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Alpha particles are

Asked in CBSE AIPMT 1999 · Nature of alpha, beta and gamma radiation

Answer: (4) doubly ionised helium atoms

Step-by-step solution

An α-particle is the nucleus ⁴₂He: two protons and two neutrons, with no orbital electrons.

A neutral helium atom carries two electrons around that nucleus.

Stripping both electrons away is double ionisation, and what remains is exactly the bare nucleus.

So an α-particle is a doubly ionised helium atom, of charge +2e and mass number 4.

Why the other options are wrong

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