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Isotopes of potassium
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Potassium () has 25 known isotopes from to as well as , as well as an unconfirmed report of . Three of those isotopes occur naturally: the two stable forms (93.26%) and (6.72%), and the long-lived radioisotope (0.012%).
Naturally occurring radioactive decays with a half-life of 1.248×109 years. 89% of those decays are to stable by beta decay, whilst 11% are to by either electron capture or positron emission. This latter decay branch has produced an isotopic abundance of argon on Earth which differs greatly from that seen in gas giants and stellar spectra. has the longest known half-life for any positron-emitting nuclide. The long half-life of this primordial radioisotope is caused by a highly spin-forbidden transition: has a nuclear spin of 4, while both of its decay daughters are even–even isotopes with spins of 0.
occurs in natural potassium in sufficient quantity that large bags of potassium chloride commercial salt substitutes can be used as a radioactive source for classroom demonstrations. is the largest source of natural radioactivity in healthy animals and humans, greater even than . In a human body of 70 kg mass, about 4300 nuclei of decay per second.
The decay of to is used in potassium-argon dating of rocks. Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic that has accumulated. has also been extensively used as a radioactive tracer in studies of weathering.
All other potassium isotopes have half-lives under a day, most under a minute. The unbound was discovered in 2019 and emits three protons; its half-life was measured to be shorter than 10 picoseconds.
Stable potassium isotopes have been used for several nutrient cycling studies since potassium is a macronutrient required for life.
List of isotopes
Potassium-32
|-id=Potassium-31 | | 31.03678(32)# | | p | 30Ar | 3/2+# | | |-id=Potassium-34 | 34K | 33.998404(18) | | p | 33Ar | | | |-id=Potassium-35 | β+ (99.63%)
| 35Ar |
|---|
| β+, p (0.37%) |
| 34Cl |
| -id=Potassium-36 |
| β+ (99.95%) |
| 36Ar |
| - |
| β+, p (0.048%) |
| 35Cl |
| - |
| β+, α (0.0034%) |
| 32S |
| -id=Potassium-37 |
| 37K |
| 36.97337589(10) |
| 1.23651(94) s |
| β+ |
| 37Ar |
| 3/2+ |
| | |-id=Potassium-38 | 38K | 37.96908111(21) | 7.651(19) min | β+ | 38Ar | 3+ | | |-id=Potassium-38m1 | β+ (99.97%)
| 38Ar |
|---|
| IT (0.0330%) |
| 38K |
| -id=Potassium-38m2 |
| 21.95(11) μs |
| IT |
| 38K |
| (7)+ |
| | |-id=Potassium-39 | 39K | 38.9637064848(49) | 3/2+ | 0.932581(44) | |- | β− (89.28%)
| 40Ca |
|---|
| EC (10.72%) |
| - |
| - |
| β+ (0.001%){{Cite journal |
| -id=Potassium-40m |
| 336(12) ns |
| IT |
| 40K |
| 0+ |
| | |-id=Potassium-41 | 41K | 40.9618252561(40) | 3/2+ | 0.067302(44) | |-id=Potassium-42 | 42K | 41.96240231(11) | 12.355(7) h | β− | 42Ca | 2− | | |-id=Potassium-43 | 43K | 42.96073470(44) | 22.3(1) h | β− | 43Ca | 3/2+ | | |-id=Potassium-43m | 200(5) ns | IT | 43K | 7/2− | | |-id=Potassium-44 | 44K | 43.96158698(45) | 22.13(19) min | β− | 44Ca | 2− | | |-id=Potassium-45 | 45K | 44.96069149(56) | 17.8(6) min | β− | 45Ca | 3/2+ | | |-id=Potassium-46 | 46K | 45.96198158(78) | 96.30(8) s | β− | 46Ca | 2− | | |-id=Potassium-47 | 47K | 46.9616616(15) | 17.38(3) s | β− | 47Ca | 1/2+ | | |-id=Potassium-48 | β− (98.86%)
| 48Ca |
|---|
| β−, n (1.14%) |
| 47Ca |
| -id=Potassium-49 |
| β−, n (86%) |
| 48Ca |
| - |
| β− (14%) |
| 49Ca |
| -id=Potassium-50 |
| β− (71.4%) |
| 50Ca |
| - |
| β−, n (28.6%) |
| 49Ca |
| - |
| β−, 2n? |
| 48Ca |
| -id=Potassium-50m |
| 125(40) ns |
| IT |
| 50K |
| (2−) |
| | |-id=Potassium-51 | β−, n (65%)
| 50Ca |
|---|
| β− (35%) |
| 51Ca |
| - |
| β−, 2n? |
| 49Ca |
| -id=Potassium-52 |
| β−, n (72.2%) |
| 51Ca |
| - |
| β− (25.5%) |
| 52Ca |
| - |
| β−, 2n (2.3%) |
| 50Ca |
| -id=Potassium-53 |
| β−, n (64%) |
| 52Ca |
| - |
| β− (26%) |
| 53Ca |
| - |
| β−, 2n (10%) |
| 51Ca |
| -id=Potassium-54 |
| β− |
| 54Ca |
| - |
| β−, n? |
| 53Ca |
| - |
| β−, 2n? |
| 52Ca |
| -id=Potassium-55 |
| [620 ns] |
| β−? |
| 55Ca |
| - |
| β−, n? |
| 54Ca |
| - |
| β−, 2n? |
| 53Ca |
| -id=Potassium-56 |
| [620 ns] |
| β−? |
| 56Ca |
| - |
| β−, n? |
| 55Ca |
| - |
| β−, 2n? |
| 54Ca |
| -id=Potassium-57 |
| [400 ns] |
| β−? |
| 57Ca |
| - |
| β−, n? |
| 56Ca |
| - |
| β−, 2n? |
| 55Ca |
| -id=Potassium-59 |
| [400 ns] |
| β−? |
| 59Ca |
| - |
| β−, n? |
| 58Ca |
| - |
| β−, 2n? |
| 57Ca |
References
References
- (14 February 2019). "Neutron Drip Line in the Ca Region from Bayesian Model Averaging". Physical Review Letters.
- Of longer ones, only 50V and 138La are theoretically capable of it, but they are still more forbidden and have very low energy release.
- "The Radioactivity of the Normal Adult Body". rerowland.com.
- (6 September 2019). "A peculiar atom shakes up assumptions of nuclear structure". Nature.
- Kostyleva, D.. (2019). "Towards the Limits of Existence of Nuclear Structure: Observation and First Spectroscopy of the Isotope 31K by Measuring Its Three-Proton Decay". Physical Review Letters.
- (June 2022). "Soil potassium isotope composition during four million years of ecosystem development in Hawaiʻi".
- (2024-09-12). "Evolution of shell gaps in the neutron-poor calcium region from invariant-mass spectroscopy of 37,38Sc, 35Ca, and 34K". Physical Review C.
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