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Radiation Safety Training Module
Radiation Safety Training
Study Guide
ISU Technical Safety Office, Campus Box 8106
Pocatello, ID 83209
(208) 282-2311/2310

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Monitoring of
internal exposure 

Internal exposures - Bioassay
Bioassay measurements used for demonstrating the compliance with the occupational dose limits should be conducted often enough to identify any quantify potential exposure, during any year, are likely to collectively exceed 0.1 times the ALI (Reg. Guide 8.9, 10CFR 20).
 
A bioassay is required whenever personal contamination or injury caused by a contaminated object occurs, or if airborne radioactivity may have been inhaled.  Routine bioassays, at intervals determined by the radionuclides used, are required from each user who handles more than certain threshold quantities of dispersible radioactive materials.  A routine bioassay may be waived when ap­propriate surveys for contamination, conducted during and after each use of radioactive material according to recommended procedures, demonstrate that there was essentially no exposure to unconfined, dispersible radioactive material and as authorized by the RSO.
 
A radiation user who handles a cumulative quantity of radioactive materials in dispersible form of less than 1 ALI per month, averaged over the bioassay interval, is unlikely to experience an annual intake of 0.1 ALI and does not require routine bioassays.  If a worker is exposed to contamination exceeding the levels specified under "Conditions Requiring Bioassays", however, a non-routine bioassay will be required.
 
At ISU, a radiation user who handles a cumulative quantity of radioactive materials in dispersible form of more than 1 ALI per month, averaged over the bioassay interval, is considered to be potentially exposed to an annual intake of more than 0.1 ALI. Such an individual must perform or obtain bioassays routinely unless the records of contamination surveys of both the user and the RSO verify that there was no exposure to unconfined radioactive materials exceeding the levels specified.
 
Individuals who handle dispersible radioiodine compounds may be required to obtain in vivo measurements of radioiodine in the thyroid, performed by the RSO, at specified intervals.  Individuals who handle other radionuclides in dispersible forms may be required to perform assays of radioactivity in urine on a routine basis to document the absence of radioactivity in the body or to determine the magnitude of any exposure.  Other types of assays may be utilized if, in the judgment of the RSO, such assays will meet the intent of this policy more effectively.
Conditions requiring bioassay:

The optimum time for performing a bioassay is within a few days after a potential exposure, and therefore
each user will perform a screening assay within a few days after handling any unusually large quantities, or after performing any procedure involving a greater than usual opportunity for exposure. Subsequent routine bioassays would not be required again until the end of another full bioassay interval unless another unusual exposure situation occurred. 

  Thyroid Counter

The Technical Safety Office will notify users when a bioassay is due (upon delivery of the radioactive material), i.e. the expiration of the bioassay interval, but it is the responsibility of the user to complete the bioassay promptly.
  • A bioassay is required within 5 days for each individual having contamination of the skin or hair exceeding 10 RCL.
  • A bioassay is required within the normal bioassay interval for any individual having skin or hair contamination exceeding 1 RCL.
  • A bioassay is required within 5 days for each individual involved in a spill, or other uncontrolled release, of >0.5 ALI of radioactive material outside of a properly functioning fume hood or >5 ALI inside a hood.
  • A bioassay is required within 5 days for each individual who was present in an area during a time when removable contamination exceeding 100 RCL was present on any readily accessible surface.
  • A bioassay is required within the normal bioassay interval for each individual who was present in an area during a time when removable contamination exceeding 10 RCL was present on any readily accessible surface.
  • A bioassay is required within the normal bioassay interval for personnel who work in laboratories that have >1 ALI of cumulative quantity handled, averaged over the bioassay intervals. The determination of the cumulative quantity handled will be based primarily on records of receipts and disposals of radioactive materials, with adjustments for individual work assignments as defined by the responsible user. Routine bioassays may be waived at the discretion of the RSO if the records of contamination surveys of both the user and the RSO verify that there was no exposure to unconfined radioactive materials exceeding the levels specified above and no incidents of personal contamination since the last bioassay. When mixtures of radionuclides are present in the laboratory, the necessity of a bioassay will be based upon a sum of the fractions evaluation. 
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