THE USE OF I-125 IN THE LABORATORY

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

Half-life (T½) = 60 days
Maximum gamma energy = 35 KeV        7% gamma
                                                           100% electron capture
Critical organ = Thyroid gland.

1. Monitoring

	1.	Personnel dosimeter badges will be issued to all personnel working in laboratories where I-125 is utilized. TLD finger type extremity monitors will be issued to all personnel handling I-125.
	2.	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 (0.5 uCi). Survey instrumentation must be calibrated on an annual basis. Annual calibration is handled by the Safety Department.
	3.	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.

2. Facilities

	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%).
	2.	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.
	3.	Dry runs are recommended with all new uses or procedures regarding I-125 in order to preclude unexpected complications.
	4.	The University license, currently, does not permit any iodinations.

3. Concerns

	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 limit of 18,250 millirems for the hands would be reached in 13 hours. The quarterly NRC limit of 1,250 millirems for the whole body (assume 3 feet from the vial) would be reached in 7,440 hours.
	2.	"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)
	3.	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.
	4.	Change gloves frequently, or monitor gloves frequently, during the use of I-125. Wash your hands thoroughly after using I-125. Personnel/students working with hundreds of microcuries or more must wear double gloves.

4. Waste