Radionuclide Safety Guideline for I-125

Physical Data

  • Gamma - 35.5 keV (7% abundance)
  • X-ray - 27 keV (113% abundance)

Half-Life

  • Physical: 60.14 days
  • Biological: 120 - 138 days (unbound iodine)
  • Effective: 42 days (unbound iodine)

Range 

  • Theoretically infinite in air (unshielded)

External Hazard

  • Is an external exposure hazard. Unshielded exposure rate from a 1 mCi point source at a distance of 1 cm is 1,400 mrem/hour.

Internal Hazard

  • Critical Organ: Thyroid Gland. Internal uptake results in whole body and thyroid exposure.

Skin & Eye Hazard

  • Is an external exposure hazard. Unshielded exposure rate from a 1 mCi point source at a distance of 1 cm is 1,400 mrem/hour.

Safety Guidelines

  • Whole body and ring dosimeters are required to be worn by individuals "routinely working with > 5 mCi quantities of I-125."
  • Wear a lab coat and disposable gloves when working with I-125. Change gloves frequently.
  • Avoid direct eye contact - wear safety glasses to avoid splashing I-125 into eyes.
  • Store I-125 source vials and solutions behind lead shields.
  • Internal radiation doses from radioiodine may result from inhalation, ingestion or absorption through the skin.
  • Unbound sodium iodide (NaI) and certain labeled compounds can readily volatilize.
  • All work with unbound compounds must be conducted within a properly working fume hood in an EH-approved mini-hood with a charcoal filter. Replace the filter as necessary. For more information contact Laurie Scholl at 353-5389.
  • Use remote handling tools to manipulate mCi quantities of I-125.
  • Neutralize spills of unbound NaI with sodium thiosulfate solution.
  • A baseline thyroid bioassay is required prior to using 100 uCi or more of unbound (NaI) I-125.
  • Post-iodination thyroid bioassays are required within 24-72 hours. Contact EHS at 335-8501 to schedule a thyroid count. 

updated 01/2013