Part 500: Personnel Monitoring

• 500.10 Introduction
• 500.20 Determining If Personnel Monitoring Is Required
• 500.30 Obtaining Personal Dosimeters
• 500.40 Use of Dosimeters
• 500.50 Use of Other Monitoring Devices
• 500.60 Allowable Occupational Radiation Doses
• 500.70 Dosimetry Results
• 500.80 Bioassay Requirements

500.10 Introduction

Personnel monitoring, or dosimetry, is an important safety practice when using radioactive material or working with radiation-producing equipment. Thermoluminescent dosimeters (TLDs) are the primary method of detection used for monitoring doses received from radiation. These can be obtained from commercial vendors as badges to measure whole-body doses or as rings to measure extremity doses. Bioassays may also be performed to monitor any internal exposure to radioactive materials. All exposure measurements are expressed in units of mrem (millirems).

500.20 Determining If Personnel Monitoring Is Required:

1. Thermoluminescent dosimeters are not capable of detecting all types of radiation. Radiation that does not have sufficient energy to penetrate the dosimeter will not be recorded. For this reason, personnel monitoring is not required in all cases. The following lists the types of radiation and whether or not monitoring is required (also, refer to Part 900):
   • Alpha emitters: No Monitoring Required
   • Beta emitters, where E_max is less than 200 keV: No Monitoring Required
   • Beta emitters, where E_max is equal to or greater than 200 keV: Monitoring Required
   • Gamma emitters: Monitoring Required
   • X-ray emitters, from radioactive sources or X-ray equipment: Monitoring Required
   • Neutron emitters: Monitoring Required
2. All personnel who may potentially be exposed to radiation requiring personnel monitoring must be supplied with a personal dosimeter.

500.30 Obtaining Personal Dosimeters

1. The authorized user can order a TLD badge or ring by submitting a written request to the radiation safety officer or designee. The following information is needed for each individual for whom a TLD is requested:
1. Name
2. Social Security Number
3. Date of Birth
4. Gender
2. TLDs are supplied to the university on a monthly or quarterly basis by a commercial vendor. The badges and rings are usually assembled and labeled by the vendor during the middle of the month and mailed to the university a week prior to the first of the month. Any changes in personnel monitoring should be made before the vendor mails the TLD badges. Once a TLD badge or ring is sent, it is considered used and the authorized user will be charged for the TLD badge whether or not it is actually used. In most cases, new badges or rings can usually be obtained in five working days.
3. The cost for personnel monitoring will be charged back to the authorized user. The authorized user will be charged replacement fee for lost badges or rings. Contact the radiation safety officer or designee for current prices of personnel monitoring services.
4. When an individual no longer requires a personal dosimeter because he/she is not using radioactive material or radiation-producing equipment or has left the university, it is the responsibility of the authorized user to notify the radiation safety officer and cancel the personal dosimeter.

500.40 Use of Dosimeters

1. Personal dosimeters are assigned to one individual and are not to be used by any other individual during the monitoring period. Authorized users are responsible for ensuring dosimeters are used by the appropriate individual and are worn properly.
2. Control badges are used to determine the background radiation levels for each user group. This radiation dose is subtracted from the individual TLD badge to determine the occupational dose received. It is essential that the control badge be stored in an appropriate location and not be exposed to any source of radiation.
3. User groups having frequent personnel changes are allowed to request spare TLD badges. The spare TLD badges can be used for individuals needing monitoring for a short time only (i.e., less than a month) or until a permanent TLD badge can be obtained. The authorized user must submit a monthly written report to the radiation safety officer documenting the individual who used the spare badge, their social security number and date of birth, or that the spare badge was not used. Once a spare badge has been used by one individual, it may not be used by any other individual during the monitoring period.

500.50 Use of Other Monitoring Devices

In special situations, the Radiation Safety Committee may allow or require pocket ionization chambers to be used. Although not as accurate or as sensitive as TLD monitoring, they provide immediate information on radiation exposures.

1. For single exposures of large groups of individuals (e.g., lecture demonstrations, orientation tours), monitors may be worn by a few representative individuals only, provided the total dose of any one individual is not expected to exceed five millirems during the event.
2. It shall be the responsibility of the authorized user to read the pocket ionization chambers and to provide the radiation safety officer with a written record of the individuals monitored and the doses received.

500.60 Allowable Occupational Radiation Doses

1. The following are the maximum radiation doses individuals are allowed to receive per year when working with radioactive materials or radiation-producing equipment:
   
   Allowable Occupational Dose Limits (in rems)
   
   Per Year
   Whole body (head and trunk, 5 active blood-forming organs, or gonads)
   Lens of the eyes 15
   Skin and extremities (hands, 50 forearms, feet, and ankles)
2. Minors - The allowed occupational dose limits for minors (less than eighteen years old) are ten percent of the above occupational dose limits.
3. Protection of an Embryo/Fetus:
1. Nuclear Regulatory Commission regulations require that the occupational dose to an embryo/fetus during the entire pregnancy not exceed 0.5 rem. This dose limit only applies to a female who voluntarily informs her employer (i.e., informs the authorized user and the radiation safety officer) that she is pregnant and the estimated date of conception, or intends to become pregnant. Such an employee is then "declared pregnant" and is entitled to additional safety precautions during the term of pregnancy.
2. Additional information or consultation on prenatal radiation exposure and safety precautions is available from the radiation safety officer. Any such requests will be held strictly confidential.
4. It is a requirement that the amount of radiation received by an individual be kept as low as possible. Any situation where an individual receives a whole body dose of more than fifty millirems of penetrating radiation per month or per quarter, depending on the monitoring period, will be investigated by the radiation safety officer to determine why this dose was received and what steps can be taken to minimize radiation doses.

500.70 Dosimetry Results

The authorized user will be sent the dosimetry results of the previous monitoring period. The authorized user is responsible for ensuring each individual being monitored is notified of their dosimetry results. The dosimetry results should be treated as confidential and the authorized user should allow each monitored individual to know only their results.

500.80 Bioassay Requirements

Bioassays aid in determining the extent of an individual's dose received from internally deposited radioactive materials. Bioassays are required when individuals use tritium or iodine radioisotopes at specified quantities and/or within certain time periods. It is the authorized user's responsibility to indicate in the application to use radioactive materials whether or not bioassays will be required for the type of activities being conducted. Individuals using tritium or iodine radioisotopes under conditions described below are required to participate in the bioassay program.

The radiation safety officer will maintain the procedures and equipment for conducting the necessary bioassays.

1. Tritium (³H)
1. A tritium bioassay is required whenever an individual uses unsealed tritium isotopes in single or cumulative quantities greater than 100 millicuries within a one month period.
2. Type of bioassay - Analysis of urine sample.
3. Prior to working with tritium in the above specified amounts, the individual must obtain a bioassay to establish a baseline level of tritium within the body.
4. All bioassay samples should not be collected until at least two hours after termination of the potential exposure to allow for equilibration of tritium within the body.
5. The first routine bioassay sample should be taken within twenty-four hours after termination of the potential exposure, if possible, but not later than seventy-two hours.
6. Succeeding routine bioassay samples must be collected at two week intervals as long as the individual continues to work with tritium in the amounts specified above.
7. The urinary tritium sample concentration that will trigger corrective action is five µCi per liter.
8. A tritium bioassay may also be required because of an accidental exposure to tritium (e.g., laboratory accident, skin contact, ingestion, inhalation, etc.).
2. Radioactive Iodine (¹²⁵I)
1. A radioactive iodine bioassay is required whenever an individual uses unsealed iodine isotopes in single or cumulative quantities greater than one millicurie within a three month period.
2. Type of bioassay - External monitoring of the thyroid.
3. Prior to working with iodine isotopes in the above specified amounts, the individual must obtain a bioassay to establish a baseline level of radioactive iodine within the body.
4. All bioassays should not be performed until at least six hours after termination of the potential exposure to allow for accumulation of iodine in the thyroid.
5. The first routine bioassay must be taken within seventy-two hours after termination of the potential exposure.
6. Succeeding routine bioassays must be taken at two weeks intervals as long as the individual continues to work with radioactive iodine in the amounts specified above.
7. All users handling radioactive iodine or who are sufficiently close to the actual use must participate in the bioassay program.
8. The thyroid radioactive iodine-125 concentration that will trigger corrective action is 0.12 µCi.
9. A bioassay may also be required because of an accidental exposure to radioactive iodine (e.g., laboratory accident, skin contact, ingestion, inhalation, etc.).