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University of Colorado Denver

Environmental Health and Safety, University of Colorado Denver

Radiation Safety Training

Radiation Exposure and Dosimetry

Background Radiation

Apart from the amount of radiation a worker may receive while performing work, they will also be exposed to radiation because of the very nature of our environment. All individuals are subject to some irradiation even though they may not work with radioactive substances. This common source of exposure is often referred to as background radiation.

Exposure, Dose, and Dose Equivalent

Ionizing radiation transfers enough energy to remove electrons from the atoms in matter. This ionization is the basis for the biological effects in cells or tissue.

Remember that the dose is the energy deposited per mass while the equivalent dose is the biological effect in Roentgen Equivalent Man (rems) or Sieverts (Sv). Also, the Roentgen (R) is a unit of exposure of electric charge collected per mass but is only defined for photons in air. Dose equivalent is a useful quantity since it relates the biological effect to different types of radiation, and different cell types, tissues and organs.

Internal and External Sources

There are two potential primary exposure types connected with work involving radioisotopes: external and internal exposure to radiation.

  • External exposure is due to radioactive sources external to the body.
  • Internal exposure is generally due to an uptake of radioactive materials into the body through one of the following routes of entry: inhalation, ingestion, or skin contact.

Your occupational dose record is required to sum the doses from internal and external sources.

Attenuation - Shallow and Deep Dose

Ionizing radiation is attenuated as it passes through the living tissue of the human body. Deeper tissues typically receive lower dose than shallower tissues from external sources of radiation (the exception to this is higher energy gamma).

Dosimetry systems such as personnel monitors report the estimated doses received from external sources at two key depths commonly specified as Shallow Dose Equivalent (SDE) and Deep Dose Equivalent (DDE). These are reported on your dose record, so it is helpful to conceptually understand the SDE and DDE.

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