Which process results in emission of a helium nucleus (alpha particle)?

• A. Alpha decay
• B. Beta decay
• C. Electron capture
• D. Positron emission

Answer: (A)

Emitting a helium nucleus means the nucleus ejects an alpha particle, which is a helium-4 nucleus made of 2 protons and 2 neutrons. This type of decay is called alpha decay. It typically occurs in very heavy nuclei and leaves the daughter nucleus with its atomic number decreased by 2 and its mass number decreased by 4. The other processes involve emitting particles other than an alpha particle: beta decay emits an electron (beta-minus) or a positron with neutrinos, and electron capture removes an orbital electron and emits a neutrino. None of those produce a helium nucleus.