The helium nucleus emitted from an unstable atom is called?

• A. Alpha radiation
• B. Beta radiation
• C. Gamma radiation
• D. X-ray radiation

Answer: (A)

Alpha decay is the process where an unstable nucleus ejects a particle that is two protons and two neutrons, which is a helium-4 nucleus. Because the emitted particle is precisely a helium nucleus, this radiation is called alpha radiation. It’s a relatively heavy, positively charged particle that travels only short distances in matter before being stopped. Beta radiation would be the emission of a fast electron or positron from the nucleus, not a helium nucleus. Gamma radiation is high-energy electromagnetic radiation released from the nucleus after particle emission, not the ejection of a nucleus itself. X-ray radiation refers to photons from electronic transitions, again not the nucleus being expelled. So the helium nucleus emitted corresponds to alpha radiation.