Iodine-125

Iodine-125 (¹²⁵I) is a radioisotope of iodine which has uses in biological assays and in radiation therapy to treat prostate cancer and brain tumors. Its half-life is around 60 days and it emits gamma-rays with maximum energies of 35 keV, some of which are internally converted to x-rays. ¹²⁵I is created by the electron capture decay of ¹²⁵Xe, which is a synthetic isotope of Xenon, itself created by neutron capture of the slightly radioactive ¹²⁴Xe, which occurs naturally with an abundance of around 0.1%. Because of the synthetic production route of ¹²⁵I and its short half-life, the natural abundance is effectively 0%.

Physical Data

• Element: Iodine
• Z: 54
• A: 125
• Atomic Mass:
• Density:
• Physical state: Solid at room temperature
• Isotopic abundance: 0%

• Radioactive: Yes
• T(1/2): 59.4 days
• Decay: Electron capture to ¹²⁵Te
• Emissions: Gamma-rays at 35.5 keV. 7% emitted, 93% internally converted to:
  • 27.0 keV (113% abundance relative to 7% gamm emission)
  • 31.0 keV (26%)
  • 27-32 keV (14%)
• Half-value layer: 0.025 mm Pb

References

• Harper, P.V. ; Siemens, W.D. ; Lathrop, K.A. ; Brizel, H.E. ; Harrison, R.W. Iodine-125. Proc. Japan Conf. Radioisotopes; Vol: 4th Jan 01, 1961
• ORCBS