Notation: mass number as a left superscript (e.g., ⁴⁰K).
Columns: Isotope | Z | A | Stable? | Half‑life | Decay mode(s) | Daughter | Radiation | Origin | Uses | Notes.
Backbone: evaluated data compiled in Isotopes of potassium (NUBASE/ENSDF/AME cross‑linked); individual nuclides cross‑checked in NNDC/KAERI and application‑specific literature. (Wikipedia, National Nuclear Data Center, KAERI Nuclear Data Center)
| Isotope | Z | A | Stable? | Half‑life | Decay mode(s) | Daughter | Radiation | Origin | Uses | Notes |
|---|---|---|---|---|---|---|---|---|---|---|
| ³¹K | 19 | 31 | Unstable (unbound) | < 10 ps | 3p | ²⁸S | prompt p | Synthetic | Research (extreme p‑rich; 3‑proton emission) | First observed 2019; three‑proton decay in flight. (Physical Review Links, arXiv) |
| ³⁴K | 19 | 34 | Unstable (unbound) | prompt | p | ³³Ar | p | Synthetic | Research (proton dripline) | Proton‑unbound resonance. (Wikipedia) |
| ³⁵K | 19 | 35 | Unstable | 175.2(19) ms | β⁺ 99.63%; β⁺p 0.37% | ³⁵Ar; ³⁴Cl | β⁺; delayed p | Synthetic | β⁺/β‑delayed‑p studies | — (Wikipedia) |
| ³⁶K | 19 | 36 | Unstable | 341(3) ms | β⁺ 99.95%; β⁺p 0.048%; β⁺α 0.0034% | ³⁶Ar; ³⁵Cl; ³²S | β⁺; delayed p/α | Synthetic | Reaction/decay studies | Tiny β⁺α branch to ³²S. (Wikipedia) |
| ³⁷K | 19 | 37 | Unstable | 1.23651(94) s | β⁺ | ³⁷Ar | β⁺ | Synthetic | β⁺ spectroscopy | — (Wikipedia) |
| ³⁸K | 19 | 38 | Unstable | 7.651(19) min | ε/β⁺ → ³⁸Ar | ³⁸Ar | X‑rays (EC), β⁺; γ from ³⁸Ar* | Synthetic | Blood‑flow tracer in physiology (short‑lived K analog) | KAERI: EC decay; PubChem notes tracer use. ³⁸ᵐ¹K 924 ms (IT/ε); ³⁸ᵐ²K 21.95 µs (IT). (KAERI Nuclear Data Center, PubChem, National Nuclear Data Center) |
| ³⁹K | 19 | 39 | Stable | — | — | — | — | Natural (93.26%) | Stable‑isotope geochemistry/biology (δ⁴¹K = ⁴¹K/³⁹K) | Used with ⁴¹K to trace K cycling in Earth & biology. (U.S. Geological Survey, PMC) |
| ⁴⁰K | 19 | 40 | Unstable (primordial) | 1.248(3)×10⁹ y | β⁻ 89.28% → ⁴⁰Ca; EC 10.72% → ⁴⁰Ar (β⁺ ~0.001%) | ⁴⁰Ca; ⁴⁰Ar | β⁻; γ 1460.8 keV (from EC branch) | Natural trace (0.0117%) | K–Ar / ⁴⁰Ar/³⁹Ar geochronology; total‑body K & body composition via natural ⁴⁰K; calibration source | Standard values & 1460.8 keV γ yield documented. (Wikipedia, advlabs.aapt.org) |
| ⁴¹K | 19 | 41 | Stable | — | — | — | — | Natural (6.73%) | δ⁴¹K in geochem/biomed; enriched spikes | Pair with ³⁹K for high‑precision δ⁴¹K by MC‑ICP‑MS. (U.S. Geological Survey) |
| ⁴²K | 19 | 42 | Unstable | 12.355(7) h | β⁻ → ⁴²Ca | ⁴²Ca | β⁻; γ from ⁴²Ca* | Activation & synthetic (from ⁴²Ar) | Human K‑turnover tracer (whole‑body counting) | Classic tracer in human/plant studies. (Wikipedia, KAERI Nuclear Data Center, PubMed) |
| ⁴³K | 19 | 43 | Unstable | 22.3(1) h | β⁻ → ⁴³Ca | ⁴³Ca | β⁻; γ from ⁴³Ca* | Synthetic | Historic myocardial perfusion imaging; tracer dilution | Used clinically in the 1970s with ⁸¹Rb. ⁴³ᵐK: 200 ns (IT). (PubMed, circ.ahajournals.org) |
| ⁴⁴K | 19 | 44 | Unstable | 22.13(19) min | β⁻ → ⁴⁴Ca | ⁴⁴Ca | β⁻ | Synthetic | β/γ spectroscopy | — (Wikipedia) |
| ⁴⁵K | 19 | 45 | Unstable | 17.8(6) min | β⁻ → ⁴⁵Ca | ⁴⁵Ca | β⁻ | Synthetic | Activation studies | — (Wikipedia) |
| ⁴⁶K | 19 | 46 | Unstable | 96.30(8) s | β⁻ → ⁴⁶Ca | ⁴⁶Ca | β⁻ | Synthetic | Structure near N = 27–28 | — (Wikipedia) |
| ⁴⁷K | 19 | 47 | Unstable | 17.38(3) s | β⁻ → ⁴⁷Ca | ⁴⁷Ca | β⁻ | Synthetic | Decay studies | — (Wikipedia) |
| ⁴⁸K | 19 | 48 | Unstable | 6.83(14) s | β⁻ 98.86%; β⁻,n 1.14% | ⁴⁸Ca; ⁴⁷Ca | β⁻; delayed n | Synthetic | β‑delayed‑n benchmarks | — (Wikipedia) |
| ⁴⁹K | 19 | 49 | Unstable | 1.26(5) s | β⁻,n 86%; β⁻ 14% | ⁴⁸Ca; ⁴⁹Ca | β⁻; delayed n | Synthetic | Neutron‑rich decay | — (Wikipedia) |
| ⁵⁰K | 19 | 50 | Unstable | 472(4) ms | β⁻ 71.4%; β⁻,n 28.6% (β⁻,2n?) | ⁵⁰Ca; ⁴⁹Ca (⁴⁸Ca) | β⁻; delayed n | Synthetic | Structure far from stability | ⁵⁰ᵐK: 125 ns (IT). (Wikipedia) |
| ⁵¹K | 19 | 51 | Unstable | 365(5) ms | β⁻,n 65%; β⁻ 35% (β⁻,2n?) | ⁵⁰Ca; ⁵¹Ca (⁴⁹Ca) | β⁻; delayed n | Synthetic | Dripline approach | — (Wikipedia) |
| ⁵²K | 19 | 52 | Unstable | 110(4) ms | β⁻,n 72.2%; β⁻ 25.5%; β⁻,2n 2.3% | ⁵¹Ca; ⁵²Ca; ⁵⁰Ca | β⁻; delayed n/2n | Synthetic | β‑n statistics | — (Wikipedia) |
| ⁵³K | 19 | 53 | Unstable | 30(5) ms | β⁻,n 64%; β⁻ 26%; β⁻,2n 10% | ⁵²Ca; ⁵³Ca; ⁵¹Ca | β⁻; delayed n/2n | Synthetic | Edge‑of‑stability tests | — (Wikipedia) |
| ⁵⁴K | 19 | 54 | Unstable | 10(5) ms | β⁻ (± n?) | ⁵⁴Ca (⁵³/⁵²Ca) | β⁻; delayed n? | Synthetic | Trend‑evaluated | Partly trend (#) evaluation. (Wikipedia) |
| ⁵⁵K | 19 | 55 | Unstable | ≈ 10 ms (#; > 620 ns) | β⁻? (± n/2n?) | ⁵⁵Ca (…⁵⁴/⁵³Ca) | β⁻; delayed n? | Synthetic | Heavier K observed | Trend‑estimated (#). (Wikipedia) |
| ⁵⁶K | 19 | 56 | Unstable | ≈ 5 ms (#; > 620 ns) | β⁻? (± n/2n?) | ⁵⁶Ca (…⁵⁵/⁵⁴Ca) | β⁻; delayed n? | Synthetic | Edge tests | Trend‑estimated (#). (Wikipedia) |
| ⁵⁷K | 19 | 57 | Unstable | ≈ 2 ms (#; > 400 ns) | β⁻? (± n/2n?) | ⁵⁷Ca (…⁵⁶/⁵⁵Ca) | β⁻; delayed n? | Synthetic | Most neutron‑rich well‑documented | Trend‑estimated (#). (Wikipedia) |
| ⁵⁹K | 19 | 59 | Unconfirmed | ≈ 1 ms (#) | β⁻? (± n/2n?) | ⁵⁹Ca (…⁵⁸/⁵⁷Ca) | β⁻; delayed n? | Synthetic | Reported but unconfirmed | Listed with caveat in evaluated table. (Wikipedia) |
Radiation key: β⁺/EC → annihilation γ (511 keV) and X‑rays (EC); β⁻ (electron); β⁻,n/β⁻,2n = β‑decay with 1/2 delayed neutron(s); p/3p = prompt proton(s) emission from unbound states; IT = isomeric transition γ.
Applied highlights: ⁴⁰K underpins K–Ar and ⁴⁰Ar/³⁹Ar dating and is a ubiquitous natural γ source (1460.8 keV); ⁴²K and ⁴³K were classic physiological tracers (human K turnover; myocardial perfusion), while ³⁸K has been used as a short‑lived blood‑flow tracer. (Wikipedia, advlabs.aapt.org, PubMed, circ.ahajournals.org, PubChem)
Totals — Potassium (Z = 19)
- Stable2 (³⁹K, ⁴¹K)
- Unstable (radioisotopes)23 (³¹K, ³⁴–⁴⁰K*, ⁴²–⁵⁷K; ⁴⁰K is primordial long‑lived)
- Total isotopes25 (plus ⁵⁹K unconfirmed). (Wikipedia)
Running cumulative totals (H → K, Z = 1…19)
- Cumulative total isotopes350 (prior through Ar: 325 • K: +25)
- Cumulative stable40 (prior through Ar: 38 • K: +2)
- Cumulative unstable310
Sources & cross‑checks
- Isotopes of potassium — per‑nuclide half‑lives, modes & branches (A = 31, 34–57; unconfirmed 59); natural abundances; discovery notes. (Wikipedia)
- NNDC / NuDat‑ENSDF — authoritative decay datasets and isomer details (e.g., ³⁸K EC, ³⁸ᵐ¹K 924 ms; NuDat portal). (National Nuclear Data Center)
- KAERI nuclide sheets (concise half‑life & mode): ⁴²K (12.360 h), ³⁸K (7.636 min). (KAERI Nuclear Data Center)
- ⁴⁰K: half‑life/branching and 1460.8 keV γ yield summarized in instructional and review PDFs; also geochronology context. (advlabs.aapt.org, gchron.copernicus.org)
- Physiological tracers: ⁴²K human K‑turnover (whole‑body counting, PubMed 1975); ⁴³K myocardial perfusion (JNM/Circulation 1971–76); ³⁸K blood‑flow tracer (PubChem). (PubMed, Journal of Nuclear Medicine, circ.ahajournals.org, PubChem)
- Stable K isotope geochemistry/biology (δ⁴¹K) — USGS/JAAS methods and recent applications (PNAS 2022). (U.S. Geological Survey, PMC)
Next: Calcium — Ca (Z = 20).
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