# Can neutrons be ejected from an atom?

In a neutral atom, can neutrons be ejected, and if so, by what (nuclear) process or reaction? I have read Neutron emission and Can a proton be ejected from an atom, but I don't understand how and if that would work for removing neutrons from a heavy atom such as lead-208. Can neutrons be ejected from lead-208 so that it is lead-197, and if not, why?

The typical binding energy per nucleon $$(E_\mathrm B/A)$$ of most nuclides is about $$5{-}8\ \mathrm{MeV}$$. Such values are higher than the released energy of a typical radioactive decay. Therefore, emission of neutrons doesn’t occur during most usual radioactive decay processes.
In order to make a neutron source, you have to find a suitable target (not $$^{208}\mathrm{Pb}$$) and a corresponding nuclear reaction that releases a neutron and that is also energetically favourable, for example $$^9\mathrm{Be}\ (\alpha,\mathrm n)\ ^{12}\mathrm C$$ $$^9\mathrm{Be}\ (\gamma,\mathrm n)\ 2\ ^{4}\mathrm{He}$$ Note that $$^{12}\mathrm C$$ and $$^{4}\mathrm{He}$$ are very stable nuclides with a relatively high binding energy per nucleon so that these reactions can release a large amount of energy, but still you need to irradiate the beryllium targets with high-energy radiation (high-energy $$\gamma$$ radiation of more than $$E=1.665\ \mathrm{MeV}$$ e.g. of $$^{124}\mathrm{Sb}$$ or $$\alpha$$ radiation) to release neutrons.
More important, however, are so-called neutron precursors, e.g. $$^{87}\mathrm{Br}$$ or $$^{137}\mathrm{I}$$, which have a very high decay energy so that the product nuclides ($$^{87}\mathrm{Kr}$$ and $$^{137}\mathrm{Xe}$$, respectively) can get enough energy to make neutron emission possible in the next step. $${}^{87}\mathrm{Br}\xrightarrow[{E_\mathrm{max}=6.83\ \mathrm{MeV}}]{\beta^-}{}^{87}\mathrm{Kr}^*\xrightarrow[\quad]{}{}^{86}\mathrm{Kr}+\mathrm n$$ $${}^{137}\mathrm{I}\xrightarrow[{E_\mathrm{max}=5.89\ \mathrm{MeV}}]{\beta^-}{}^{137}\mathrm{Xe}^*\xrightarrow[\quad]{}{}^{136}\mathrm{Xe}+\mathrm n$$ Such reactions are responsible for the so-called delayed neutrons, which are very important for most nuclear reactors – without this effect, controlling a nuclear chain reaction would be difficult.