Dosimetry & Bioassays

Always wear your dosimeter!

A dosimeter is a device that measures occupational radiation exposure. The two main types of personnel dosimeters in use at the UW are Luxel dosimeters and TLD rings.

Luxel dosimeter Luxel dosimeters are optically stimulated luminescence dosimeters (aluminum oxide), usually worn at collar level to monitor whole body dose.
ring dosimeter Ring dosimeters contain thermoluminescent material (lithium fluoride TLDs) and are worn to monitor the hands.

A dosimeter is required if an individual has the potential to exceed 10% of the annual limits for occupational radiation exposure. The potential for exposure depends upon the radiation source (type and quantity of radioactive material or type of x-ray equipment in use), as well as the circumstances of use. The appropriate type of dosimeter is also a function of these circumstances. The Radiation Safety Office reviews each request for dosimetry to ensure that the right personnel monitor is issued for that situation. If you have questions about dosimetry requirements, please consult the Radiation Safety Manual, Section 6 (Personnel Exposure and Monitoring) or call the Radiation Safety Office at 206.543.0463 or email radsaf@u.washington.edu.


Each work area or department where personnel require dosimeters has a person designated as an Area Dosimetry Coordinator (ADC). This person orders dosimeters, distributes them to staff, collects them at the end of the month for processing, and receives monthly and annual dosimetry reports.


Use RSO Form 7, Request for Radiation Worker Dosimetry. This form may be obtained from your ADC. If your workplace does not have an ADC, it is possible that dosimetry is not required in that area. Contact the Radiation Safety Office at 206.543.0463 or email radsaf@u.washington.edu if you have questions about ordering dosimeters.

You should report the loss to your ADC as soon as possible so a spare dosimeter can be issued. Use Missing/Damaged Dosimeter Report(RSO Form15). This form can be filled out on line and printed. Sign and return it to your ADC who will forward it to Radiation Safety. Dosimeters that are not returned in a timely manner may be assessed an administrative fee in accordance with the University of Washington Unreturned Dosimeter Policy. Contact the Radiation Safety Office at 206.543.0463 or email radsaf@u.washington.edu if you have questions about missing dosimeters or our Dosimeter Policy.

Doses from ingested or inhaled radioactive materials cannot be monitored by personnel dosimeters. Instead, a bioassay is used for measuring radionuclide uptake. Please refer to the section on Bioassays for more information about this type of monitoring.

Pregnant radiation workers have the option to reduce their occupational doses. A gestational dose limit of 500 mrem applies to declared pregnant workers. For additional information on exposure to the fetus consult the Radiation Safety Manual, Section 6 (Personnel Exposure and Monitoring). The pregnancy declaration requires a written notification to the Radiation Safety Office (using a simple form). Use RSO Form 9 (Request for Fetal Monitoring) to take advantage of this option. If you wish to keep the pregnancy declaration confidential, request the form directly from the Radiation Safety Office (206.543.0463) or e-mail:radsaf@u.washington.edu and indicate the need for confidentiality; otherwise, your ADC can supply you with a Form 9.

For information on the requirements for bioassays consult the Radiation Safety Manual, Section 6 (Personnel Exposure and Monitoring). The most common type of bioassay is the Thyroid Bioassay, which is required under the following circumstances:

  1. For those individuals who use more than 1 mCi of radioiodine. It is the responsibility of the individual to contact the Radiation Safety Lab (HSB, T561) at 206.543.6328, 206.685.2994, or e-mail: radsaf@u.washington.edu to arrange a bioassay appointment at the lab.
  2. For those individuals who use radioiodine in a laboratory that has ordered or stored 0.5 mCi (500 uCi) or more for one calendar quarter. Radiation Safety staff, who will go to the designated laboratories and perform the required thyroid scans, performs these quarterly bioassays.

An individual (even a non-radioiodine user) may request a bioassay at anytime by calling the RS lab for an appointment (206.543.6328, 206.685.2994 or e-mail:radsaf@u.washington.edu).

Tritium urine analysis bioassays are required for the following individuals:

  1. For anyone working with more than 100 mCi of H-3 in a single use must have a bioassay within one week of that use.
  2. Anyone working with a throughput of more than 100 mCi in a month must have a bioassay once a month. Tritium urine analysis is the responsibility of the user. Please call the Radiation Safety Office at 206.543.0463, 206.543.6328, or 206.685.2994 or email radsaf@u.washington.edu for instructions.