This topic will cover the basics of radiation, including the different types of radiation, how it is produced, and its characteristics.
Introduction to Radiation – Study Notes
| Term | Definition |
|---|---|
| Radiation | The emission and propagation of energy in the form of particles or electromagnetic waves. |
| Ionizing radiation | Radiation with enough energy to remove tightly bound electrons from atoms, creating ions (e.g., X‑rays, γ‑rays, α‑particles, β‑particles, neutrons). |
| Non‑ionizing radiation | Lower‑energy radiation that does not ionize atoms (e.g., visible light, infrared, microwaves, radio waves, ultraviolet‑A/B). |
| Category | Sub‑type | Typical Sources | Typical Energy Range |
|---|---|---|---|
| Electromagnetic | X‑rays, γ‑rays, UV, visible, IR, radio | X‑ray tubes, radioactive decay, Sun, LEDs | 10 eV – >10 MeV |
| Particle | α‑particles, β‑particles, neutrons, protons, heavy ions | Radioactive nuclei, nuclear reactors, cosmic rays | 0.1 MeV – >100 MeV |
| Acoustic/Mechanical | Ultrasound | Medical imaging transducers | 20 kHz – 1 GHz (energy expressed as pressure) |
Only the first two groups are usually meant when discussing “radiation” in physics and health contexts.
| Concept | Explanation | Units |
|---|---|---|
| Energy (E) | Amount of work that can be done by the radiation. | electron‑volt (eV), joule (J) |
| Frequency (ν) | Number of wave cycles per second (for EM radiation). | Hertz (Hz) |
| Wavelength (λ) | Distance between successive peaks of a wave. | meters (m) |
| Speed of light (c) | Relationship: c = λ·ν (≈ 3.00 × 10⁸ m s⁻¹ in vacuum). | |
| Half‑life (t½) | Time for half of a radioactive sample to decay. | seconds, years, etc. |
| Activity (A) | Number of decays per unit time. | becquerel (Bq = 1 decay s⁻¹) |
| Absorbed dose (D) | Energy deposited per unit mass. | gray (Gy = 1 J kg⁻¹) |
| Equivalent dose (H) | Absorbed dose weighted by radiation type (quality factor Q). | sievert (Sv = 1 J kg⁻¹) |
| Radiation | Primary Interaction(s) with Matter |
|---|---|
| α‑particles | Direct ionization; short range (≈ a few µm in tissue). |
| β‑particles | Ionization and bremsstrahlung; range up to a few mm in tissue. |
| γ‑rays / X‑rays | Photoelectric effect, Compton scattering, pair production (energy‑dependent). |
| Neutrons | Elastic/inelastic scattering with nuclei, neutron capture, (n,γ) reactions. |
| UV‑A/B | Electronic excitation, photochemical reactions (e.g., DNA damage). |
| Visible/IR | Electronic/vibrational excitation, thermal heating. |
*The probability of each interaction is described by a cross‑section (