All tools

Nuclide reference

Te-121m — Tellurium-121m

The half-life of Te-121m is 164.2 d. Main decay mode: isomeric transition to Te-121 (88.6%).

Identification

Element
Tellurium (Te)
Atomic number Z
52
Mass number A
121
State
Radioactive

Key quantities

Half-life
164.2 d
Specific activity
2.432e+14 Bq/g
Gamma constant Γ
—
A1 / A2 for transport (SSR-6, НП-053-16)
5 TBq / 3 TBq
D-value (НП-067-24)
0.1 TBq

Decay modes

  • isomeric transition → Te-121 — 88.6 %
  • β⁺ decay / electron capture → Sb-121 — 11.4 %

Main gamma lines

Energy, keVYield, %
212.18981.51
573.139 (Te-121)80.65
26.359 (Te-121) · X-ray line40.97
26.111 (Te-121) · X-ray line21.96
507.591 (Te-121)17.74
1,102.152.538
470.472 (Te-121)1.411
37.1380.9416
65.548 (Te-121)0.2605
37.138 (Te-121)0.1203

Includes daughter nuclides in equilibrium: Te-121 (yield per decay of Te-121m); the emitting nuclide is in brackets. Equilibrium is reached in about 150 d.

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.

Tellurium-121m (Te-121m) — reference data

What is in the card

This card gathers the key data of radionuclide Te-121m 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 Te-121m 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.