Forest He-3 Tubes

The neutron capture of He-3 may be represented by the reaction below

[math]n + He^3 \rightarrow p + H^3[/math]

About 764 keV of energy is liberated in this nuclear reaction and distributed between the final products according to their masses. Because the proton is about a factor of 3 lighter than Tritium (H^3) , it will have more kinetic energy by about a factor of 3 (about 573 keV). This liberated proton can ionize other He-3 atoms via the reaction

[math]p+He^3 \rightarrow p + He^3(+) + e^-[/math]

The same proton will ionize several He-3 atoms when dissipating the 573 keV kinetic energy.

The Tritium (H^3) can also ionize the gas but due to its higher mass it does not travel as far (shorter range) as the proton and makes a smaller contribution to the ionization signal.

reference: J. W. Leake, "Nuclear Instruments and Methods", Vol. 63, page 329, 1968).