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Radionuclide Dosimetric Data Sheets
Iodine-121
Summary data
General
Classification
Isotope: I-121
Atomic number (Z): 53
Mass number (A): 121
Neutron number (N): 68
Radioactive decay
Decay modes: β+, Electron capture
Half-life: 2.12 [h]
Decay constant: 9.0821e-05 [1/s]
Daughters: Te-121 (99.7%), Te-121m (0.286%)
Radioactive daughters: Te-121, Te-121m
Dosimetric constants
Mean alpha energy: 0.0 [MeV]
Mean electron energy: 0.06649 [MeV]
Mean photon energy: 0.39947 [MeV]
Air kerma rate constant, Γ10: 1.479e-17 [Gy·m2/Bq·s]
Air kerma coefficient, Kair: 1.864e-17 [Gy·m2/Bq·s]
Equilibrium dose constant for weakly-penetrating radiations (α and/or
electrons), Δwp: 1.065e-14 [Gy·kg/Bq·s]
Equilibrium dose constant for alphas, Δα: 0.000e+00
[Gy·kg/Bq·s]
Equilibrium dose constant for betas/electrons, Δβ-,β+,e-:
1.065e-14 [Gy·kg/Bq·s]
Equilibrium dose constant for photons, Δp: 6.400e-14
[Gy·kg/Bq·s]
Dose point kernels (plot)
Dose point kernel source: Graves, et al. Medical Physics. 2019 Nov.; 46(11):5284-5293.
Note: Bins are spaced every 0.1 mm until a radius of 10 cm, and every 1 mm until a radius of 2 m.
Download tabulated dose point kernel file here: www.mirdsoft.org/products/MIRDspecs/I-121 DPK.csv
Summary spectra (plot)
Spectra source: ICRP Publication 107: Nuclear Decay Data for Dosimetric Calculations. Ann. ICRP 2008, 38 (3).
Download tabulated summary spectra file here: www.mirdsoft.org/products/MIRDspecs/I-121 Summary Spectrum.csv
Beta spectra (plot)
Spectra source: ICRP Publication 107: Nuclear Decay Data for Dosimetric Calculations. Ann. ICRP 2008, 38 (3).
Download tabulated beta spectra file here: www.mirdsoft.org/products/MIRDspecs/I-121 Beta Spectrum.csv
Tabulated data
Summary spectra (table)
Spectra source: ICRP Publication 107: Nuclear Decay Data for Dosimetric Calculations. Ann. ICRP 2008, 38 (3).
Note: Radiations with yield < 0.01 are excluded from the table, but are available in the linked *.csv data.
Download tabulated summary spectra file here: www.mirdsoft.org/products/MIRDspecs/I-121 Summary Spectrum.csv
|
Energy [MeV] |
Yield [#/nt] if > 0.01 |
Radiation type |
|
1.36107e-05 |
1.260e+01 |
X-ray |
|
3.75695e-03 |
3.330e-02 |
X-ray |
|
4.02446e-03 |
1.914e-02 |
X-ray |
|
2.71868e-02 |
2.122e-01 |
X-ray |
|
2.74652e-02 |
3.951e-01 |
X-ray |
|
3.09378e-02 |
3.638e-02 |
X-ray |
|
3.09901e-02 |
7.055e-02 |
X-ray |
|
3.16841e-02 |
1.481e-02 |
X-ray |
|
2.12200e-01 |
8.405e-01 |
Gamma |
|
4.75280e-01 |
1.020e-02 |
Gamma |
|
5.11000e-01 |
1.986e-01 |
Annihilation photon |
|
5.32080e-01 |
6.070e-02 |
Gamma |
|
5.98740e-01 |
1.467e-02 |
Gamma |
|
4.64603e-01 |
9.654e-02 |
Positron |
|
2.29235e-05 |
6.157e+00 |
Auger electron |
|
2.49265e-05 |
2.056e+00 |
Auger electron |
|
1.21032e-04 |
7.083e-01 |
Auger electron |
|
2.95344e-04 |
1.311e-01 |
Auger electron |
|
4.49477e-04 |
1.585e+00 |
Auger electron |
|
5.41137e-04 |
6.107e-02 |
Auger electron |
|
3.08441e-03 |
6.225e-01 |
Auger electron |
|
3.67848e-03 |
1.763e-01 |
Auger electron |
|
4.29478e-03 |
1.247e-02 |
Auger electron |
|
2.26653e-02 |
6.859e-02 |
Auger electron |
|
2.65056e-02 |
3.021e-02 |
Auger electron |
|
1.80395e-01 |
6.387e-02 |
Conversion electron |
Useful Links
Isotope decay characteristics are periodically updated as better measurements can be made - changes that may not be reflected on this page. Please see useful links:
National Nuclear Data Center (NNDC): https://www.nndc.bnl.gov/nudat3/mird/
International Atomic Energy Agency (IAEA) Livechart: https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html
Reference Links
ICRP Report 107: https://www.icrp.org/publication.asp?id=ICRP%20Publication%20107
Graves et al. Dose Point Kernels: https://doi.org/10.1002/mp.13789
MIRD Decay Schemes 2nd Edition: https://sites.snmmi.org/SNMMI-MAIN/iCore/Store/StoreLayouts/Item_Detail.aspx?iProductCode=0-932004-80-6
MIRDsoft MIRDspecs version 20250101 (www.mirdsoft.org)
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