NEUTRON SOURCESDOE-HDBK-1019/1-93Reactor Theory (Neutron Characteristics)NP-02Page 4Rev. 0Neutron Sources SummaryIntrinsic neutron sources are sources of neutrons from materials that are inthe reactor for other purposes such as fuel, burnable poison, or moderator.Installed neutron sources are materials or components placed in the reactorspecifically 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 andfree neutrons.Boron-11 mixed with the fuel undergoes an alpha-neutron reactionand 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 fragmentsand free neutrons.Beryllium-9 undergoes an alpha-neutron reaction (alpha from thedecay of plutonium, polonium, or radium) and becomes carbon-12.Beryllium-9 undergoes a gamma-neutron reaction (high energygamma from decay of antimony-124) and becomes beryllium-8.Many startup sources of this type use antimony and beryllium because after activation withneutrons the radioactive antimony becomes an emitter of high energy gammas. The photoneutronsources of this type are constructed somewhat differently from the (,n) types. One designincorporates a capsule of irradiated antimony enclosed in a beryllium sleeve. The entire assemblyis then encased in a stainless steel cladding. A large reactor may have several neutron sources ofthis type installed within the core.SummaryThe important information in this chapter is summarized below.
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