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Iodine 125

Gamma Max Half Life
0.035 MeV 59.4 days

In Use

The following quantities will give a dose rate of 2 mSv/h without shielding.

  • If handled at distances of 10 cm or more 500 MBq
  • If handled at distances of less than 10 cm 5 MBq

Note that these quantities may be handled for a maximum of 15 minutes per day, five days a week, before the dose rate to the fingers is exceeded.

Effective Dose Coefficients

Inhalation coefficient

Ingestion coefficient

Skin dose coefficient

5.3 x 10-9 Sv.Bq-1 - 1μm AMAD

1.5 x 10-8 Sv.Bq-1

0.0 Gy.s-1 per


The limit for classifying as a controlled area on the basis of radiation dose rate alone is very high. However, with this isotope the overruling factor is the internal hazard limit, which is 3 MBq. Above this quantity the laboratory must be classified as a controlled area.

If the total quantity of iodine - 125 in the laboratory is over 1MBq it is necessary to classify the laboratory as a supervised area.

*3 MBq if inhaled would give rise to an effective dose of 15 mSv.