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Exposure Monitoring Overview

Learn about dosimetry services for radiation workers at UC San Diego.

Employees working with radioactive materials are monitored for radiation exposure with dosimetry badges or rings provided by Environment, Health & Safety (EH&S).

You may be monitored for external or internal exposure, depending on the nature and source of the radiation you work with.

Do you need dosimetry?

  • YES if you use greater than 1 mCi per experiment of a gamma or high-energy beta emitter
  • NO if you only work with low-energy beta emitters such as H-3, C-14, S-35, or P-33
  • MAYBE if you use radiation-producing machines
  • NO if you only use radiation-producing machines remotely

How to request dosimetry

External exposure monitoring

External exposure is monitored with a device that absorbs radiation over a period of time. The device, called a dosimeter, is usually a badge or ring worn by the radiation worker. Dosimeters are periodically analyzed by Environment, Health & Safety (EH&S) and the data is used to calculate the worker's radiation exposure.

The dosimetry program manager reviews all dosimetry data and investigates any unusual exposures. EH&S reports the exposure data to the principal investigator. The report should be posted in the lab or otherwise made available to affected employees.

Internal exposure monitoring

Other methods of determining exposure must be used when radioactive material is inhaled, ingested, or absorbed into the body.

A bioassay is a means of determining internal exposure through analysis of body fluids (in vitro) or direct measurement (in vivo). An example of an in vitro bioassay is a urinalysis. An example of an in vivo bioassay is a thyroid scan, a procedure in which the amount of radiation present is determined by holding a detector directly to the thyroid gland.

Bioassay services

A baseline bioassay should be completed prior to performing experiments that require internal exposure monitoring according to the criteria below.

You need bioassay services if you work with any of the following:

  • H-3 – Have your urine assayed every 2 weeks if more than 100 mCi of a volatile form of H-3 is used per month. EH&S will report positive analytical results to you as soon as results are available.
  • Volatile iodine – Participate in the thyroid monitoring program if you use more than 10 mCi of volatile iodine per month. Monitoring frequency depends on the specific isotope of iodine:
    • I-123 – At least 6 hours after, but within 2 days of a procedure.
    • I-125 – At least 6 hours after, but within 30 days of a procedure.
    • I-131 – At least 6 hours after, but within 5 days of a procedure.
    • Performing multiple iodinations A single bioassay is acceptable, as long as the time from the first iodination to the time of the bioassay doesn't exceed the limits listed above.

Employees who want a bioassay even though they're not required to, or because they suspect an uptake during a large spill, can contact EH&S Radiation Safety, (858) 822-2494.

Bioassays are performed at the EH&S Services Lab. An appointment isn't necessary.

  • Location: University Center 301-B, corner of Myers and Gilman Drive,
    adjacent to Parking Lot 408 (find it on UCSD's MapLink)
  • When: 1 - 4:30 p.m., weekdays

If you need to come by at another time, call (858) 534-6418 to confirm a technician will be available.

Notice: Refer to the Radiation Safety Manual (PDF) (Word file) for a detailed description of UCSD's radiation safety program.