Any individual who enters a Restricted Area under such circumstances that he receives, or is likely to receive a dose in any calendar year in excess of 10% of the applicable values specified in Title-A Radioactive Materials Regulation 61-63, RHA 3.17 and listed below will be monitored for occupational external radiation exposure. Personnel monitoring will be by TLD (thermoluminescent dosimeter) provided by a NAVLAP certified vendor.
A. Personnel TLDs
All personnel TLDs will be changed quarterly.
The following practices will be observed when wearing a personnel monitoring device:
Self-reading dosimeters are fountain pen sized devices that directly measure exposure to X or gamma radiation. A separate charging device is used to set the device to the zero position. Like charges are placed on a center electrode and a movable quartz fiber. As radiation is incident on the sensitive volume of the dosimeter the charge between the fixed and movable electrode is lost and the movable quartz fiber moves closer to the fixed electrode. This movement may be viewed against an internal scale through a built in compound microscope. Self-reading dosimeters are available in various scales, the most prevalent being 0 - 200 millirem.
C. Internal Monitoring - Bioassays
Persons who may be exposed to radioactive materials in such a manner that an internal uptake approaching 0.1 ALI is possible shall submit urine samples for analysis.
1. Routine Measurements
a. Baseline measurements, An individual's baseline measurement of radioactive material within the body will be conducted prior to initial work activities that involve exposure to radiation or radioactive materials, for which monitoring is required
b. Periodic measurements. - The frequency of periodic measurements shall be based on the worker's access, work practices, measured levels of airborne radioactive material, and exposure time. Periodic measurements will be made when the cumulative exposure to airborne radioactivity, since the most recent bioassay measurement, is > 0.02 ALI (40 DAC hours).
c. Termination measurements. When an individual is no longer subject to the bioassay program, because of termination of employment or change in employment status.
2. Internal Uptake
A bioassay will also be initiated anytime an internal uptake of radioactive material is suspected to have occurred, for instance, when facial and/or nasal contamination is found.
3. Special Monitoring
Situations such as a failed respiratory protective device, inadequate engineering controls, inadvertent ingestion, contamination of a wound, or skin absorption shall be evaluated on a case‑by‑case basis. Circumstances that should be considered when determining whether potential uptakes should be evaluated include:
a. The presence of unusually high levels of facial and/or nasal contamination,
b. Entry into airborne radioactivity areas without appropriate exposure controls,
c. Operational events with a reasonable likelihood that a worker was exposed to unknown quantities of airborne radioactive material (e.g., loss of system or container integrity),
d. Known or suspected incidents of a worker ingesting radioactive material,
e. Incidents that result in contamination of wounds or other skin absorptions,
f. Evidence of damage to or failure of a respiratory protective device.
4. Evaluation Level
If initial bioassay measurements indicate that an intake is greater than an evaluation level of 0.02 ALI, additional available data, such as airborne measurements or additional bioassay measurements, will be used to obtain the best estimate of actual intake
5. Investigation Level
For single intakes that are greater than 10% of the ALI, a thorough investigation of the exposure shall be made. If an internal uptake exceeds an investigation level of 0.1 ALI, multiple bioassay measurements and an evaluation of available workplace monitoring data will be conducted. In this case, daily measurements will be made until a pattern of bodily retention and excretion can be established.
a. For uptakes exceeding the ALI’s, the bioassay data evaluations shall consider additional data on the physical and chemical characteristics and the exposed individual's physical and biokinetic processes.
Bioassays will be performed by obtaining a urine sample from the exposed individual, mixing one ml. of the sample urine with 10 ml. of a commercially available scintillation cocktail, and analyzing the sample with a liquid scintillation counter.
7. Thyroid Scan
Bioassay for I-125 may also be conducted by performing a thyroid count. This analysis will be preformed utilizing a NaI(TL) crystal detector, designed for the detection of low energy (10-60 keV.)gamma photons. The detector will be placed in contact with the neck, over the thyroid of the individual under consideration, and conducting a 10 minute count.a. The instrument used to conduct the thyroid count will have the efficiency set utilizing an I-129 NIST traceable source placed within a plastic neck phantom which approximates the physical characteristics and geometry of the thyroid of reference man.