Science Gateway
Calcium - 45
Carbon - 14
Chromium - 51
Hydrogen - 3
Iodine - 125
Iron - 59
Manganese - 54
Phosphorus - 32
Phosphorus - 33
Sodium - 22
Sulfur - 35

IODINE - 125


Physical Half-life: 60.14 days
Radiations:x/gamma 35 keV
External Exposure:External hazard when mCi quantities are present. Radiation exposures from 1.0 mCi source are 62.4 mR/hr and 0.156 mR/hr at 5 cm & 100 cm, respectively.
Biological Data: ALI 0.04 mCi (ingestion), 0.06 mCi (inhalation), thyroid
Biological half-life 138 days
Effective half-life 42 days
Critical Organs Thyroid
Bioassay Thyroid Scans
Shielding: HVL 0.017 mm of lead; TVL 0.056 mm of lead
& Efficiency
LSC (Eff. ~50%)
Gamma Counter (Eff. 50-90%)
Low Energy Gamma (Scintillation) Meter (Eff. 50-90%)

Special Considerations

  • Work with volatile 125Fe (e.g. NaI) must be done in an approved fume hood.
  • Use a breathing zone monitor when working with 1.0 mCi or more of volatile radioiodine or 10.0 mCi or more of nonvolatile radioiodine.
  • Survey the work area immediately following any iodination. Document survey results. Send a copy of the survey results to the Radiation Safety Officer if 50 mCi or more are used.
  • Thyroid bioassay is required ater using greater than or equal to 100 uCi of volatile 125I or greater than or equal to 1.0 mCi of 125 bound to a nonvolatile compound. Bioassay must be done within 10 days after receipt of the iodine.
  • To minimize volatilization avoid acidic solutions. Do not store NaI solutions in freezers. Seal waste containers on the completion of our iodination.
  • Wear a radiation badge when handling 1.0 mCi or more of 125I.
  • Do not use GM survey meters to monitor for contamination as they are not sensitive to contamination levels of concern.