404:
367:
388:, 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 K 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 K and Ar atoms contained in it.
27:
491:
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
505:
The number of radioactive decays per second in a given mass of K is the number of atoms in that mass, divided by the average lifetime of a K atom in seconds. The number of atoms in one gram of K is the
423:. 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.
395:, with less than 15% of Ar. It follows that most of the terrestrial argon derives from potassium-40 that decayed into argon-40, which eventually escaped to the atmosphere.
391:
The argon found in Earth's atmosphere is 99.6% Ar; whereas the argon in the Sun – and presumably in the primordial material that condensed into the planets – is mostly
426:
Potassium-40 is the largest source of natural radioactivity in animals including humans. A 70 kg human body contains about 140 g of potassium, hence about
662:
Murthy, V. Rama; Van
Westrenen, Wim; Fei, Yingwei (2003). "Experimental evidence that potassium is a substantial radioactive heat source in planetary cores".
446:, an informal unit of measurement, primarily used in general educational settings, to compare radioactive dosages to the amount received by consuming one
380:
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
944:
732:
804:
713:
752:
929:
346:. The radioactive decay of this particular isotope explains the large abundance of argon (nearly 1%) in the
934:
939:
836:
566:
Engelkemeir, D. W.; Flynn, K. F.; Glendenin, L. E. (1962). "Positron
Emission in the Decay of K".
151:
443:
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407:
The evolution of Earth's mantle radiogenic heat flow over time: contribution from K in yellow.
860:
468:
347:
268:
837:
Radiological and
Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas
454:, or 0.1 microsievert, which is 1% of the average American's daily radioactive intake.
761:
750:
Bin Samat, S.; Green, S.; Beddoe, A. H. (1997). "The K activity of one gram of potassium".
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8:
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605:"A Mercury-like component of early Earth yields uranium in the core and high mantle Nd"
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300:
200:
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450:. The radioactive dosage from consuming one banana is generally agreed to be 10
351:
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100:
93:
39:
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335:
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49:
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144:
59:
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of K; whose decay produces about 3850 to 4300 disintegrations per second (
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The radioactive decay of K in the Earth's mantle ranks third, after
906:
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733:"What is Potassium-40 – Characteristics – Half-life – Definition"
451:
381:
354:. Very rarely (0.001% of events), it decays to Ar by emitting a
447:
26:
488:
565:
398:
533:, the average lifetime is the half-life divided by the
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299:
of 1.25 billion years. It makes up about 0.012% (120
749:
303:) of the total amount of potassium found in nature.
805:"What is Banana Equivalent Dose – BED – Definition"
521:of potassium-40 (39.96 g/mol), which is about
434:) continuously throughout the life of the person.
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718:Harvard Natural Sciences Lecture Demonstrations
596:
442:Potassium-40 is famous for its usage in the
802:
602:
559:
330:. In about 10.72% of events, it decays to
310:. In about 89.28% of events, it decays to
25:
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361:
945:Radionuclides used in radiometric dating
402:
365:
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306:Potassium-40 undergoes three types of
399:Contribution to natural radioactivity
322:) with a maximum energy of 1.31
743:
826:Table of radioactive isotopes, K-40
350:, as well as prevalence of Ar over
13:
730:
14:
956:
831:The Lund/LBNL Nuclear Data Search
819:
603:Wohlers, A.; Wood, B. J. (2015).
803:Nick Connor (14 December 2019).
16:Radioactive isotope of potassium
753:Physics in Medicine and Biology
496:" irrespective of their energy.
487:This photon would be called an
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1:
552:
338:(EC), with the emission of a
384:forms – whether from molten
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774:10.1088/0031-9155/42/2/012
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273:Complete table of nuclides
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714:"Radioactive Human Body"
590:10.1103/PhysRev.126.1818
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428:140g × 0.0117% ≈ 16.4 mg
314:(Ca) with emission of a
54:potassium-40, 40K, K-40
835:Potassium-40 Section,
444:banana equivalent dose
438:Banana equivalent dose
408:
371:
362:Potassium–argon dating
930:Isotopes of potassium
529:per gram. As in any
469:Isotopes of potassium
406:
369:
342:and then a 1.460 MeV
269:Isotopes of potassium
464:Background radiation
358:(β) and a neutrino.
20:Potassium-40, K
857:Potassium-40 is an
809:Radiation Dosimetry
766:1997PMB....42..407S
737:Radiation Dosimetry
684:10.1038/nature01560
676:2003Natur.423..163M
631:10.1038/nature14350
623:2015Natur.520..337W
582:1962PhRv..126.1818E
419:, as the source of
289:radioactive isotope
21:
935:Element toxicology
409:
372:
348:Earth's atmosphere
19:
940:Positron emitters
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617:(7547): 337–340.
535:natural logarithm
531:exponential decay
508:Avogadro constant
308:radioactive decay
295:which has a long
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101:Natural abundance
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897:of potassium-40
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820:External links
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852:potassium-39
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370:Decay scheme
328:antineutrino
305:
284:
281:Potassium-40
280:
279:
234:Decay energy
139:Isotope mass
117:
94:Nuclide data
81:
64:
893:Decay chain
576:(5): 1818.
515:10 mol
376:K–Ar dating
223:Decay modes
924:Categories
911:calcium-40
553:References
494:gamma rays
312:calcium-40
229:Decay mode
201:Primordial
106:0.0117(1)%
870:Heavier:
865:potassium
848:Lighter:
790:250778838
432:becquerel
344:gamma ray
297:half-life
293:potassium
132:10 y
113:Half-life
913:, Stable
907:argon-40
692:12736683
649:25877203
545:seconds.
458:See also
356:positron
340:neutrino
334:(Ar) by
332:argon-40
320:electron
128:1.251(3)
77:Neutrons
861:isotope
782:9044422
762:Bibcode
700:4430068
672:Bibcode
640:4413371
619:Bibcode
578:Bibcode
452:sievert
382:mineral
326:and an
318:(β, an
287:) is a
250:1.31109
60:Protons
34:General
901:Decays
788:
780:
698:
690:
664:Nature
647:
637:
610:Nature
523:0.1507
448:banana
263:1.5049
213:Ca (β)
40:Symbol
786:S2CID
696:S2CID
539:56.82
511:6.022
489:x-ray
475:Notes
50:Names
903:to:
884:of:
778:PMID
688:PMID
645:PMID
415:and
386:rock
152:Spin
863:of
770:doi
680:doi
668:423
635:PMC
627:doi
615:520
586:doi
574:126
324:MeV
301:ppm
291:of
259:, γ
238:MeV
190:keV
187:523
185:341
173:keV
169:505
167:−33
121:1/2
926::
909:,
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613:.
607:.
584:.
572:.
543:10
527:10
413:Th
393:Ar
257:EC
145:Da
88:21
71:19
887:—
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682::
674::
651:.
629::
621::
592:.
588::
580::
541:×
525:×
513:×
492:"
417:U
285:K
283:(
246:β
240:)
236:(
156:4
130:×
123:)
118:t
116:(
84:)
82:N
80:(
67:)
65:Z
63:(
44:K
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