Isotope Information
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: 4x101 µCi Thyroid ingestion 1x102 µCi
- Inhalation: 6x101 µCi Thyroid inhalation 2x102 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 sample vials of iodinated compounds,
should always be opened in a fume hood. Personnel using I-125 in hundreds of microcuries
or more must wear double gloves and should change gloves as soon as the gloves become
contaminated. Thyroid count bioassays must be performed following an iodination.
Waste Disposal: Call radiation safety office.
Hydrogen -3
Physical Characteristics:
- Half-life: 12.3 years
- Emissions: Beta particles with a maximum energy of 18.6 keV and an average energy of 5.7 keV.
- Maximum Range in Air: 4.7 mm in air; 6 mm in tissue.
- Fraction trans