19. Basic concepts, quantities and units in radiation protection. Sources of human exposure.

Basic concepts, quantities and units in radiation protection. Sources of human exposure.

Radiation protection (radioprotection) involves measures and principles aimed at protecting humans from the harmful effects of ionizing radiation while allowing its beneficial uses in medicine, industry, and research.

1. Basic Concepts

• Ionizing Radiation: Radiation with enough energy to remove tightly bound electrons from atoms, creating ions. Examples: X-rays, gamma rays, alpha particles, beta particles.
• Non-Ionizing Radiation: Radiation that cannot ionize atoms but may cause heating or other effects (UV, microwaves, radio waves).
• Exposure: Contact of humans with ionizing radiation. Can be external (from outside the body) or internal (from inhaled, ingested, or absorbed radionuclides).
• ALARA Principle: “As Low As Reasonably Achievable” – minimize radiation dose while achieving the required objective.
• Deterministic effects: Appear above a threshold; severity rises with dose (e.g., burns, cataracts).
• Stochastic effects: Can occur at any dose; probability rises with dose, severity constant (e.g., cancer, mutations).

2. Quantities and units in radiation protection

Radiation protection aims to minimize harmful effects of ionizing radiation while allowing its beneficial uses. The key quantities are:

• Activity (A): Measures the rate of radioactive decay.
• Unit: Becquerel (Bq) = 1 decay per second.
• Absorbed Dose (D): Amount of energy deposited by radiation in a unit mass of tissue.
• Unit: Gray (Gy) = 1 joule/kilogram.
• Equivalent Dose (H): is the radiation dose absorbed by tissue, adjusted for the type of radiation to reflect its biological effect.
• Unit: Sievert (Sv) = 1 joule/kilogram × radiation weighting factor.
• Effective Dose (E): Equivalent dose adjusted for the sensitivity of different organs/tissues.
• Unit: Sievert (Sv) – shows total body risk.
• Exposure (X): measures the amount of ionization produced by X-rays or gamma rays in air.
• Unit: Coulomb per kilogram (C/kg).

A radiation weighting factor (WR) is a number used to represent how biologically damaging a type of radiation is compared to X-rays or gamma rays.

3. Sources of Human Exposure

1. Natural (Background) Radiation:

• Cosmic Radiation: From the sun and outer space.
• Terrestrial Radiation: From radioactive elements in soil, rocks, water (uranium, radon).
• Internal Radiation: From naturally occurring radionuclides in the body (potassium-40, carbon-14).

1. Artificial (Man-Made) Radiation:

• Medical: X-rays, CT scans, nuclear medicine, radiotherapy.
• Occupational sources: Workers in nuclear power plants, radiology labs, or industries using radiography and irradiators.
• Other sources like: Smoke detectors (contain americium-241, emit alpha particles)

4. Hygienic / Protective Principles

• Time: Minimize time exposed to radiation.
• Distance: Maximize distance from radiation source.
• Shielding: Use appropriate barriers (lead, concrete) to absorb or reduce exposure.