I-125 Standard Operating Procedures (Version: May 1997)

Introduction

Iodine-125 is a commonly used radionuclide with a half-life of 60 days, emitting gamma rays with a maximum energy of 0.035 MeV (Million Electron Volts). See Appendix A for the decay rate information for I-125.

Concerns

The major concern with using I-125 is radiation exposure in air over an unshielded vial. The dose rate at the opening of an unshielded vial containing 1 millicurie of I-125 can be 1,400 millirems per hour.

  • One millicurie = 2.22 x 109 dpm (disintegrations per minute)
  • This means that the quarterly SUNY As Low As Reasonably Achievable (ALARA) limit of 1875 millirem for the hands would be reached in 80 minutes.
  • The quarterly ALARA limit of 125 millirem for the whole body (assume 3 feet from the vial) would be reached in 5 minutes.

Shielding

Lead foil is the best shield for gamma rays from I-125. The half value layer for I-125 gamma rays in Lead is 0.02 mm., i.e. every 0.02 mm. of Lead reduces the I-125 gamma ray beam by 50%.

Detection

A small drop of contamination containing I-125 can be easily detected using a survey meter with a Sodium Iodide (NaI) Detector; it is also detectable with an end window Geiger-Mueller (GM) tube, but it is almost undetectable with a side window GM tube.

Equipment / Supplies

The following equipment and supplies must be available:

  • Portable radiation detector with a Sodium Iodide crystal.
  • Lead foil for shielding.
  • Disposable latex or plastic gloves.
  • Film badge.
  • Full-length lab coat.
  • Radioactive waste receptacle.
  • Pipettes dedicated to your use of I-125.
  • Commercial decontaminate, i.e. DuPont's "Count Off".
  • Absorbent bench covering or tray.

Safety Rules

If the following safety precautions are used, personnel radiation exposure will be as low as reasonably achievable (ALARA).

  1. Designate a specific area of the lab for I-125 handling.
  2. Place the 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 lab.
  3. All persons handling I-125 must wear a whole body badge.
  4. Full-length lab coats must be worn by all persons who handle I-125.
  5. Protect your hands from becoming contaminated from spills by wearing two pairs of disposable gloves.
  6. A detector must be in operation during the experiment, and preferably at all other times. To avoid contaminating the detector, place a thin sheet of plastic (i.e., Saran Wrap) around the detector.
  7. Place all vials and test tubes containing I-125 behind a Lead foil shield. Check the radiation level in front of the shield to determine if additional Lead foil should be added.
  8. Do not work directly over an open container of I-125.
  9. Never pipette I-125 or "any radionuclide" by mouth.
  10. Only use pipettes which have been dedicated to your specific use of I-125. Pipettes will easily become contaminated and therefore, should not be shared with others.
  11. Check your gloves frequently for contamination with a sodium iodide detector. If contamination is found, immediately dispose of the gloves in the radioactive waste container.

Post-Use Procedures

After handling I-125:

  • Use the Geiger Counter to check your hands, lab coat, shoes, clothing, centrifuges, water baths, work bench and floor.
  • If any contamination is found on your shoes and/or clothing, contact the RSO. You will likely have to remove the item temporarily until the radiation decays. The RSO has some disposable clothing that you can wear home. We do not have any disposable shoes.
  • If any contamination is found on your hands, wash thoroughly with soap and water. This will usually be sufficient to remove the surface contamination. If it does not, contact the RSO for assistance.
  • If any contamination is found on equipment, etc., use a commercial radiation contamination remover (i.e. Count Off) with paper towels to clean up the equipment.
  • Place the towels in the radioactive waste receptacle.
  • If contamination cannot be removed, contact the RSO to obtain shielding materials and place a "radiation" label on the equipment indicating that it is I-125, maximum cpm found, and the date you measured the level.
  • Inform your fellow lab workers if any unremovable contamination is found.
  • Check the normal trash container to make sure no radioactive waste has been accidentally placed there.
  • Store the waste temporarily in containers which are sufficient to absorb I-125's gamma rays.
  • Wash your hands thoroughly.
  • Bring the waste to the Radwaste Room frequently. We accept waste every Thursday or by arrangement in case of an emergency.

Any questions about these procedures?

Call the Radiation Safety Office: 464-6510


APPENDIX A
DECAY RATE OF I-125
Days Elapsed % of Activity Remaining Decay Factor
0 100.0 1.00
10 89.1 0.891
20 79.4 0.794
30 70.7 0.707
40 63.0 0.630
50 56.1 0.561
60 50.0 0.500
70 44.5 0.445
80 39.7 0.397
90 35.4 0.354
100 31.5 0.315
110 28.1 0.281
120 25.0 0.250
... ... ...
600 (10 half-lives) 0.1 0.001

For example, if your vial contained 500 microcuries of I-125 on 7/1/90, the amount of activity remaining on 7/11/90 (10 elapsed days) would be:

Activity x Decay Factor = 500 microcuries x 0.891 = 446 microcuries