General | |
---|---|
Symbol | 40K |
Names | potassium-40, K-40 |
Protons | 19 |
Neutrons | 21 |
Nuclide data | |
Natural abundance | 0.0117(1)% |
Half-life | 1.251(3)×109 y |
Parent isotopes | Primordial |
Decay products | 40Ca (β−) 40Ar (EC, γ; β+) |
Isotope mass | 39.96399848(21) u |
Spin | 4− |
Excess energy | −33505keV |
Binding energy | 341523 keV |
Decay modes | |
Decay mode | Decay energy (MeV) |
β− | 1.31109 |
EC, γ | 1.5049 |
Isotopes of potassium Complete table of nuclides |
- Atomic Weight Of K
- K Ka Atomic Number
- See Full List On En.wikipedia.org
- K+1 Atomic Number
- K Atomic Number
- C Atomic Number
Potassium is a chemical element with symbol K and atomic number 19. Classified as an alkali metal, Potassium is a solid at room temperature.
Potassium-40 (40K) is a radioactive isotope of potassium which has a long half-life of 1.251×109 years. It makes up 0.012% (120 ppm) of the total amount of potassium found in nature.
Potassium-40 is a rare example of an isotope that undergoes both types of beta decay. In about 89.28% of events, it decays to calcium-40 (40Ca) with emission of a beta particle (β−, an electron) with a maximum energy of 1.31 MeV and an antineutrino. In about 10.72% of events, it decays to argon-40 (40Ar) by electron capture (EC), with the emission of a neutrino and then a 1.460 MeV gamma ray.[1] The radioactive decay of this particular isotope explains the large abundance of argon (nearly 1%) in the Earth's atmosphere, as well as prevalence of 40Ar over other isotopes. Very rarely (0.001% of events), it decays to 40Ar by emitting a positron (β+) and a neutrino.[2]
Potassium–argon dating[edit]
Decay scheme
- Alexandra knows that the atomic number of the element potassium, K, is 19. She also knows that one particular isotope of potassium has a mass number of 39. How many neutrons can be found in the nucleus of this isotope of potassium?
- K has an atomic number of 19. We need to distribute 19 electrons, knowing that there can be. 2 in an s-orbital. 6 in a p-orbital (2 in px, 2 in py and 2 in pz). 10 in a d-orbital. We won’t need f-orbitals before atomic number 58.
Potassium-40 is especially important in potassium–argon (K–Ar) dating. Argon is a gas that does not ordinarily combine with other elements. So, when a mineral forms – whether from molten rock, or from substances dissolved in water – it will be initially argon-free, even if there is some argon in the liquid. However, if the mineral contains any potassium, then decay of the 40K isotope present will create fresh argon-40 that will remain locked up in the mineral. Since the rate at which this conversion occurs is known, it is possible to determine the elapsed time since the mineral formed by measuring the ratio of 40K and 40Ar atoms contained in it.
The argon found in Earth's atmosphere is 99.6% 40Ar; whereas the argon in the Sun – and presumably in the primordial material that condensed into the planets – is mostly 36Ar, with less than 15% of 38Ar. It follows that most of the terrestrial argon derives from potassium-40 that decayed into argon-40, which eventually escaped to the atmosphere.
Contribution to natural radioactivity[edit]
The evolution of Earth's mantle radiogenic heat flow over time: contribution from 40K in yellow.
Atomic Weight Of K
The radioactive decay of 40K in the Earth's mantle ranks third, after 232Th and 238U, as the source of radiogenic heat. The core also likely contains radiogenic sources, although how much is uncertain. It has been proposed that significant core radioactivity (1–2 TW) may be caused by high levels of U, Th, and K.[3][4]
Potassium-40 is the largest source of natural radioactivity in animals including humans. A 70 kg human body contains about 140 grams of potassium, hence about 0.000117 × 140 = 0.0164 grams of 40K; whose decay produces about 4,300 disintegrations per second (becquerel) continuously throughout the life of the body.[5][6]
Banana equivalent dose[edit]
Potassium-40 is famous for its usage in the Banana equivalent dose, an informal unit of measurement, primarily used in generalized educational settings, to compare radioactive dosages to the amount received by consuming one banana. The radioactive dosage from consuming one banana is generally agreed to be 10−7 Sievert, or 0.1 microsievert which is 1% of the average American's daily radioactive intake.[7]
See also[edit]
Notes[edit]
K Ka Atomic Number
- ^This photon would be called an x-ray if emitted from an electron. In nuclear physics, it is common to name photons according to their origin rather than their energy, high energy photons produced by electrical transitions are called 'x-rays' while those emitted from atomic nuclei are called 'gamma rays' irrespective of their energy.
- ^Engelkemeir, D. W.; Flynn, K. F.; Glendenin, L. E. (1962). 'Positron Emission in the Decay of K40'. Physical Review. 126 (5): 1818. Bibcode:1962PhRv..126.1818E. doi:10.1103/PhysRev.126.1818.
- ^Wohlers, A.; Wood, B. J. (2015). 'A Mercury-like component of early Earth yields uranium in the core and high mantle 142Nd'. Nature. 520 (7547): 337–340. Bibcode:2015Natur.520..337W. doi:10.1038/nature14350. PMC4413371. PMID25877203.
- ^Murthy, V. Rama; Van Westrenen, Wim; Fei, Yingwei (2003). 'Experimental evidence that potassium is a substantial radioactive heat source in planetary cores'. Nature. 423 (6936): 163–5. Bibcode:2003Natur.423..163M. doi:10.1038/nature01560. PMID12736683.
- ^The number of radioactive decays per second in a given mass of 40K is the number of atoms in that mass, divided by the average lifetime of a 40K atom in seconds. The number of atoms in one gram of 40K is Avogadro's number 6.022×1023 (the number of atoms per mole) divided by the atomic weight of potassium-40 (39.96 grams per mole), which is about 0.1507×1023 per gram. As in any exponential decay, the average lifetime is the half-life divided by the natural logarithm of 2, or about 56.82×1015 seconds.
- ^Bin Samat, S.; Green, S.; Beddoe, A. H. (1997). 'The 40K activity of one gram of potassium'. Physics in Medicine and Biology. 42 (2): 407–13. Bibcode:1997PMB....42..407S. doi:10.1088/0031-9155/42/2/012. PMID9044422.
- ^https://www.radiation-dosimetry.org/what-is-banana-equivalent-dose-bed-definition/
References[edit]
External links[edit]
- Potassium-40 Section, Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas
![Number Number](/uploads/1/3/7/5/137521580/697599874.jpg)
See Full List On En.wikipedia.org
Lighter: potassium-39 | Potassium-40 is an isotope of potassium | Heavier: potassium-41 |
Decay product of: -- | Decay chain of potassium-40 | Decays to: argon-40, calcium-40, Stable |
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Potassium-40&oldid=1002799860'
Chemical properties of potassium - Health effects of potassium - Environmental effects of potassium
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Potassium The name is derived from the english word potash. The chemical symbol K comes from kalium, the Mediaeval Latin for potash, which may have derived from the arabic word qali, meaning alkali. Potassium is a soft, silvery-white metal, member of the alkali group of the periodic chart. Potassium is silvery when first cut but it oxidizes rapidly in air and tarnishes within minutes, so it is generally stored under oil or grease. It is light enough to float into water with which it reacts instantly to release hydrogen, which burns with a lilac flame. The chemistry of potassium is almost etirely that of the potassium ion, K+. Applications Most potassium (95 %) goes into fertilizers and the rest goes mainly into making potassium hydroxide (KOH), by the electrolysis of potassium chloride solution, and then converting this to potassium carbonate (K2CO3). Potassium carbonate goes into glass manufacture, expecially the glass used to make televisions, while potassium hydroxide is used to make liquid soaps and detergents. A little potassium chloride goes into pharmaceuticals, medical drips and saline injections. Other potassium salts are used in baking, photography and tanning leather, and to make iodize salts. In all cases it is the negative anion, not the potassium, which is the key to their use. Potassium in the environment Most potassium occurs in the Earth's crust as minerals, such as feldspars and clays. Potassium is leached from these by weathering, which explains why there is quite a lot of this element in the sea (0.75 g/liter). Minerals mined for their potassium are pinkish and sylvite, carnallite and alunite. The main mining area used to be Germany, which had a monopoly of potassium before the first World War. Today most potassium minerals come from Canada, USA and Chile. The world production of potassim ores is about 50 million tonnes, and reserves are vast (more than 10 billion tonnes). Potassium is a key plant element. Although it is soluble in water, little is lost from undisturbed soils because as it is released from dead plants and animal excrements, it quickly become strongly bound to clay particles, and it is retained ready to be readsorbed by the roots of other plants. Health effects of potassium
Environmental effects of potassiumTogether with nitrogen and phosphorous, potassium is one of the essential macrominerals for plant survival. Its presence is of great importance for soil health, plant growth and animal nutrition. Its primary function in the plant is its role in the maintenance of osmotic pressure and cell size, thereby influencing photosynthesis and energy production as well as stomatal opening and carbon dioxide supply, plant turgor and translocation of nutrients. As such, the element is required in relatively large proportions by the growing plant. The consequences of low potassium levels are apparent in a variety of symptoms: restricted growth, reduced flowering, lower yields and lower quality produce. High water soluble levels of potassium cause damage to germinating seedlings, inhibits the uptake of other minerals and reduces the quality of the crop. Check out our potassium in water page Back to the periodic table of elements |
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