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Radionuclide Dosimetric Data Sheets
Cesium-121
Summary data
General
Classification
Isotope: Cs-121
Atomic number (Z): 55
Mass number (A): 121
Neutron number (N): 66
Radioactive decay
Decay modes: β+, Electron capture
Half-life: 155.0 [s]
Decay constant: 4.4719e-03 [1/s]
Daughters: Xe-121 (100.0%)
Radioactive daughters: Xe-121
Dosimetric constants
Mean alpha energy: 0.0 [MeV]
Mean electron energy: 1.73905 [MeV]
Mean photon energy: 1.17327 [MeV]
Air kerma rate constant, Γ10: 9.979e-18 [Gy·m2/Bq·s]
Air kerma coefficient, Kair: 4.455e-17 [Gy·m2/Bq·s]
Equilibrium dose constant for weakly-penetrating radiations (α and/or
electrons), Δwp: 2.786e-13 [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-:
2.786e-13 [Gy·kg/Bq·s]
Equilibrium dose constant for photons, Δp: 1.880e-13
[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/Cs-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/Cs-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/Cs-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/Cs-121 Summary Spectrum.csv
|
Energy [MeV] |
Yield [#/nt] if > 0.01 |
Radiation type |
|
1.66174e-05 |
2.570e+00 |
X-ray |
|
2.94521e-02 |
4.618e-02 |
X-ray |
|
2.97812e-02 |
8.553e-02 |
X-ray |
|
3.36295e-02 |
1.557e-02 |
X-ray |
|
8.59000e-02 |
2.065e-02 |
Gamma |
|
1.53900e-01 |
1.515e-01 |
Gamma |
|
1.59700e-01 |
1.665e-02 |
Gamma |
|
1.79400e-01 |
2.697e-02 |
Gamma |
|
1.96000e-01 |
2.464e-02 |
Gamma |
|
2.39600e-01 |
7.726e-02 |
Gamma |
|
2.70200e-01 |
1.665e-02 |
Gamma |
|
2.95800e-01 |
1.432e-02 |
Gamma |
|
3.55900e-01 |
2.331e-02 |
Gamma |
|
4.27100e-01 |
3.630e-02 |
Gamma |
|
5.11000e-01 |
1.786e+00 |
Annihilation photon |
|
5.53000e-01 |
1.199e-02 |
Gamma |
|
6.19900e-01 |
1.132e-02 |
Gamma |
|
6.61100e-01 |
1.166e-02 |
Gamma |
|
1.43270e+00 |
1.332e-02 |
Gamma |
|
1.65879e+00 |
1.100e-02 |
Positron |
|
1.67805e+00 |
1.620e-02 |
Positron |
|
1.69474e+00 |
2.200e-02 |
Positron |
|
1.71413e+00 |
1.550e-02 |
Positron |
|
1.79437e+00 |
3.859e-02 |
Positron |
|
1.80511e+00 |
3.379e-02 |
Positron |
|
1.83884e+00 |
3.539e-02 |
Positron |
|
1.89374e+00 |
9.198e-02 |
Positron |
|
1.93441e+00 |
1.170e-01 |
Positron |
|
2.00747e+00 |
4.899e-01 |
Positron |
|
2.61519e-05 |
4.001e-01 |
Auger electron |
|
3.62372e-05 |
1.222e+00 |
Auger electron |
|
1.23828e-04 |
1.502e-01 |
Auger electron |
|
3.17372e-04 |
2.775e-02 |
Auger electron |
|
5.05044e-04 |
3.357e-01 |
Auger electron |
|
6.17087e-04 |
1.920e-02 |
Auger electron |
|
3.32390e-03 |
1.323e-01 |
Auger electron |
|
4.00089e-03 |
3.923e-02 |
Auger electron |
|
2.44715e-02 |
1.298e-02 |
Auger electron |
|
5.13440e-02 |
2.294e-02 |
Conversion electron |
|
1.19344e-01 |
4.556e-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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