55 Radioactive Materials Safety Manual 125I IODINE-125 Half - Life Physical Biological Effective 60.1 days 138 days 41.9 days Radiaiton Emitted Type Energy (max) Gamma 35 keV (7%) X-rays 27-32 keV (138%) Conversion and Auger Electrons 3.2-35 keV (156-0.7%) External Hazard 1 meter 1 cm Dose rate from a 1 mCi (37 MBq) point source: 0.14 mrad/hr (1.4 µGy/hr) 1.4 rad/hr (14 mGy/hr) Internal Hazard Effective Committed Dose Ingestion Inhalation Equivalent per Unit Intake: 1.27 rem/µCi (3.44 x 10-7 Sv/Bq) 0.8 rem/µCi (2.16 x 10-7 Sv/Bq) Annual Limit on Intake: (ALI)* 40 µCi 60 µCi *ALIs expressed are from Appendix B, Table 1 – Iowa Administrative Code 641.40 (136C). Special Considerations • Volatilization of iodine from NaI solutions and from solutions of certain labeled compounds is a major concern. • Gaseous iodine is always present above solutions of NaI in proportion to the pH and temperature of the solution (the amount of gaseous iodine increases as the pH decreases below 9 and as the temperature falls to the freezing point of the solution). • Internal radiation dose from radioiodine may result from inhalation, ingestion, or absorption through the skin. • Seventy-five percent of the soluble radioiodine inhaled will be taken up by the body and thirty percent of this activity will accumulate in the thyroid. • High external doses to the fingers can result from direct handling of unshielded vials of millicurie quantity 125I solutions. Radiation Safety Practices • Special – EH&S provides onsite monitoring of all radioiodinations. This includes monitoring the set-up of a charcoal filtered glove box within the laboratory‘s fume hood and a “double glove tape up“ procedure for the researcher.
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