Introduction
Ionizing radiation interacts with human tissues by depositing energy, leading to ionization and excitation of atoms and molecules. These interactions can damage DNA and cells, causing both immediate and long-term health effects. Dosimetry provides the framework for quantifying exposure and risk.
Dosimetric Quantities
- Absorbed Dose (D):
- Energy imparted by radiation per unit mass of tissue.
- Formula:
- Unit: gray (Gy).
- Power of Absorbed Dose (PD):
- Rate of energy deposition in tissue.
- Unit: Gy/s.
- Exposure (X):
- Ionization produced in air by X-rays or γ-rays.
- Unit: coulombs per kilogram (C/kg).
- Power of Exposure (Px):
- Rate of exposure delivery.
- Unit: (C/kg)/s.
- Equivalent Dose (H):
- Accounts for type of radiation.
- Formula:
- Unit: sievert (Sv).
- WR: radiation weighting factor (e.g., 1 for γ, β; 20 for α).
- Power of Equivalent Dose (PH):
- Rate at which equivalent dose is delivered.
- Unit: Sv/s.
- Effective Dose (E):
- Considers sensitivity of tissues (tissue weighting factor WT ).
- Formula:
- Unit: sievert (Sv).
Sources of Ionizing Radiation
Natural Sources
- Cosmic radiation (higher at altitude).
- Terrestrial radiation from soil, rocks.
- Radon gas (largest contributor to natural background).
- Naturally radioactive isotopes (K-40, C-14).
Technogenic (Artificial) Sources
- Medical: X-ray imaging, CT, nuclear medicine, radiotherapy.
- Industrial: nuclear power, radiography, material testing.
- Fallout: from past nuclear tests, accidents.
- Consumer products: luminous dials, smoke detectors.