Iodine-125

Physical Characteristics:

• Half-life: 60.1 days
• Emissions: Principal emissions are a 35 keV gamma ray and 27 – 32 keV x-rays.
• Half-Value Layer: 0.02 mm lead; 2 cm in tissue.
• The half-value layer is the amount of material required to reduce the radiation intensity by 50%.

Dose:

• Dose rate at 10 cm: 15 mrem/hour/mCi (for an unshielded point source)

Shielding:

• Lead foil for shielding I-125 gamma rays
• Half value layer for I-125 gamma ray is 0.02mm (i.e. every 0.02 mm. of Lead reduces the I-125 gamma ray beam by 50% )

Annual Intake Limits (ALI)

• Ingestion: 4×101 µCi Thyroid ingestion 1×102 µCi
• Inhalation: 6×101 µCi Thyroid inhalation 2×102 µCi

Note: 1.0ALI = 5,000 mrem CEDE

Detection:

• A survey meter equipped with a G-M pancake or thin-window probe is not recommended for detecting I-125. Typical efficiency for a G-M pancake is <1%.
• A survey meter equipped with a thin crystal NaI scintillation probe is best for detection of the I-125 gamma. Typical efficiency is 29%-33%.
• Either a gamma counter or a liquid scintillation counter can be used to detect removable I-125 contamination on wipe tests smears. Both have efficiencies for detecting I-125 of about 70%.
• Whole Body dosimeter: Required
• Finger dosimeter: Required.

Precautions:
Volatile iodine can be released from iodinated compounds containing hundreds of microcuries or more of I-125. Containers of I-125, including samp