External Exposure

Personnel monitoring devices (whole body dosimeters, extremity dosimeters, pocket dosimeters, etc.) are provided by the EHS through the Radiation Safety Office to measure an individual’s radiation exposure to gamma, energetic beta and x-ray sources. The standard monitoring device is issued as a clip-on badge or ring badge bearing the individual assignee’s name, date of the monitoring period and a unique identification number. The dosimeters are provided, processed and reported through a commercial service company that meets current requirements of the National Institute of Standards and Technology National Voluntary Laboratory Accreditation Program (NVLAP).

Radiation protection regulations and UNC-CH policy require that appropriate personnel monitoring equipment be provided to individuals who:

  1. Are likely to receive a radiation dose in any calendar quarter in excess of 10 percent of:
    1. 5 rems, total effective dose equivalent, to the whole body;
    2. 15 rems, eye dose equivalent, to the lens of the eyes;
    3. 50 rems, shallow dose equivalent, to the skin or to each of the extremities.
  2. Are less than 18 years of age and are likely to receive a radiation dose in any calendar year in excess of 10 percent of;
    1. 0.5 rems to the whole body;
    2. 1.5 rems to the lens of the eyes;
    3. 5 rems to the skin or to each of the extremities.
  3. Have declared a pregnancy or planned pregnancy;
  4. Enter a High or Very High Radiation Area (exposure to greater than 100 millirems in any one hour);
  5. Operate analytical x-ray devices (both monthly ring and whole body badges required, at the discretion of the RSO);
  6. Meet the issuance criteria as assessed by the Radiation Safety Office.
Authorized Users must complete and submit the Lab/Radiation Worker Registration Form for each individual who may work with radiation sources. This form provides for the basic information regarding training and experience and personnel monitoring needs. Initial personnel monitoring decisions will be based on this information. Further evaluations, and re-evaluations, will be made through radiation employee registration updates, application reviews, personnel monitoring reports, high dose investigations, surveys and individual interviews by responsible Radiation Safety staff members.

In general, personnel monitoring devices will be exchanged on the appropriate frequency for individuals needing personnel monitoring as specified in the REQUIREMENTS section above.

Personnel monitoring devices may be exchanged quarterly when less frequent and/or smaller exposures are anticipated. Experience has shown, for example, that quarterly exchanges are appropriate for operators of dental x-ray machines, many sealed sources and most laboratory radiation workers.

Personnel monitoring devices will not normally be issued to individuals who work solely with low energy beta emitters such as H-3, C-14 and S-35 or very small quantities of radioactive material such as I-125 in-vitro kits.

  1. Radiation restricted area under such conditions that an occupational radiation dose in excess of 10 percent of the specified calendar year limits may occur. EHS will request prior radiation dose histories from all past employers.
  2. Dosimeters will be exchanged on a monthly or quarterly basis depending on the anticipated exposure level as evaluated by the EHS.
  3. All personnel occupational radiation dose records shall be maintained by EHS.
  4. It shall be the responsibility of each individual dosimeter recipient to wear and use the dosimeter (s) properly.
  5. Authorized Users are responsible for assuring their radiation workers are wearing badges appropriately and that badges are returned on time for reading.

NOTE: Departments may be charged for late or lost dosimeter.

The Radiation Safety Office may require the use of pocket dosimeters, ring dosimeter, or other monitoring devices when particular procedures are in operation.
Measured personnel occupational radiation doses, including bioassay results, are to be recorded and maintained on file by EHS.
The whole body dosimeter (or other device) is to be worn on the body where it will most likely approximate the radiation exposure to the head and torso of the wearer. A dosimeter assigned for whole body monitoring is not to be used to monitor the extremities (hands, forearms, feet, ankles). Separate badges must be assigned for extremity monitoring.

Generally, whole body dosimeters are to be worn between the waist and the neck. When a protective apron is worn, the badge is to be worn at the collar, outside the apron. In some circumstances, where exposure of the neck and lenses of the eyes is negligible, the monitoring badge may appropriately be worn under the apron. The Radiation Safety Office should be consulted for advice in these circumstances.

Extremity monitoring dosimeters (rings) are available in large or small size and for the right or left hand. Ring dosimeters should be worn whenever working with applicable sources. When using radioactive materials, the ring monitor element (label area) should be turned toward the palm. Gloves should be worn over the ring badge when contamination is possible.

The exposure of a personnel monitoring device to deceptively indicate a dose delivered to an individual is prohibited by North Carolina regulations.

Occupational radiation dose reports are sent to each radiation employee group representative. The report(s) must be posted or otherwise provided such that each group member may learn of his/her own dose record. Routine monitoring periods are currently monthly or quarterly. Each report will include the name, monitoring period date, dose (millirems) for the immediate past period, current calendar quarter, calendar year and the lifetime dose for each member of the group.
The UNC-CH fetal dose policy incorporates safety information and radiation dose guidelines for ensuring safe radiation limits for the conceptus of occupationally exposed employees. A copy of the complete policy, declaration form and information booklet is available through any Authorized User. The information must be maintained in the laboratory Radiation Safety records and be readily available to any interested individual. For occupationally exposed employees not working for specific Authorized Users, the policy and supporting information is available upon request from EHS. Any person is welcome to discuss the policy or obtain a copy, by contacting the EHS, Radiation Safety Office, 1120 Estes Drive Extension, CB #1650, 962-5507.

Internal Exposure

Bioassay is the determination of the kind, quantity or concentration, and location of radioactive material in the human body by direct (in vivo) measurement or by analysis (in vitro) of materials excreted from the body. Commonly employed bioassay techniques include urinalysis and thyroid monitoring. A bioassay program provides the necessary personnel monitoring to measure operational or accidental uptakes by radiation workers.

Radioactive material usage is approved only when the associated safety program, equipment, facilities and staff experience assures that safe use will be routinely maintained. The potential for radiation exposure due to inadvertent failures of procedures and equipment may increase, however, when certain combinations of radionuclides, chemical or physical forms and activities are involved.

Current health physics practices and safety survey results provide evidence that few, if any, radioactive material procedures currently in use allow routes for personnel uptakes. Some procedures do incorporate radionuclide form and activity combinations which warrant bioassay monitoring to assure that designated precautions remain effective.

A determination of bioassay personnel monitoring needs and frequency is made by the Radiation Safety Office during the review of applications. The status of existing usage programs is periodically reviewed through radiation worker registrations, surveys, inventory records and a semiannual or annual verification of radiation staff and radionuclide use limits.

Routine bioassay monitoring will be conducted when any individual is working with radionuclide form/activity combinations exceeding established limits. “Working with” includes withdrawing an aliquot from a stock supply which itself exceeds a limit, although the activity actually used is below the bioassay limit.

Tritium (H-3)

Urinalysis is required within 24 hours, if possible, but not later than 72 hours after working with 100 millicuries or more of tritium in any form.

Iodine (I-125, I-131)

An external thyroid bioassay by external counting is required within 24 hours, if possible, but not later than 72 hours after working with the following limits or greater:

  1. Processes in open room or bench with possible escape of iodine from process vessels:
    • 1 mCi if volatile form
    • 10 mCi if bound to nonvolatile agent
  2. Processes with possible escape of iodine carried out within a fume hood of adequate design, face velocity, and performance reliability:
    • 10 mCi if volatile form
    • 100 mCi if bound to nonvolatile agent
  3. Processes carried out within gloveboxes, ordinarily closed, but with possible release of iodine from process and occasional exposure to contaminated box and box leakage:
    • 100 mCi if volatile form
    • 1000 mCi if bound to nonvolatile agent

Other Radionuclides (C-14, P-32, S-35, Ca-45, Cr-51, etc.)

Urinalysis is required within 24 hours, if possible, but not later than 72 hours following potential ingestion, inhalation, or skin contamination of personnel. Additional urinalysis or external organ counting may be conducted, depending on the biological attributes of a specific radionuclide.

Any employee’s request for a bioassay analysis will be honored. Pregnant radiation workers using radioactive materials will be placed on a mandatory monthly bioassay schedule.

Standard methods for bioassay evaluations are normally sufficient to measure body or organ uptakes of radionuclides to a small fraction of an Annual Limit on Intake (ALI) . An outside laboratory specializing in bioassay services will be used for any analysis requiring extraordinary equipment or procedures. Internal dose results will be recorded, added to any external occupational dose, and maintained as part of the radiation worker’s overall personnel monitoring history.

Specific procedures for responding to any occupational radiation dose, which exceeds Level I or Level II in the following table, have been established.

Part of Body Investigation Level I
(millirems per monitoring period)
Investigation Level II
(millirems per monitoring period)
Whole body, head trunk, gonads or lens of the eyes 100 400
Extremities: arm, elbow, forearm, hand, thigh, knee, leg, foot 1000 3000
Skin 1000 3000
Conceptus 30 40

Action Procedures

When Level I doses are exceeded, the RSO shall send a written description of the dose report statistics, including the dose history for the previous two monitoring periods, to the person involved with a copy to the Authorized User. The individual will be requested to review his or her radiation safety procedures and work habits in an effort to maintain all doses as low as reasonably achievable. Radiation safety reviews and consultation are offered.

When Level II doses are exceeded, the RSO shall conduct a direct investigation of the situation, including an interview with the person involved. A written investigation report shall be made, including dose trends over the past one year (as available) for that person. The person involved is provided with a copy of the report for review and signature. Conclusions drawn from the investigation provide a basis for confirming or modifying the dose and for establishing corrective actions to be taken.

If a regulatory overexposure occurs, the required reports will be filed with the North Carolina Radiation Protection Section.

Part of Body Investigation Level I
(millirems per monitoring period)
Investigation Level II
(millirems per monitoring period)
Whole body* 100 400
Individual organ** 1000 3000

* Committed Effective Dose Equivalent (CEDE)
** Effective Dose Equivalent

Action Procedures

When a Level I dose is exceeded, the RSO will send a written description of the dose report, including the occupational dose history for the previous two monitoring periods, as available, to the person involved and to the Authorized User. The individual will be requested to review his or her radiation safety procedures and work habits in an effort to maintain all doses as low as reasonably achievable. Radiation safety reviews and consultations will be considered.

When a Level II dose is exceeded, the RSO will conduct a direct investigation of the situation, including an interview with the person involved. A written investigation report will be made, including total dose trends over the past 12 months (as available) for that person. The person involved will be provided with a copy of the report for review and signature. Conclusions drawn from the investigation will be used as a basis for confirming or modifying the dose value and for establishing any corrective actions to be taken.

Any confirmed internal dose of 10 millirems or more will be recorded in the involved individual’s permanent occupational radiation personnel dose record. When the individual is also being monitored for external occupational radiation dose, the internal dose and external Deep Dose Equivalent will be summed and recorded on the permanent external dose record as the Total Effective Dose Equivalent.

Whenever any regulatory radiation overexposure occurs, the required reports will be filed with the North Carolina Radiation Protection Section by the RSO.

Return to Chapter 7:
Emergencies
Proceed to Chapter 9:
Disposal of Radioactive Wastes