Composition: Beta radiation consists of high-speed electrons () or positrons () emitted from the nucleus. These particles are much smaller and lighter than alpha particles.
Properties: They carry a charge of (electron) or (positron). Their ionizing power is moderate—less than alpha but more than gamma.
Penetration: Beta particles have a moderate range, traveling several meters in air. They can penetrate skin but are stopped by a few millimeters of aluminum or plastic.
Composition: Unlike alpha and beta, gamma radiation is not a particle but a high-energy electromagnetic wave (photon). It has no mass and no electric charge.
Properties: Because it is uncharged, it has the lowest ionizing power. It does not interact as frequently with atoms, allowing it to pass through most materials without being absorbed.
Penetration: Gamma rays are highly penetrating and have an infinite range in air. Their intensity is only significantly reduced by dense materials like several centimeters of lead or meters of concrete.
| Property | Alpha () | Beta () | Gamma () |
|---|---|---|---|
| Nature | Helium Nucleus | Electron/Positron | EM Wave |
| Charge | or | ||
| Mass | High (4 amu) | Very Low | Zero |
| Ionizing Power | Very High | Moderate | Low |
| Penetration | Low (Paper) | Medium (Aluminum) | High (Lead) |
The Inverse Rule: Always remember that penetration and ionization are inversely related. If a question asks why alpha is the least penetrating, the answer is because it is the most ionizing (it loses energy faster by interacting with more atoms).
Shielding Thickness: Be careful with Beta radiation; it is stopped by aluminum, but only if the aluminum is a few millimeters thick. Thin foil may not be enough.
Detection Logic: If a source's count rate drops significantly when paper is introduced, it contains alpha. If it drops only when aluminum is added, it contains beta. If it requires lead to drop, it contains gamma.
Mass of Gamma: A common mistake is assigning mass to gamma rays. They are photons (light energy) and have zero rest mass.
Beta Origin: Students often think beta electrons come from the electron shells. In reality, they are emitted from the nucleus when a neutron decays into a proton and an electron.
Range in Air: Do not assume all radiation travels the same distance. Alpha is limited to roughly cm, while Gamma follows the inverse square law and can travel effectively infinite distances in a vacuum.
