1.    Data
2.    Monitoring
3.    Facilities
4.    Concerns
5.    Waste

Half-life (T1/2) = 60 days    
Maximum gamma energy = 35Kev 7% gamma  
  100 % electron capture  

Minimum range in air = N/A
Critical organ = Thyroid gland
Annual limits on intake (ALI) = 0.06 mCi via inhalation, 0.04 mCi via ingestion
Detection = meter with NaI Probe, Gamma Counter, LSC

  1. Monitoring
  2. 1.

    Personnel dosimeter badges will be issued to all personnel working in laboratories where I-125 is utilized. Also, TLD finger type extremity monitors will be issued to all personnel handling I-125. Wear the ring badge inside the disposable glove. However, RIA kit users do not require dosimeters and work can be done on the benchtop.


    Appropriate survey instrumentation will be required of all laboratories working with I-125. (i.e., A sodium iodide scintillation detector) G-M detectors are not likely to detect the presence of I-125 in amounts less than about 100,000 dpm (0.05 uCi). Survey instrumentation must be calibrated on an annual basis. Annual calibration is handled by the EHRS Department.


    After each use of I-125 in the laboratory, the work area must be surveyed with an appropriate survey instrument to detect any areas of contamination. Check your hands, shoes, clothing, work bench, floor, and laboratory equipment. These surveys need not be logged unless your laboratory is instructed to do so by the Radiation Safety Officer.

  3. Facilities
  4. 1.

    All I-125 should be stored and used behind lead foil. Lead foil is the best shield for gamma rays from I-125 when used in hundreds of microcuries or in millicurie quantities. No shielding is needed when used in low microcurie amounts such as for RIA kits. The half value layer for I-125 gamma rays in lead is .02 mm. (i.e., every .02 mm of lead reduces the I-125 gamma ray beam by 50%).


    Designate a specific area of the laboratory for I-125 handling. Place the lead shielding near a wall (not toward another work area on the other side of the bench) away from the main flow of traffic in the laboratory.


    Dry runs are recommended with all new uses or procedures regarding I-125 in order to preclude unexpected complications.

    4. The University license does not permit any iodinations.
  5. Concerns
  6.   1.

    The dose rate at the opening of an unshielded vial containing 1 millicurie of I-125 can be 1,400 millirems per hour.

    This means that the quarterly NRC/PaDEP limit of 18,250 millirems for the hands would be reached in 13 hours. The quarterly NRC/Pa DEP limit of 1,250 millirems for the whole body (assume 3 feet from the vial) would be reached in 7,440 hours.


    "Free I-125 (I2 or aqueous NaI) is easily absorbed through intact skin and can penetrate plastics.  "Free" forms are easily volatilized, especially in acid solutions and present a serious airborne hazard.   Containers of I-125, including sample vials of iodinated compounds, should always be opened in a fume hood. (See the section on Internal Monitoring)


    Never use bleach as a disinfectant, or use bleach to decontaminate a spill, as it can volatilize the iodine. (This is true for S-35 also.)  In addition, do not use hot water, acids or acidic detergents because volatile Iodine may also be produced. Use an iodine based disinfectant instead.

      4. Do not freeze I-125. Also, keep the pH of iodine materials basic in order to reduce volatility.

    Change gloves frequently, or monitor gloves frequently, during the use of I-125. Wash your hands thoroughly after using I-125. It is recommended to wear two pairs of disposable gloves when working with I-125.

  7. Waste

Store the waste temporarily in containers which are sufficient to absorb I-125's gamma rays. Call the McNeil Science & Technology Center or the Griffith Hall Stockroom when the waste is ready for a pick-up. (See Radioactive Waste Procedures)


Check and survey the normal trash container to make sure no radioactive waste has been accidentally placed there.

University of the Sciences in Philadelphia • 600 South Forty-third Street • Philadelphia, PA 19104-4495 • phone: 215-596-8800 • email: