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Radiation Safety Training Module
Refresher Training
ISU Technical Safety Office
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Pocatello, ID 83209
(208) 282-2311
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Bioassay
 
A bioassay involves directly measuring the radioactive material that may be present in an individual’s body. In some instance, bioassays mean the radioactive materials excreted from the body to infer what is present within human tissue. 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 from unconfined, dispersible radioactive material and as authorized by the RSO. 
 
(right: thyroid counter)
Definitions:
ALI - The Annual Limit on Intake is the quantity of any radionuclide, which if taken into the body by inhalation or ingestion in a year, produces a committed effective dose equivalent of 5 rem.  Because of differences in physiological transport mechanisms, the ALIs vary depending on the route of intake.  For purposes of contamination control and bioassay procedures, the most conservative ALI, be it for either inhalation or ingestion is employed.

Bioassay interval - The bioassay interval is the maximum time that may elapse between bioassays that will assure detection of the verification level for a given nuclide and assay method.  The bioassay interval for a particular radionuclide is determined by its physical and metabolic characteristics, and by the instrumentation used for the measurement.  For most commonly used radionuclides and typical analytical systems, the bioassay interval is 13 weeks (one calendar quarter); for P-32, and a few other very short-lived radionuclides, however, the bioassay interval is only one month.

Minimally exposed: 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 exposed to contamination exceeding the levels specified under "Conditions Requiring Bioassays", however, a non-routine bioassay will be required.

Potentially exposed: 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.

Conditions requiring bioassays:
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.  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. 
  Key Words: ALI, minimally exposed, potentially internal exposed
 
Page: 10 of: 12
  Quiz: How do you know if you are required to perform a bioassay?
 
a) Refer to ALI, DAC, and dose conversions book. b) TSO tells you to do it. c) You have had to do them before. d) I don't know.
  Appendix B to 10 CFR 20 - ALIs, DACs etc.
  P-32 Ingestion Reports on NMSS Newsletter
   

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