Nuclear reactions are either fission (when an atomic nucleus is split into two lighter ones) or fusion (when two nuclei are combined into a heavier one). You can demonstrate both of these with a hobbyist setup.
Fission is easiest since radioactive materials can be found in small quantities in everyday objects. Smoke detectors contain around 0.2 milligrams of americium-241, some camping gas lanterns are coated with about 250mg of thorium-232, and gun sights that glow in the dark have about 1.2 micrograms of tritium (hydrogen-3).
All of these are radioactive and if you could combine enough of them, you might be able to make a breeder reactor, which uses neutrons emitted from one source to convert thorium-232 into the more radioactive uranium-233.
This is what David Hahn, a boy scout from Michigan, tried to do in 1994. He didn’t get past the neutron generator stage before he came to the attention of the authorities though, and it’s doubtful whether his setup would ever have reached the point of generating actual, useful power.
To turn nuclear fission into a functioning reactor, you need a way to slow down and control the neutrons so that the fission reaction is fast enough to be self-sustaining, but not so fast that it becomes a runaway critical reaction.
This is a delicate balancing act and difficult to achieve in a small reactor. You also need adequate shielding and cooling to keep everything safe.
Modern ‘microreactors’ are still the size of a shipping container and generate in the range of five megawatts of electricity – definitely too much for a garden reactor.
Fusion reactors are also possible at home, using an electric field to accelerate deuterium (hydrogen-2) ions together, fusing them into helium-3. This produces a cool purple plasma, but it isn’t a useful reactor either since the energy to power the electric field is much higher than the useful energy from fusion.
This article is an answer to the question (asked by Tim Hurst, Sheffield) 'Could I build a nuclear reactor in my shed?'
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