The main natural source of free neutrons is secondary radiation from cosmic radiation (creation of particles by interactions of cosmic radiation particles with atoms of the earth’s atmosphere). The main sources of neutrons generated artificially are nuclear reactors. Free neutrons have an average lifetime of about 888 seconds (e.g., Mampe et al. 1989a,b: 887.6 ± 3 s) and decay according to

\[n\ {\rightarrow}\ p\ +\ e^{{-}}\ +\ {\bar{v}}\]
(1)

into a proton p, an electron e and an anti-neutrino v̄. Hence, free neutrons must be produced shortly before their use. Besides reactors, where neutrons from nuclear...

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