60.14 Days



Beta Energy

35.5 keV

Travel distance

  • Air: 443 feet or 135m (99% reduction)
  • Plexiglass/Lucite: 0.5 mm (99% reduction)

Annual Intake Limit

  • Inhalation: 60 µCi
  • Ingestion: 40 µCi


  • Portable Survey Meters:
    • Geiger-Mueller with NaI scintillation probe
  • Wipe Test: LSC for removable contamination


  • Use 3 mm thick lead for µCi quantities

Dosimeter Monitoring

  • Always wear radiation dosimetry monitoring badges [body & ring] when handling > 1 mCi of 125I in a procedure
  • Conduct a baseline thyroid scan prior to first use of 1 mCi or more of radioactive iodine
  • Conduct thyroid scan no earlier than 24 hours but within 1 week of handling 1 mCi or more of 125I or after any suspected intake


  • Avoid skin absorption, ingestion, inhalation & injection
  • Use shielding [lead or leaded Plexiglas] to minimize exposure while handling mCi quantities of 125I
  • Avoid making low pH [acidic] solutions containing 125I to avoid volatilization
  • For Iodinations:
    • Use a cannula adapter needle to vent stock vials of 125I used; this prevents puff releases
    • Cover test tubes used to count or separate fractions from iodinations with parafilm or other tight caps to prevent release while counting or moving outside the fume hood


  • Minimize the number of times the primary container is opened and immediately reseal after each use. If used repeatedly, aliquot the required amounts into separate storage vials.
  • Na 125I can penetrate through gloves – wear two pairs and change the outer pair after every step in the iodination procedure
    • Frequently monitor your hands

Radiological Data

  • Radiotoxicity:
    • 3.44E-7 Sv/Bq (1273 mrem/uCi) of 125I ingested [Thyroid];
    • 2.16 E-7 Sv/Bq (799 mrem/uCi) of 125I inhaled [Thyroid]
  • Critical Organ:
    • Thyroid Gland
  • Intake Routes:
    • Ingestion, inhalation, injection, absorption
  • Radiological Hazard:
    • External & Internal exposure; Contamination