Iodine 125

Half-life

60.14 Days

Emitter

Gamma

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

Detection

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

Shielding

• 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

Precautions

• 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

Recommendations

• 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