Alpha and beta particles are two distinct types of ionizing radiation emitted during radioactive decay, and they differ in composition, charge, mass, penetrating power, and how they're produced.
Composition and charge
- An alpha particle consists of two protons and two neutrons bound together—essentially a helium-4 nucleus (He²⁺). It carries a charge of +2.
- A beta particle is a high-energy, high-speed electron (beta-minus) or positron (beta-plus), carrying a charge of −1 or +1 respectively.
Mass
- Alpha particles are relatively heavy, with a mass of about 4 atomic mass units.
- Beta particles are much lighter—roughly 1/7,300th the mass of an alpha particle—since an electron's mass is only a tiny fraction of a proton's or neutron's mass.
Origin
- Alpha decay occurs in heavy, unstable nuclei (like uranium, radium, or plutonium) as they shed mass to become more stable, converting the parent element into one with an atomic number reduced by 2 and mass number reduced by 4.
- Beta decay happens when a neutron converts into a proton (emitting an electron and an antineutrino) or a proton converts into a neutron (emitting a positron and a neutrino), changing the atomic number by 1 without changing the mass number.
Penetrating ability and speed
- Alpha particles travel relatively slowly and have very low penetrating power—they can be stopped by a sheet of paper or even the outer layer of human skin, though they're highly ionizing and dangerous if inhaled or ingested.
- Beta particles move much faster (close to the speed of light in some cases) and penetrate further, requiring materials like aluminum foil or plastic to block them. They are less densely ionizing than alpha particles but still pose radiation hazards.
Deflection in fields Because of their differing mass and charge, alpha and beta particles deflect differently in electric and magnetic fields—alpha particles deflect less due to their greater mass, while beta particles deflect more sharply because they're lighter.