Physical Agents of Disease: Ionizing and Non-Ionizing Radiation

Definition: Radiation is energy traveling through space, including alpha particles, beta particles, gamma rays, X-rays, and uncharged neutrons.
Ionizing Radiation: Radiation with sufficient energy to remove tightly bound electrons from atoms, creating ions. It is used in electric power generation, cancer treatment, and manufacturing.
Non-ionizing Radiation: Radiation with enough energy to move or vibrate atoms but not enough to remove electrons. Examples include sound waves, visible light, and microwaves.

Anthropogenic (Man-Made): Includes medical X-rays and radiation therapy (accounting for approximately $40\%$ of exposure), consumer products, and nuclear power plant leaks.
Nuclear Facilities and Accidents: Notable incidents include the Three Mile Island accident ( $1979$ ) and the Chernobyl disaster in Ukraine ( $1986$ ).
Natural Sources: Cosmic rays from outer space and terrestrial radiation from geologic formations.
Uranium and Radon: Uranium is a common crustal element found in North America, Africa, and Australia. Radon, a decay product of uranium and radium, is a colorless, toxic Class A carcinogen that can seep into homes.

Radioactivity: The spontaneous emission of radiation from unstable nuclei. Types include Alpha ( $2$ protons, $2$ neutrons), Beta (proton decays to neutron), and Gamma (high-speed penetrating energy).
Units of Radioactivity: Becquerel ( $Bq$ ) ( $1\,\text{disintegration/second}$ ) and Curie ( $Ci$ ) ( $3.7 \times 10^{10}\,\text{disintegrations/second}$ ).
Absorbed Dose: Measured in Gray ( $Gy$ ) or Rad ( $1\,Gy = 100\,rad$ ).
Dose Equivalent: Measured in Sievert ( $Sv$ ) or Rem ( $1\,Sv = 100\,rem$ ).
Exposure: Measured in Roentgen ( $R$ ) or Coulomb/kilogram ( $C/kg$ ).

Acute Effects: High-level exposure causes tissue burns and radiation sickness (nausea, hair loss, and weakness).
Stochastic Effects: Long-term low-level exposure increases the probability of carcinogenesis and genetic damage ( $DNA$ changes).
Exposure Limits: The National Council on Radiation Protection (NCRP) sets an annual occupational limit of $5\,rem$ . The average US background exposure is $360\,mrem$ .
Management: Strategies include washing contaminated skin, internal absorption reduction using binding agents, and organ saturation using Potassium Iodide to protect the thyroid.

Extremely Low Frequency (ELF): Radiation from power lines ( $50$ to $60\,Hz$ ). Research on its link to cancer remains inconsistent and non-definitive.
Radiofrequency (RF) and Cell Phones: Cell phones transmit at $900$ to $1800\,MHz$ . Epidemiologic research generally does not support a clear relationship with morbidity.
Ultraviolet (UV) Radiation: Categorized into $UVA$ ( $315$ to $400\,nm$ ), $UVB$ ( $280$ to $315\,nm$ ), and $UVC$ (< 280\,nm). $UVB$ is the most harmful but also essential for Vitamin D synthesis.
UV Index: A daily risk forecast scale from $1$ (minimal) to $11+$ (extreme).
LASER: Coherent light beams categorized into four classes based on the risk of eye injury.
Infrared and Visible Light: Infrared can cause thermal injury and corneal damage, while high-frequency blue visible light ( $400$ to $500\,nm$ ) poses a risk for retinal injury.