Radiation Dosimetry

A well-functioning dosimetry program is essential for a safe operation and for compliance with applicable federal and state regulations. The University radiation dosimetry program is described in detail in Procedures 3.1/3.1.1.

Click picture for a larger viewClassification of Dosimeters: There are four methods of radiation dosimetry at the University as follows:

  • External dosimeters (whole body) are used to measure deep dose equivalent expressed in units of rem or Sv.
  • External dosimeters such as ring dosimeters are used in cases where external exposure to hands or other specific organs are likely to exceed whole body exposure.
  • The internal dosimetry (bioassay) program covers a potential intake of radionuclides.
  • Direct reading external dosimeters are used for short term exposure at high radiation areas.

Classification of Individuals Addressed by the Dosimetry Program: The large majority of employees and students at the University are not exposed to ionizing radiation and thus, are not covered by the dosimetry program. The remainder of individuals is classified into three groups as follows:

Required to wear dosimeters:

  • Adults who are likely to receive an annual effective dose equivalent of 100 mrem (1 mSv) - included is the committed effective dose equivalent of internally deposited radionuclides
  • Minors or pregnant women who are likely to receive an annual dose equivalent of 50 mrem (0.5 mSv)

May request a dosimeter:

  • Adults who are likely to receive a radiation exposure, but their annual exposure is likely to be less than an effective dose equivalent of 100 mrem (1mSv)
  • Minors and pregnant women who work in the vicinity of a radiation source, but are unlikely to receive an annual dose equivalent of 50 mrem (0.5mSv)

Assessment Process: It is recognized that a great deal of judgment is required to place an individual in a group and to apply a specific method of monitoring. These decisions are made by the Radiation Safety Officer as recommended by the Radiation Safety Committee based on the following criteria:

  • Exposure history of individual and similar workers
  • Work habits
  • Nature of the work
  • Quantity of radioactive materials and/or strength of radiation source     
  • Other relevant parameters

The placement of an individual is reassessed as needed by the Radiation Safety Committee as recommended by the Radiation Safety Officer.

Pregnant Workers: University policy relies upon the ALARA principle, thus reducing the necessity for a special policy for pregnant women. However, there is a recognition that a pregnant worker may require specific information to make an informed decision. The Fetal Protection Program is described in detail in Procedure 1.4.

  • To be considered under the Pregnant Worker policy, a woman must declare her pregnancy in writing and provide other relevant information , e.g., approximate date of conception or delivery.
  • EHS will provide counselling if desired.
  • The worker will be assigned a monthly fetal monitoring dosimeter.
  • In the event of elevated edposures, the RSO may seek reassignment of duties.

Exposure Reports: The Radiation Safety Officer reviews exposures on a regular basis. Subsequently, high or unusual exposures are reported to the Radiation Safety Committee. All monitored individuals included receive an annual exposure report.

Enforcement of External Dosimetry Program: External dosimeters will be provided to required individuals on an appropriate basis i.e., monthly or quarterly. All individuals in this group are required to promptly return the dosimeters. A delay by more than one month in returning the dosimeter without a written explanation may be considered a violation of University policy and may lead to the revocation of authorization to use radioactive materials or a monetary penalty.

Individuals that are assigned dosimeters due to voluntary request are required to comply with all policies governing monitored individuals. This group is also expected to return the dosimeter promptly. Failure to return a dosimeter by more than one month may be considered a violation of University policy.

Internal Dosimetry Program:

  • Applies to anyone utilizing 1 mCi or more of unsealed radioiodine or 100 mCi or more of unsealed tritium.
  • Applies to anyone involved in an accident or spill who become personally contaminated.

Enforcement of Internal Dosimetry Program: The method and the frequency of bioassay depends upon the nature including the half-life of the radionuclide of concern. Once the frequency of bioassay is established, the enforcement follows the external dosimetry enforcement by replacing the month with the appropriate interval (e.g. 14 days).