Notation. Nuclides are written with the mass number as a left superscript (e.g., ¹⁵³Gd).
Columns. Stable? refers to the ground state; “Obs.-stable” = stable by observation (decay only predicted). Half‑life and Decay mode(s) are evaluated values; Daughter is the immediate product. Radiation summarizes emissions (β⁺/β⁻/α; X/γ from EC; “p” for β‑delayed proton; “β−,n” for β‑delayed neutron). Origin sketches typical production. Uses flags M (medical), I (industrial), R (research).
Data spine. Ground‑state half‑lives, branches and daughters are from the evaluated Isotopes of gadolinium table (NUBASE/ENSDF/AME sourced, updated 2025). Natural isotopic composition is from CIAAW (2024). Application notes draw on LNHB and NIST for ¹⁵³Gd and on OECD‑NEA and peer‑reviewed reviews for neutron‑capture cross‑sections. (Wikipedia, CIAAW, Lnhb, PMC, PubMed, OSTI.gov, Nuclear Energy Agency (NEA))
Gadolinium — ground states
| Isotope | Z | A | Stable? | Half‑life | Decay mode(s) (main) | Daughter(s) | Radiation | Origin | Uses / notes |
|---|---|---|---|---|---|---|---|---|---|
| ¹³⁵Gd | 64 | 135 | No | 1.1 s (#) | β⁺; p (minor) | ¹³⁵Eu; ¹³⁴Sm | β⁺; p | Synthetic (p‑rich) | R. (Wikipedia) |
| ¹³⁶Gd | 64 | 136 | No | ≈1 s (#) | β⁺ (±p?) | ¹³⁶Eu (± ¹³⁵Sm) | β⁺ (p) | Synthetic (p‑rich) | R. (Wikipedia) |
| ¹³⁷Gd | 64 | 137 | No | 2.2 s | β⁺ (±p?) | ¹³⁷Eu (± ¹³⁶Sm) | β⁺ (p) | Synthetic (p‑rich) | R. (Wikipedia) |
| ¹³⁸Gd | 64 | 138 | No | 4.7 s | β⁺ | ¹³⁸Eu | β⁺ | Synthetic | R. (Wikipedia) |
| ¹³⁹Gd | 64 | 139 | No | 5.7 s | β⁺ (±p?) | ¹³⁹Eu (± ¹³⁸Sm) | β⁺ (p) | Synthetic | R. (Wikipedia) |
| ¹⁴⁰Gd | 64 | 140 | No | 15.8 s | β⁺ ≈67%, EC ≈33% | ¹⁴⁰Eu | β⁺; X/γ | Activation/Synth. | R. (Wikipedia) |
| ¹⁴¹Gd | 64 | 141 | No | 14 s | β⁺ (≈100%) | ¹⁴¹Eu | β⁺ | Activation/Synth. | R. (Wikipedia) |
| ¹⁴²Gd | 64 | 142 | No | 70.2 s | EC ≈52%, β⁺ ≈48% | ¹⁴²Eu | X/γ; β⁺ | Activation/Synth. | R. (Wikipedia) |
| ¹⁴³Gd | 64 | 143 | No | 39 s | β⁺ (±p?; ±α?) | ¹⁴³Eu (± ¹⁴²Sm; ± ¹³⁹Pm) | β⁺; α | Activation/Synth. | R. (Wikipedia) |
| ¹⁴⁴Gd | 64 | 144 | No | 4.47 min | β⁺ | ¹⁴⁴Eu | β⁺ | Activation/Synth. | R. (Wikipedia) |
| ¹⁴⁵Gd | 64 | 145 | No | 23.0 min | β⁺ | ¹⁴⁵Eu | β⁺ | Activation/Synth. | R. (Wikipedia) |
| ¹⁴⁶Gd | 64 | 146 | No | 48.27 d | EC | ¹⁴⁶Eu | X/γ | Activation | R. (Wikipedia) |
| ¹⁴⁷Gd | 64 | 147 | No | 38.06 h | β⁺ | ¹⁴⁷Eu | β⁺ | Activation | R. (Wikipedia) |
| ¹⁴⁸Gd | 64 | 148 | No | 86.9 y | α (theor. β⁺β⁺ possible) | ¹⁴⁴Sm | α | Synthetic (long‑lived) | Proposed RTG fuel (production not economical). (Wikipedia) |
| ¹⁴⁹Gd | 64 | 149 | No | 9.28 d | β⁺; α (~4.3×10⁻⁴ %) | ¹⁴⁹Eu; ¹⁴⁵Sm | β⁺; α | Activation | R (rare α branch). (Wikipedia) |
| ¹⁵⁰Gd | 64 | 150 | No | 1.79×10⁶ y | α (theor. β⁺β⁺ possible) | ¹⁴⁶Sm | α | Synthetic (long‑lived) | Long‑lived tracer. (Wikipedia) |
| ¹⁵¹Gd | 64 | 151 | No | 123.9 d | EC; α (~1.1×10⁻⁶ %) | ¹⁵¹Eu; ¹⁴⁷Sm | X/γ; α | Activation | R. (Wikipedia) |
| ¹⁵²Gd | 64 | 152 | No (primordial) | 1.08×10¹⁴ y | α | ¹⁴⁸Sm | α | Natural (primordial radioisotope) | Rare‑decay & 0νECEC searches. (Wikipedia, arXiv) |
| ¹⁵³Gd | 64 | 153 | No | 240.6 d | EC (100%) | ¹⁵³Eu | X/γ (97 & 103 keV prominent) | Activation | I/M: γ calibration; DEXA/DPA line sources; SPECT attenuation. (Lnhb, PMC, Stanford Environmental Health & Safety) |
| ¹⁵⁴Gd | 64 | 154 | Obs.-stable | — | — | — | — | Natural | Stable isotope. (Wikipedia) |
| ¹⁵⁵Gd | 64 | 155 | Obs.-stable | — | — | — | — | Natural | High n‑capture σ (~6.1×10⁴ b). Absorber. (OSTI.gov) |
| ¹⁵⁶Gd | 64 | 156 | Stable | — | — | — | — | Natural | Stable isotope. (Wikipedia) |
| ¹⁵⁷Gd | 64 | 157 | Stable | — | — | — | — | Natural | Highest thermal n‑capture σ among stable nuclides (~2.54×10⁵ b). Absorber. (PubMed, OSTI.gov) |
| ¹⁵⁸Gd | 64 | 158 | Stable | — | — | — | — | Natural | Stable isotope. (Wikipedia) |
| ¹⁵⁹Gd | 64 | 159 | No | 18.479 h | β⁻ | ¹⁵⁹Tb | β⁻ | Fission product | R. (Wikipedia) |
| ¹⁶⁰Gd | 64 | 160 | Obs.-stable | — | (double‑β⁻ predicted; T½ > 3.1×10¹⁹ y limit) | — (→¹⁶⁰Dy) | — | Natural | Double‑β searches (no observation). (Wikipedia) |
| ¹⁶¹Gd | 64 | 161 | No | 3.646 min | β⁻ | ¹⁶¹Tb | β⁻ | Fission product | Parent of ¹⁶¹Tb (theranostics R). (Wikipedia, ScienceDirect) |
| ¹⁶²Gd | 64 | 162 | No | 8.4 min | β⁻ | ¹⁶²Tb | β⁻ | Fission product | R. (Wikipedia) |
| ¹⁶³Gd | 64 | 163 | No | 68 s | β⁻ | ¹⁶³Tb | β⁻ | Fission product | R. (Wikipedia) |
| ¹⁶⁴Gd | 64 | 164 | No | 45 s | β⁻ | ¹⁶⁴Tb | β⁻ | Fission product | R. (Wikipedia) |
| ¹⁶⁵Gd | 64 | 165 | No | 11.6 s | β⁻ | ¹⁶⁵Tb | β⁻ | Fission product | R. (Wikipedia) |
| ¹⁶⁶Gd | 64 | 166 | No | 5.1 s | β⁻ | ¹⁶⁶Tb | β⁻ | Fission product | R. (Wikipedia) |
| ¹⁶⁷Gd | 64 | 167 | No | 4.2 s | β⁻ | ¹⁶⁷Tb | β⁻ | Fission product | R. (Wikipedia) |
| ¹⁶⁸Gd | 64 | 168 | No | 3.03 s | β⁻ | ¹⁶⁸Tb | β⁻ | Fission product | R. (Wikipedia) |
| ¹⁶⁹Gd | 64 | 169 | No | 750 ms | β⁻; β−,n (<0.7%) | ¹⁶⁹Tb; ¹⁶⁸Tb | β⁻; n | In‑flight fission | R. (Wikipedia) |
| ¹⁷⁰Gd | 64 | 170 | No | 675 ms | β⁻; β−,n (<3%) | ¹⁷⁰Tb; ¹⁶⁹Tb | β⁻; n | In‑flight fission | R. (Wikipedia) |
| ¹⁷¹Gd | 64 | 171 | No | 392 ms | β⁻; β−,n (<10%) | ¹⁷¹Tb; ¹⁷⁰Tb | β⁻; n | In‑flight fission | R. (Wikipedia) |
| ¹⁷²Gd | 64 | 172 | No | 163 ms | β⁻; β−,n (<50%) | ¹⁷²Tb; ¹⁷¹Tb | β⁻; n | In‑flight fission | R. (Wikipedia) |
Primary table source: evaluated gadolinium isotope list (half‑lives/branches/daughters). “#” indicates values assisted by trends of neighboring nuclides. (Wikipedia)
Selected isomers (diagnostic/structure interest)
- ¹⁴¹ᵐGd — 24.5 s, β⁺ (≈89%) → ¹⁴¹Eu / IT (≈11%) → ¹⁴¹Gd; fast‑timing level scheme near N=77. (Wikipedia)
- ¹⁴³ᵐGd — 110.0 s, β⁺ → ¹⁴³Eu; long‑lived isomer in the p‑rich region. (Wikipedia)
- ¹⁴⁵ᵐGd — 85 s, IT 94% → ¹⁴⁵Gd / β⁺ 6% → ¹⁴⁵Eu; spin‑trap useful for γ‑spectroscopy. (Wikipedia)
- ¹⁵³ᵐ¹Gd — 3.5 µs, IT → ¹⁵³Gd (medical calibration nuclide); ¹⁵³ᵐ²Gd — 76 µs, IT → ¹⁵³Gd. (Wikipedia)
Natural isotopic composition (terrestrial Gd — CIAAW 2024)
Amount fractions: ¹⁵²Gd 0.00204(2) (primordial α‑emitter), ¹⁵⁴Gd 0.02187(9), ¹⁵⁵Gd 0.14828(60), ¹⁵⁶Gd 0.20493(22), ¹⁵⁷Gd 0.15657(17), ¹⁵⁸Gd 0.24820(20), ¹⁶⁰Gd 0.21811(28). (Standard atomic weight revised in 2024 to Aᵣ(Gd)=157.249(2).) (CIAAW)
Applied & research highlights (Gd)
- Neutron absorbers / burnable poisons. ¹⁵⁷Gd possesses the highest thermal neutron‑capture cross‑section of any stable nuclide (≈ 2.54×10⁵ barns); ¹⁵⁵Gd is also enormous (≈ 6.1×10⁴ barns). Gadolinium oxides are widely used as burnable absorbers in PWR/BWR fuel and as shutdown poisons (e.g., CANDU). (PubMed, OSTI.gov, Nuclear Energy Agency (NEA))
- Calibration / imaging. ¹⁵³Gd (240.6 d, EC) emits strong 97 keV & 103 keV γ/X lines, making it a workhorse line source for γ‑spectrometer calibration, DEXA/DPA bone densitometry (historical and reference use), and SPECT attenuation correction. (Lnhb, PMC, Stanford Environmental Health & Safety, NIST)
- Rare‑decay physics. ¹⁵²Gd is pursued for resonant neutrinoless double‑electron capture (current limit T½ > 4.2×10¹² y, 90% cred.). ¹⁶⁰Gd is a double‑β⁻ candidate; experiments set T½ ≳ 10²¹ y constraints—no observation to date. (arXiv)
- Long‑lived α sources. ¹⁴⁸Gd (86.9 y) and ¹⁵⁰Gd (1.79 Ma) are notable long‑lived α‑emitters; ¹⁴⁸Gd has been discussed as an RTG fuel but is impractical to produce at scale. (Wikipedia)
- Theranostic pipeline. Short‑lived ¹⁶¹Gd (3.646 min) β⁻‑decays to ¹⁶¹Tb (6.9 d), a β⁻/Auger emitter under active study as a Lu‑177‑like therapeutic nuclide (dosimetry/half‑life refinements published 2022–2024). (Wikipedia, ScienceDirect)
Totals — Gadolinium (Z = 64)
- Ground‑state isotopes listed: 38 (A = 135–172).
- Stable (ground states): 6 (¹⁵⁴, ¹⁵⁵, ¹⁵⁶, ¹⁵⁷, ¹⁵⁸, ¹⁶⁰ — three noted as obs.-stable).
- Unstable (ground states): 32 (includes primordial ¹⁵²Gd and long‑lived ¹⁴⁸Gd/¹⁵⁰Gd).
(Counts follow the current evaluated table.) (Wikipedia)
Running cumulative totals (through Gd): add +38 total / +6 stable / +32 unstable to your ledger (after Eu: ≥1914 total, 185 stable, ≥1729 unstable) → ≥1952 total, 191 stable, ≥1761 unstable.
Sources (load‑bearing)
- Comprehensive isotope list & decay data (table above): Isotopes of gadolinium (NUBASE/ENSDF/AME compiled; updated 2025). (Wikipedia)
- Natural isotopic composition (fractions & remarks): CIAAW — Isotopic Compositions of the Elements 2024 (Gd page). (CIAAW)
- ¹⁵³Gd decay data & γ lines: LNE‑LNHB Table de Radionucléides; NIST 2023 standardization study; practical RSDS (Stanford) with line list. (Lnhb, PMC, Stanford Environmental Health & Safety)
- Neutron‑capture cross‑sections & absorber use: Mughabghab values and recent reviews; OECD‑NEA note on Gd‑155/‑157 and industry use. (OSTI.gov, PubMed, Nuclear Energy Agency (NEA))
- Rare‑decay searches: Gd‑152 0νECEC (Gran Sasso); Gd‑160 2β constraints. (arXiv)
Next element: Terbium — Tb (Z = 65).