Summary data

General

Classification

Isotope: Es-255
Atomic number (Z): 99
Mass number (A): 255
Neutron number (N): 156

Radioactive decay

Decay modes: α, β-, Spontaneus fission
Half-life: 39.8 [d]
Decay constant: 2.0157e-07 [1/s]
Daughters: Fm-255 (92.0%), Bk-251 (8.0%), SF (0.0045%)
Radioactive daughters: Fm-255, Bk-251

Dosimetric constants

Mean alpha energy: 0.5116 [MeV]
Mean electron energy: 0.07366 [MeV]
Mean photon energy: 0.00068 [MeV]
Air kerma rate constant, Γ₁₀: 0.000e+00 [Gy·m²/Bq·s]
Air kerma coefficient, K_air: 1.025e-19 [Gy·m²/Bq·s]
Equilibrium dose constant for weakly-penetrating radiations (α and/or electrons), Δ_wp: 9.377e-14 [Gy·kg/Bq·s]
Equilibrium dose constant for alphas, Δ_α: 8.197e-14 [Gy·kg/Bq·s]
Equilibrium dose constant for betas/electrons, Δ_β-,β+,e-: 1.180e-14 [Gy·kg/Bq·s]
Equilibrium dose constant for photons, Δ_p: 1.089e-16 [Gy·kg/Bq·s]

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/Es-255 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/Es-255 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/Es-255 Summary Spectrum.csv

Energy [MeV]	Yield [#/nt] if > 0.01	Radiation type
7.96631e-02	9.200e-01	Beta
6.30092e+00	7.016e-02	Alpha
1.00478e-01	7.016e-02	Alpha recoil

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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