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Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Doubly-charged helium ions (He2+) are essentially equivalent to which of the following particles?
Beta particles
Alpha particles
Gamma rays
Protons
Alpha particles
A doubly‑charged helium ion, He2+, is a helium atom that has lost both its electrons, leaving only the nucleus consisting of two protons and two neutrons – exactly an alpha particle.
A doubly‑charged helium ion, He2+, is a helium atom that has lost both its electrons, leaving only the nucleus consisting of two protons and two neutrons – exactly an alpha particle.
It is like a car stripped of its wheels; only the core chassis remains, which is the same as the chassis used elsewhere.
He²⁺ = Alpha (He → He‑4 nucleus).
q=+2e — charge of an alpha particle
mα≈6.64×10−27kg — mass of an alpha particle
In radioactive decay, an alpha particle is emitted as the He2+ nucleus. Because the ion retains the same mass number (4) and charge (+2e) as the emitted alpha particle, they are indistinguishable in physical behavior.
Alpha particles are He2+ nuclei (2 protons, 2 neutrons).
They carry a +2 elementary charge and have low penetration power.
High ionising power useful in smoke detectors.
Poor penetration; stopped by a sheet of paper.
Smoke detectors (ionisation chamber)
Radiotherapy for certain cancers
| Feature | He^{2+} | Proton |
|---|---|---|
Charge | +2e | +1e |
The mass of an alpha particle is about 4 atomic mass units.
Option A (beta) is an electron (−1e), Option C (gamma) is neutral photon, Option D (proton) has +1e charge.
B is correct — doubly‑charged helium ions are identical to alpha particles, the helium‑4 nucleus.
Recall that alpha particles have charge +2e and mass 4 u, whereas beta particles are electrons (−1e) and gamma rays are mass‑less photons.