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Alpha decay
Intermediate
Emission of a helium nucleus.
A nucleus emits a helium-4 nucleus: ᴬ_Z X → ᴬ⁻⁴_{Z−2}Y + ⁴₂He. Alphas are heavily ionising but stopped by paper.
Uranium-238 → thorium-234.
Energy ~4–9 MeV in discrete lines.
In more detail
Alpha decay emits a helium nucleus from a heavy nucleus, reducing the mass number by four and the atomic number by two. The alpha particle is emitted with a fixed energy determined by the decay.
Real-world uses
- Alpha sources are used in smoke detectors.
- Alpha decay is used in radioisotope power sources.
- Smoke detectors use americium, which emits alpha particles that are detected in an ionisation chamber.
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Frequently asked questions
Are alpha particles dangerous?
Outside the body they are stopped by paper, but they are very harmful if inhaled or ingested.
What is an alpha particle?
A helium-4 nucleus with two protons and two neutrons.
Are alpha particles dangerous outside the body?
They are stopped by a sheet of paper or the outer layer of skin, so they are dangerous mainly if inhaled or swallowed.
Related topics in Atomic & Nuclear Physics
Binding energy per nucleon · Nuclear force · Radioactivity discovery · Beta decay · Gamma decay · Radioactive decay law