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Nuclide reference

Np-235 — Neptunium-235

The half-life of Np-235 is 1.0847 years. Main decay mode: electron capture to U-235 (100%).

Identification

Element
Neptunium (Np)
Atomic number Z
93
Mass number A
235
State
Radioactive

Key quantities

Half-life
1.0847 years
Specific activity
5.189e+13 Bq/g
Gamma constant Γ
—
A1 / A2 for transport (SSR-6, НП-053-16)
40 TBq / 40 TBq
D-value (НП-067-24)
100 TBq

Decay modes

  • electron capture → U-235 — 100 %
  • α decay → Pa-231 — 0.0026 %

Main gamma lines

Energy, keVYield, %
13.6086 · X-ray line15.1
16.9584 · X-ray line13.73
17.1850.001014
25.640.0003718
18.050.00026
84.20.0001794

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

Related calculators

DecayActivity ↔ massSource categoryDose rateA1/A2 and package type
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.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.

Neptunium-235 (Np-235) — reference data

What is in the card

This card gathers the key data of radionuclide Np-235 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 Np-235 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.