Natural Background Radiation
We encounter radiation naturally - cosmic radiation filters down through the atmosphere, terrestrial radiation comes up from the earth in rocks and building materials, and trace amounts of radiation are found in what we eat, drink, and breathe. On average, Americans are exposed to about 3 mSv (or 300 mrem) of natural radiation in a year, though this varies from place to place. For example, we are exposed up to .01 mSv (or 1 mrem) per hour during airplane flights.
Radiation at UCSF
Radiation is a useful tool in research and clinical applications. X-rays can help image structures inside the body, small amounts of radioactive material can be injected to help identify internal processes, and large amounts of radiation can treat serious conditions such as cancer. However, significant radiation exposure can damage skin, the lens of the eye, or even increase the risk for cancer. Whenever radiation is considered, it is important to ensure that the benefits outweigh the risks and use reasonable precautions to limit unnecessary exposure.
The goal of the Radiation Safety Program is to keep radiation exposure risks "as low as reasonably achievable" (or ALARA). This is accomplished by using the minimum amount of radiation needed for the desired result, and by the appropriate use of
- Time: The amount of radiation exposure is directly related to the time exposed to the radioactive source. Reduce exposure by limiting the time near radiation to only what is necessary.
- Distance: Doubling the distance from a source of radiation reduces exposure by 75%. Increase distance from the radiation source whenever possible.
- Shielding: Use appropriate shielding for the type of radiation. Lead protective garments or drapes can reduce exposure during x-ray imaging. Higher energy x-rays or gamma rays can be decreased by walls of thicker lead or concrete. Beta radiation can be blocked by a centimeter of Lucite. Alpha radiation is stopped by a sheet of paper or a few centimeters of air.