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Adelphi Technology Inc.
2003 E. Bayshore Road
Redwood City, CA 94063

Tel: +1 (650) 474 2750
Fax: +1 (650) 474 2755

Neutron Basics

A neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of elements consist of protons and neutrons. The number of protons in a nucleus is the atomic number and defines the element. The number of neutrons is the neutron number and determines the isotope of the element. For example, the abundant carbon-12 isotope has 6 protons and 6 neutrons, while the very rare radioactive carbon-14 isotope has 6 protons and 8 neutrons.

While bound neutrons in stable nuclei are stable, free neutrons are unstable; decaying in just under 15 minutes. Free neutron beams are obtained from neutron sources by nuclear fission or nuclear fusion.

Until the introduction of Adelphi generators, access to intense neutron sources meant that researchers must travel to specialist neutron facilities like research reactors and spallation sources to work with free neutrons for use in irradiation and in neutron scattering experiments. Now, much of this work can be performed in the researcher’s home lab.

Neutron Generation Overview

Because free neutrons are unstable, they can be obtained only from nuclear disintegrations, nuclear reactions, and high-energy reactions (such as in cosmic radiation showers or accelerator collisions).

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 either deuterium, tritium or a mixture. 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. The DT reaction is used more commonly 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 from the fusion reaction are emitted isotropically (uniformly in all directions). In all cases, the associated He nuclei (alpha particles) are emitted in the opposite direction of the neutron.

In comparison with radionuclide neutron sources, neutron tubes can produce much higher neutron fluxes and monochromatic neutron energy spectrums can be obtained. The neutron production rate can also be controlled.