5.2.2 The Three Types of Nuclear Emission
We will look at how α‑particles, β‑particles and γ‑radiation are deflected by electric and magnetic fields. Think of each type as a different “ball” that reacts differently when it hits a field.
α‑Particles (Helium Nucleus)
Analogy: Imagine a heavy bowling ball (mass ≈ 4 u) that carries a +2 charge. It is heavy and strongly charged.
- Electric field: deflected strongly in the positive direction.
- Magnetic field: deflected in a circular path, radius small because of its mass and charge.
- γ‑radiation: not deflected at all (neutral).
Mathematically, the electric force is \$F = qE\$ and the magnetic force is \$F = qvB\$. Because \$q=+2e\$, the deflection is larger than for β‑particles.
β‑Particles (Electrons or Positrons)
Analogy: Think of a light tennis ball (mass ≈ 1 u) that can be either negatively or positively charged.
- Electric field: deflected in the direction of its charge (negative → opposite to field).
- Magnetic field: deflected in a circular path, radius larger than α‑particles because of smaller charge‑to‑mass ratio.
- γ‑radiation: no deflection.
Because β‑particles have a smaller charge-to-mass ratio, they are deflected less by a magnetic field compared to α‑particles.
γ‑Radiation (High‑Energy Photons)
Analogy: Imagine a beam of invisible light that carries no charge and no mass.
- Electric field: no deflection.
- Magnetic field: no deflection.
- γ‑radiation interacts only with matter (photoelectric effect, Compton scattering).
Summary Table of Deflections
| Particle | Electric Field | Magnetic Field | Deflection Size |
|---|
| α‑particles | Strong, positive direction | Circular, small radius | Large |
| β‑particles | Depends on charge sign | Circular, larger radius | Medium |
| γ‑radiation | None | None | None |
Examination Tips
- Remember that α‑particles are the most massive and most strongly charged, so they are deflected the most.
- For β‑particles, note that the deflection direction depends on whether it is an electron (negative) or positron (positive).
- State that γ‑radiation is not deflected by electric or magnetic fields.
- Use the formula \$r = \frac{mv}{qB}\$ to calculate the radius of curvature in a magnetic field; remember that a larger \$q\$ or smaller \$m\$ gives a smaller radius.
- When answering, clearly label the direction of deflection (e.g., “toward the positive plate” or “to the left of the beam path”).