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Nuclide reference

Tl-209 — Thallium-209

The half-life of Tl-209 is 2.2 min. Main decay mode: β⁻ decay to Pb-209 (100%).

Identification

Element
Thallium (Tl)
Atomic number Z
81
Mass number A
209
State
Radioactive

Key quantities

Half-life
2.2 min
Specific activity
1.513e+19 Bq/g
Gamma constant Γ
—
D-value (НП-067-24)
—

Decay modes

  • β⁻ decay → Pb-209 — 100 %

Main gamma lines

Energy, keVYield, %
1,567.0999.81
465.1396.9
117.21184.3
74.97 · X-ray line10.51
72.807 · X-ray line6.238
920.130.6105
1,239.160.4554

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

Alpha and beta particles

RadiationEnergy, keVYield, %
β⁻, E max1,827.698.8
907.440.61
588.410.46
1,944.80.05

For β⁻ the endpoint (maximum) energy of the spectrum is given. ENDF/B-VIII.0.

Related calculators

DecayActivity ↔ massDose rate
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.

Thallium-209 (Tl-209) — reference data

What is in the card

This card gathers the key data of radionuclide Tl-209 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 Tl-209 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.