124) and becomes beryllium-8. Many startup sources of this type use antimony and beryllium because after activation with neutrons the radioactive antimony becomes an emitter of high energy gammas. The photoneutron sources of this type are constructed somewhat differently from the ( ,n) types. One design incorporates a capsule of irradiated antimony enclosed in a beryllium sleeve. The entire assembly is then encased in a stainless steel cladding. A large reactor may have several neutron sources of this type installed within the core. Summary The important information in this chapter is summarized below.