56 Radioactive Materials Safety Manual Environmental Health and Safety • Dosimetry – Whole-body dosimeter required when working with quantities greater than 5 mCi (185 MBq). • Bioassay – Thyroid scan required within 24 to 96 hours for each individual performing a radioiodination or any individual who may have come in contact with volatile 125I compounds. • Shielding – 0.8 mm lead provides 95% attenuation. Lead HVL is 0.017mm. • Surveys – Scintillation meter surveys; wipes analyzed in an LSC or gamma counter. • General – All work with potentially volatile 125I labeled compounds must be conducted in a fume hood (quantities of 10 µCi or less of relatively stable compounds such as labeled proteins may be used safely on the open bench). ¤ NaI in NaOH solutions should not be acidified or frozen. ¤ Researchers working with volatile 125I compounds should double-glove, changing the outer pair of gloves frequently. ¤ Emergency procedures for potential releases of volatile radionuclides (found on page 26 and on the laboratory wall chart) should be reviewed by the researcher before performing an iodination. ¤ Sodium thiosulfate solution should be utilized to stabilize any spilled 125I before decontamination procedures are initiated. ¤ Bare source vials of 125I should not be handled directly unless leaded rubber gloves are worn. ¤ Shielded containers, tongs, or vial/tube racks should be used for manipulating vials of millicurie quantity 125I.