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Nuclide reference

I-125 — Iodine-125

The half-life of I-125 is 59.4 d. Main decay mode: electron capture to Te-125 (100%).

Identification

Element
Iodine (I)
Atomic number Z
53
Mass number A
125
State
Radioactive

Key quantities

Half-life
59.4 d
Specific activity
6.507e+14 Bq/g
Gamma constant Γ (H*(10))
0.03507 µSv·m²/(MBq·h)
Dose rate, 1 GBq at 1 m
≈ 35.1 µSv/h
A1 / A2 for transport (SSR-6, НП-053-16)
20 TBq / 3 TBq
D-value (НП-067-24)
0.2 TBq

Decay modes

  • electron capture → Te-125 — 100 %

Main gamma lines

Energy, keVYield, %
27.472 · X-ray line74.66
27.202 · X-ray line40.11
35.49256.68

Lines of the bare nuclide (ENDF/B-VIII.0), without daughter ingrowth.

Related calculators

DecayActivity ↔ massSource categoryDose rateA1/A2 and package type

Other isotopes of this element

I-123I-124I-129I-131
Reference data vs computed valuesHalf-life, gamma lines and D-value are reference data (ENDF/B-VIII.0, НП-067-24).Gamma constant Γ is H*(10) at 1 m computed from ICRP-107 spectra (NIST µ_en/ρ, ICRP-74 Table A.21) including short-lived progeny in equilibrium (e.g. Cs-137/Ba-137m, Ra-226 series); specific activity uses molar mass M ≈ mass number A.Dose rate example: point source, no shielding or scatter, Ḣ = Γ·A/r².K-series X-ray energies are from NIST SRD 128 (Deslattes et al., 2003): in ENDF/B-VIII.0 they are given to 1 % and shifted by up to 0.7 keV for heavy elements. L-series lines and all yields are ENDF/B-VIII.0.

Iodine-125 (I-125) — reference data

What is in the card

This card gathers the key data of radionuclide I-125 in one place: half-life, decay modes, main gamma lines, alpha and beta particle energies, gamma constant, specific activity and the D-value for source categorization. Decay and emission data are from ENDF/B-VIII.0; the D-value follows NP-067-24; the gamma constant is the ambient dose equivalent H*(10) at 1 m, computed from ICRP-107 spectra.

How to use the data

Half-life and specific activity let you recalculate the activity of a I-125 source to the delivery or disposal date — use the decay calculator. Gamma lines with yields identify the nuclide from a spectrum and pick the line for gamma spectrometry; the gamma constant Γ gives the dose rate at a distance, while the D-value and A1/A2 set the source category and the package type for transport.