20. Ionizing radiation – basic terminology, dose units

Definition of ionizing radiation

Ionizing radiation is energy (particles or waves) that removes electrons from atoms = creating ions.

Types of Ionizing Radiation

• Electromagnetic: X-rays, gamma rays

• Particulate: Alpha, beta particles, neutrons

Direct vs Indirect Ionization

• Direct: By charged particles (e.g. alpha, beta)

• Indirect: By electromagnetic waves (e.g. X-rays, gamma)

Dose

The total energy delivered to body tissue by ionizing radiation.

Absorbed Dose

Amount of energy absorbed per unit mass of tissue.
Unit: Gray (Gy)

Equivalent Dose

Absorbed dose adjusted for radiation type.
Unit: Sievert (Sv)

Equivalent dose = “How damaging is this type of radiation in general?”

Effective Equivalent Dose

Equivalent dose adjusted for organ sensitivity. Reflects overall health risk.

Effective dose = “How damaging is it to the whole body’s health, considering which organs were hit?”

Collective Dose

The sum of the effective doses received by all individuals in a given population
Unit: Man-Sievert (man-Sv)

What Do We Measure in Radiation?

• Activity

• Exposure

• Absorbed dose

• Equivalent dose

Unit of Activity

Becquerel (Bq) = 1 decay/second
Measures how radioactive a material is.

Unit of Exposure

Roentgen (R) or Coulomb/kg (C/kg)
Measures ionization in air (X-rays/gamma).

Unit of Absorbed Dose

Gray (Gy) = 1 joule/kg
Measures energy absorbed by tissue.

Unit of Equivalent Dose

Sievert (Sv) = Gy × Radiation Weighting Factor
Measures biological effect.

Alpha Radiation

• 2 protons + 2 neutrons

• High ionization, low penetration

• Stopped by skin/paper

• Dangerous if inhaled/ingested

Beta Radiation

• Electron (β⁻) or positron (β⁺) emission

• Moderate penetration

• Stopped by plastic/aluminum

Gamma and X-rays

• no mass, no charge

• Electromagnetic radiation

• Low ionization, high penetration

• Blocked by lead/concrete

Neutron decay

• Particle with net zero charge

• Isotope- same element, different mass

• No charge, highly penetrating

• Stopped by concrete or water

Spontaneous decay of radioactive nuclei

• Heavy radioactive element splits into 2 or 3 lighter daughter nuclei

• Emission of different rays and particles can be observed

Difference between radiation and radioactive materials

• Radioactive

  • materials themselves emit ionizing radiation

  • Can remain inside the body if inhaled, ingested, or absorbed

  • e.g. uranium and radon

• Radiation

  • energy in form of particles or electromagnetic waves

  • itself does not remain in the body

  • e.g: alpha particles, beta particles, gamma rays, X-rays.