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Radionuclide Safety Data Sheets

Iodine - 125(125I)

PHYSICAL DATA

Gamma Energies:
(No Betas Emitted
31.0 keV (25% abundance)
35.5 keV ( 7% / 93% internally converted)
27.2 keV (39.2%)
27.4 keV (73.2%)
Specific Gamma Ray Constant:* 0.142 - 0.27 mrem/h at 1 meter per millicurie
* [Literature varies from 0.142 to 0.7 mrem/h at 1 meter per 1 mCi]

Physical Half-Life: 60.1 days
Biological Half-Life: 120-138 days (unbound iodine) - thyroid elimination
Effective Half-Life: 42 days (unbound iodine) - thyroid gland
   
Specific Activity: 17,353 curies / gram (theoretical/carrier free)
Intrinsic Specific Activity: 2,175 curies / millimole

 

RADIOLOGICAL DATA

Example: An intake of 3.15 uCi I-125 will result in an uptake by the body of approximately 2.4 uCi and an uptake by the thyroid of approximately 0.71 uCi

Skin Contamination Exposure Rate (Basal Cells): * -0- mrem/h per uCi/cm2
* [HP / April 1990 / Vol. 58 / No. 4 and Varskin (et al) calculations]

SHIELDING:
* lead foil or sheets (1/32" to 1/16" thick)
* 0.152 mm lead foil = approximately 1% transmission
* 7.2 mm lead-impregnated plastic or acrylic shield (30% by weight) << 0.1% transmission

Half-Value Layer (lead): 0.0018 cm = 0.02 mm = 0.0008"
Half-Value Layer* (water / tissue): 1.70 cm
Half-Value Layer (concrete): 0.21 cm
Tenth-Value Layer** (lead): 0.056 mm
Tenth-Value Layer (concrete): 7.30 mm

* Half-Value Layer (HVL) = amount of shielding necessary to reduce a radiation exposure rate to 1/2 (50%) of its original value.

** Tenth-Value Layer(TVL) = amount of shielding necessary to reduce a radiation exposure rate to 1/10 (10%) of its original value.

SURVEY INSTRUMENTATION:

PERSONAL RADIATION MONITORING DOSIMETERS (Whole Body and Finger Tabs): REQUIRED when handling > 5.0 millicuries of I-125 at any time.

Dose Rates from unshielded 1.0 millicurie isotropic point source of I-125:

Distance mrem/hour
1.0 cm 1560-2750
10.0 cm 15.5-27.5
100.0 cm 0.142-0.27*
6.0 in 6.5
* [Literature varies: 0.142 - 0.7 mrem/hour at 100 cm per 1 mCi]

REGULATORY COMPLIANCE INFORMATION (10 CFR 20 / Appendix B)

IODINATION PROCEDURES

GENERAL RADIOLOGICAL SAFETY INFORMATION

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