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Radionuclide Dosimetric Data Sheets

Cesium-121m

Summary data

General

Classification

Isotope:  Cs-121m
Atomic number (Z):  55
Mass number (A):  121
Neutron number (N):  66

Radioactive decay

Decay modes:  β+, Electron capture, Internal transition
Half-life:  122.0 [s]
Decay constant:  5.6815e-03 [1/s]
Daughters:  Xe-121 (83.0%), Cs-121 (17.0%)
Radioactive daughters:  Xe-121, Cs-121

Dosimetric constants

Mean alpha energy:  0.0 [MeV]
Mean electron energy:  1.34751 [MeV]
Mean photon energy:  1.18208 [MeV]
Air kerma rate constant, Γ10:  1.706e-17 [Gy·m2/Bq·s]
Air kerma coefficient, Kair:  4.514e-17 [Gy·m2/Bq·s]
Equilibrium dose constant for weakly-penetrating radiations (α and/or electrons), Δwp:  2.159e-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-:  2.159e-13 [Gy·kg/Bq·s]
Equilibrium dose constant for photons, Δp:  1.894e-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-121m 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-121m 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-121m 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-121m Summary Spectrum.csv

 

Energy [MeV]

Yield [#/nt] if > 0.01

Radiation type

1.66176e-05

3.388e+00

X-ray

2.18915e-05

1.901e+00

X-ray

4.09719e-03

1.088e-02

X-ray

2.94521e-02

6.232e-02

X-ray

2.97812e-02

1.154e-01

X-ray

3.06218e-02

2.142e-02

X-ray

3.09789e-02

3.956e-02

X-ray

3.35665e-02

1.083e-02

X-ray

3.36295e-02

2.100e-02

X-ray

1.53900e-01

1.173e-02

Gamma

1.79400e-01

3.021e-01

Gamma

1.96000e-01

2.413e-01

Gamma

2.34500e-01

4.691e-02

Gamma

2.39600e-01

1.746e-02

Gamma

2.78900e-01

1.303e-02

Gamma

2.80100e-01

1.564e-02

Gamma

2.80100e-01

3.127e-02

Gamma

3.20900e-01

2.606e-02

Gamma

4.14100e-01

2.163e-02

Gamma

4.27100e-01

2.111e-02

Gamma

4.50100e-01

1.303e-02

Gamma

4.59700e-01

1.199e-01

Gamma

5.11000e-01

1.451e+00

Annihilation photon

5.26700e-01

1.251e-02

Gamma

5.55000e-01

1.199e-02

Gamma

7.06200e-01

1.407e-02

Gamma

1.43270e+00

1.042e-02

Gamma

1.41438e+00

1.685e-02

Positron

1.67922e+00

2.006e-02

Positron

1.68765e+00

3.911e-02

Positron

1.70952e+00

1.093e-02

Positron

1.72087e+00

1.123e-02

Positron

1.76109e+00

2.006e-02

Positron

1.79355e+00

1.404e-02

Positron

1.80895e+00

1.324e-01

Positron

1.83037e+00

3.410e-02

Positron

1.91542e+00

8.726e-02

Positron

1.93367e+00

7.823e-02

Positron

1.94151e+00

1.855e-01

Positron

2.10709e-05

2.555e-01

Auger electron

2.61667e-05

5.279e-01

Auger electron

3.62396e-05

1.612e+00

Auger electron

4.14575e-05

9.015e-01

Auger electron

1.17974e-04

1.139e-01

Auger electron

1.23767e-04

1.983e-01

Auger electron

3.19845e-04

3.741e-02

Auger electron

3.52105e-04

2.416e-02

Auger electron

5.05091e-04

4.422e-01

Auger electron

5.28931e-04

2.447e-01

Auger electron

6.17233e-04

2.530e-02

Auger electron

6.54643e-04

1.611e-02

Auger electron

3.32460e-03

1.743e-01

Auger electron

3.44242e-03

9.525e-02

Auger electron

3.84400e-03

7.839e-02

Conversion electron

4.00175e-03

5.171e-02

Auger electron

4.16445e-03

2.937e-02

Auger electron

2.44715e-02

1.752e-02

Auger electron

3.25150e-02

8.315e-02

Conversion electron

6.28151e-02

2.924e-02

Conversion electron

6.34939e-02

3.271e-02

Conversion electron

6.75093e-02

1.578e-02

Conversion electron

1.44844e-01

4.252e-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

 

 

 

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