Environmental radiation comes from both natural and human-made sources. Natural sources like cosmic rays, terrestrial radiation, and radon gas make up about 80% of our average annual exposure. The rest comes from medical procedures, industrial applications, and nuclear energy.

Understanding these sources is crucial for assessing radiation risks and protecting public health. Natural radiation levels vary based on location and geology, while human-made sources can change over time due to technological advances and regulatory changes.

Natural Radiation Sources

Cosmic and Terrestrial Radiation

• Cosmic radiation originates from space consists of high-energy particles that interact with Earth's atmosphere producing secondary radiation
  • Intensity increases with altitude and latitude
  • Contributes approximately 13% of average annual radiation dose
• Terrestrial radiation emanates from naturally occurring radioactive materials in the Earth's crust including uranium, thorium, and their decay products
  • Varies based on local geology (higher levels in granite-rich areas)
  • Accounts for about 20% of average annual radiation exposure

Radon and Internal Radiation Sources

• Radon gas a decay product of uranium serves as the most significant natural source of radiation exposure for most populations
  • Contributes approximately 50% of average annual radiation dose
  • Concentrations vary dramatically between buildings and rooms due to soil composition and construction
• Radioactive isotopes in food and water contribute to internal radiation exposure through ingestion
  • Potassium-40 found in bananas, potatoes, and other foods
  • Carbon-14 present in all living organisms
  • Together account for about 10% of average annual radiation dose

Anthropogenic Radiation Sources

Medical and Industrial Applications

• Medical procedures constitute the largest source of anthropogenic radiation exposure
  • Diagnostic X-rays (chest X-rays, mammograms)
  • Nuclear medicine (PET scans, thyroid treatments)
  • Radiation therapy for cancer treatment
  • Account for 15-20% of average annual radiation exposure in developed countries
• Industrial applications utilize radioactive sources that can potentially lead to environmental contamination
  • Industrial radiography for non-destructive testing of materials
  • Well logging in oil and gas exploration
  • Sterilization of medical equipment and food products

Nuclear Energy and Weapons

• Nuclear power plants and fuel cycle facilities release small amounts of radioactive materials during normal operation
  • Potential for larger releases during accidents (Chernobyl, Fukushima)
  • Contribute less than 0.1% to average annual radiation dose for most populations
• Nuclear weapons testing particularly atmospheric tests conducted in the mid-20th century has contributed to global environmental radiation levels
  • Global fallout has decreased over time but still present in environment
  • Contributes less than 1% to average annual radiation dose for most populations

Natural vs Anthropogenic Radiation

Relative Contributions

• Natural sources typically account for the majority (about 80%) of the average person's annual radiation exposure
  • Radon gas alone contributes to approximately 50% of the average annual radiation dose
  • Cosmic and terrestrial radiation combined account for about 33%
• Anthropogenic sources contribute the remaining 20% of average annual radiation exposure
  • Medical procedures represent the largest anthropogenic source (15-20%)
  • Nuclear power, weapons testing, and industrial sources contribute less than 1% combined

Variability Factors

• Relative contributions can vary significantly based on individual factors
  • Lifestyle choices (living at high altitudes, frequent air travel)
  • Medical history (number and type of medical imaging procedures)
  • Geographical location (local geology, proximity to nuclear facilities)
• Occupational exposure can significantly alter individual radiation doses
  • Airline crew members receive higher cosmic radiation doses
  • Nuclear power plant workers may have increased exposure
  • Medical professionals working with radiation (radiologists, nuclear medicine technicians)

Radiation Levels: Variations

Geographical Variations

• Cosmic radiation exposure increases with altitude and latitude
  • Higher doses at mountain elevations and polar regions
  • Lower doses at sea level and equatorial regions
• Terrestrial radiation levels vary based on local geology
  • Higher levels in areas rich in granite or uranium-bearing rocks (parts of Brazil, Iran)
  • Lower levels in sedimentary rock areas
• Radon concentrations vary dramatically between locations
  • Influenced by soil composition, building materials, and ventilation
  • Can differ significantly even between adjacent buildings

Temporal Variations

• Anthropogenic radiation levels may show temporal variations
  • Short-term spikes related to nuclear accidents (Chernobyl, Fukushima)
  • Long-term changes due to weapons testing or changes in medical practices
• Natural radiation levels can exhibit long-term variations
  • Climate change potentially altering distribution of natural radionuclides
  • Geological events (earthquakes, volcanic eruptions) affecting radon release
• Long-term environmental monitoring programs track changes in radiation levels
  • Essential for identifying potential sources of contamination
  • Provide data for assessing long-term trends and health impacts