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Radiation Monitoring

The Nuclear Regulatory Commission (NRC) and Minnesota Department of Health regulations require that all individuals who work in areas where personal radiation monitoring is required, must receive radiation protection training prior to using sources of ionizing radiation.   Therefore, training documentation is a prerequisite to obtaining a radiation monitoring dosimeter.

Radiation Dose received by individuals must be maintained as low as reasonably achievable within the radiation dose limits specified by the NRC regulations, and University license condition.

The following is a description of personnel monitoring methods, and procedures for the measurement of radiation doses received by individuals using sources of ionizing radiation.

Methods of Monitoring

1.   External Dose Assessment:  Personal Monitoring Devices

The following are three types of external personal monitoring devices (dosimeters) commonly used at the University.

  • Thermo-Luminescent Dosimeter (TLD) Body Badges:
    Used primarily for monitoring the radiation dose to the trunk of the body.
  • TLD Rings: Used primarily for monitoring radiation dose to the hands and wrist.
  • Film Badges: A monthly body dosimeter used to monitor exposure of declared pregnant employees.

Personal radiation monitoring dosimeters do not protect individuals from the effect of radiation, but only record the radiation dose an individual has accumulated.

2.   Internal Dose Assessment:   Bioassay

When quantities of radioactive material used by personnel presents a potential for internal contamination, or in the event of a radioactive material spill, the Radiation Protection Division (RPD) will require the necessary bioassay procedure to determine the quantity of the internal disposition and the resulting dose if any.

All bioassay procedures are performed by the Department of Environmental Health and Safety, or by persons or organizations approved by the RPD.  RPD will maintain radiation dose records on all personnel requiring bioassay for assessment of possible internal deposition.

In general the following three bioassays procedures may be used.

  • Urine Analysis:  Will be performed on any individual who uses more than 100 mill-Curies (mCi) of tritiated water, gas or sodium borohydrade, or more than 10 mCi of 3H-Labeled nucleotides per experiment within one week.   If the above quantities are used routinely, a weekly urine analysis (bioassay) is required.
  • Thyroid counts:  Performed on any individual who uses 125I and 131I (Iodine 125, 131) in procedures where volatilization is likely (e.g. protein labeling, column separation, dialysis) within one week following the procedure.   For continuing operations of the above procedures, monthly thyroid counts are required.
  • Whole Body Count:  Required when appreciable internal contamination is suspected or when the potential for internal contamination warrants the procedure.
How to Apply for, and Obtain a Radiation Monitoring Device

  • Application request cards of appropriate radiation dosimeters for assessment of personnel radiation dose are available from the UMD Environmental Health and Safety Office, 31 DAdB, 726-7273.
  • Completed request cards should be sent to the RPD at the address listed on the request card.
  • Personnel radiation dosimeters are not necessary for individuals who use 3H, 14C. 35S, 33P, 45Ca or other low energy beta emitters, because these radioisotopes present little or no external radiation exposure potential.  For 32P Users, dosimetry is required only when the activity of the isotope used is at or above 0.5 mCi, and a TLD Ring is also required if the activity is at or above 1 mCi.  Questions on when a personal dosimeter is required should be referred to the Radiation Protection Division (612) 626-6002.
  • The UMD EHS-Office will have replacement dosimeters, and will be responsible for returning all exposed dosimeters to the RPD on the designated monthly or quarterly change schedule.
  • Individual dosimeter holders are responsible for returning their dosimeters on the scheduled change date.  Failure to do so may result in a financial penalty issued by the RPD.
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