Neutron generator
Neutron generators are neutron source devices which contain compact linear accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deuterium, tritium, or a mixture of these two isotopes into a metal hydride target which also contains deuterium, tritium or a mixture of these isotopes. Fusion of deuterium atoms (D + D) results in the formation of a He-3 ion and a neutron with a kinetic energy of approximately 2.5 MeV. Fusion of a deuterium and a tritium atom (D + T) results in the formation of a He-4 ion and a neutron with a kinetic energy of approximately 14.1 MeV. Neutron generators have applications in medicine, security, and materials analysis.
Thousands of such small, relatively inexpensive systems have been built over the past five decades.
Small neutron generators using the deuterium (D, hydrogen-2, 2H) tritium (T, hydrogen-3, 3H) fusion reactions are the most common accelerator based (as opposed to isotopic) neutron sources. In these systems, neutrons are produced by creating ions of deuterium, tritium, or deuterium and tritium and accelerating these into a hydride target loaded with deuterium, tritium, or deuterium and tritium. The DT reaction is used more than the DD reaction because the yield of the DT reaction is 50–100 times higher than that of the DD reaction.
D + T → n + 4He En = 14.1 MeV
D + D → n + 3He En = 2.5 MeV
Neutrons produced by DD and DT reactions are emitted somewhat anisotropically (non-uniformly in all directions) from the target slightly peaked in the forward (along the axis of the ion beam) direction. The anisotropy of the neutron emission from DD and DT reactions is introduced by the fact that the reactions are isotropic in the center of momentum coordinate system (COM) but the isotropy is lost in the transformation from COM coordinate system to laboratory system. In both cases, the associated He nuclei are emitted in the opposite direction of the neutron (in COM) as dictated by the conservation of momentum.
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