STANDARD OPERATING PROCEDURES
IODINE-125
version: September 26, 1991
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 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.
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
.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 with a survey meter with a Sodium Iodide (NaI) Detector.
EQUIPMENT / SUPPLIES
The following equipment and supplies must be available:
- portable radiation detector with a Sodium Iodide
crystal. (We recommend the Ludlum Model 3-98 or an equivalent)
- Lead foil for shielding.
Lead foil is available from many vendors and
the cost is very reasonable.
- Disposable latex or plastic gloves.
- Film badge and ring badge.
- Full-length lab coat.
- Radioactive waste receptacle.
- Pipettes dedicated to your use of I-125.
- Commercial decontaminate, i.e. DuPont's "Count Off".
SAFETY RULES
If the following safety precautions are used, personnel radiation
exposure will be as low as reasonably achievable.
- Designate a specific area of the lab for I-125 handling.
- 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.
- All persons in the laboratory must wear a whole body
film badge when in the lab, even those who are not
handling I-125.
- All persons handling I-125 must wear a ring badge on the
hand which is most frequently used to handle vials,
samples, pipettes, etc. containing I-125.
- Full-length lab coats must be worn by all persons who
handle I-125.
- Protect your hands from becoming contaminated from
spills by wearing two pairs of disposable gloves.
- 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
- 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.
- Do not work directly over an open container of I-125.
- Never pipette I-125 by mouth.
- 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.
- Check your gloves frequently for contamination with a
Geiger Counter.
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, 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, place a
"radiation" label on the equipment indicating that it
is I-125, maximum cpm found, and the date you measured
the level.
- If contamination is found, it can usually be removed
easily with "Count Off". If it cannot be removed,
contact the RSO to obtain shielding materials.
- 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.
- Send a Radiation Contamination Survey
Report to the RSO.
(Call the RSO if you have any questions about where to
survey, or how to fill out the form.)
- Wash your hands thoroughly.
- Bring the waste to the Radiation Safety Office
frequently. We accept waste every Friday. Please call
656-2570 for an appointment.
º Any questions about these procedures ?
Call the Radiation Safety Office, 656-2570 º
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 125I 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