Exposure Limits

The annual limit for employees who work with radiation is the lower of:

  1. The total effective dose equivalent = 5,000 millirem (0.05 Sv); or
  2. The sum of the deep dose equivalent and the committed dose equivalent to any individual organ or tissue (other than the lens of the eye) = 50,000 millirem (0.5 Sv).

The annual limits to the lens of the eye, to the skin, and to the extremities are:

  1. Eye dose equivalent = 15,000 millirem (0.15 Sv)
  2. A shallow dose equivalent = 50,000 millirem (0.5 Sv)

Non-Occupational Exposure Limits (Members of the Public)

Each user of radioactive material shall conduct operations so that:

  1. The dose in any unrestricted area from external sources does not exceed 2 millirem (0.02 mSv) in any one hour.
  2. The total effective dose equivalent to individual members of the public from a licensed operation, exclusive of the dose contribution from a licensee’s disposal of radioactive material into sanitary sewerage, does not exceed 100 millirem (1 mSv) in any year.

Declared Pregnant Workers Exposure Limits

The increased sensitivity of rapidly dividing cells makes the human embryo and fetus particularly susceptible to injury from exposure to ionizing radiation. For this reason, regulations require that exposure to the fetus during the gestation period not exceed 500 millirem (5 mSv). More information on this topic can be found under Recommended reading for pregnant female radiation workers.

Any radiation worker who is pregnant or believes that she may be pregnant should contact DRS and review the recommended reading. All inquiries will be confidential. The individual must complete a Declaration of Pregnancy Form for the lower limits to apply. If a written declaration of pregnancy is not submitted, then the worker’s dose continues to be controlled under the normal dose limits for radiation workers. A declaration of pregnancy can be withdrawn at any time.

For the type of radiation work performed at the University of Illinois, it is rarely necessary to recommend reassignment or changes to job duties to reduce exposure.

The dose must be approximately uniform throughout the pregnancy. Care shall be taken so that no more than 50 millirem (0.5 mSv) be received during any one month during a declared pregnancy. Efforts shall be made to avoid substantial variation above the uniform monthly exposure rate to a declared pregnant woman.

If, by the time the pregnant woman informs DRS of the estimated date of conception, the dose to the embryo/fetus has exceeded 450 millirem (4.5 mSv), the limit for the remainder of the pregnancy shall be 50 millirem (0.5 mSv).

If the pregnant woman has not notified DRS of her estimated date of conception, the dose to the fetus shall not exceed 50 millirem (0.5 mSv) per month during the remainder of the pregnancy.

Exposure Limits for Minors

The annual occupational dose limits for minors are 10 percent of the annual occupational limits specified for adult workers. 

Personnel Dosimetry

The use and type of personnel dosimetry is determined by the activities and functions the individual performs. By regulation, any person who receives or is likely to receive more than 10 percent of the maximum permissible dose or who enters a high radiation area must be provided with and must wear personnel monitoring devices.

DRS assigns dosimetry when certain quantities and radionuclides are used. Specifically, the use of >10 mCi of P-32 requires the user to wear both an extremity (commonly referred to as a “ring”) and a whole-body dosimeter. At usage levels ≤10 mCi of P-32, dose assessments will be performed to evaluate the need for dosimetry. Dosimetry is not issued for individuals working with weak beta-emitting radionuclides such as H-3, C-14, P-33, and S-35.

DRS evaluates use of dosimetry for other radionuclides and quantities on a case-by-case basis.

To enroll in dosimetry services, complete a Dosimetry Request Form and return it to DRS.

Whole body dosimeters, or badges, monitor exposure to the whole body and should be worn between the neck and the waist, usually on the front of the body.

Finger ring dosimeters monitor radiation exposure to the hands and fingers. These dosimeters may be worn on any finger and should normally face the palm side of the hand. Finger rings must be worn under gloves to prevent them from becoming contaminated.

Every person with assigned dosimeters must wear the badges and/or ring dosimeters when working with sources of ionizing radiation.

The dosimeter reading is the legal record of an individual’s occupational radiation exposure. Therefore, dosimeters must be worn only by the individual to whom it is assigned, must not be tampered with or experimentally irradiated, and must not be used to measure radiation exposure received as a medical patient.

When not being worn, dosimeters must be stored in a location where they will not be exposed to radiation.

Dosimeters are collected monthly or quarterly by DRS personnel and sent to a vendor for processing.  Dosimeters must be made available for this exchange to occur.

If a dosimeter is lost, discontinue radiation-related activities and contact DRS. Individuals who have lost a dosimeter must provide information to DRS personnel so that an assessment of their radiation exposure can be performed. DRS will order a replacement dosimeter. 

Bioassays

Bioassays are used to determine types, concentrations, quantities, or locations of personal uptake of radioactive materials into the body. A baseline (before first use) bioassay and another within 24 to72 hours following each use of the quantities specified are required for the following isotopes:

  • Users of unbound radioactive iodine (typically I-125 or I-131) in quantities of ≥1 mCi on a bench top or in quantities ≥10 mCi in a fume hood require thyroid bioassays. They are performed using a hand-held scintillation probe and survey meter;
  • Tritium bioassays are required when a person uses >100 mCi of H-3 without using a fume hood. They are performed by condensing water from exhaled air followed by liquid scintillation counting of the activity in the sample.

Additional bioassays may be required for personnel on a case-by-case basis as determined by DRS.

Personnel Exposure Records

DRS maintains exposure records for all monitored personnel. Annual reports of exposure are always available to the wearer and a notice is sent advising them to review their exposure report annually.

At the request of a worker, DRS shall furnish their exposure report. The report is furnished within 30 days from the time the request is made, within 30 days of termination of employment, or within 30 days after the individual’s dose has been determined, whichever is later.

Last Update: 10/1/2020
Updated By: kohl3