Nuclides with atomic number of 18 but with different mass numbers
Argon (18 Ar) has 26 known
isotopes , from 29 Ar to 54 Ar and 1
isomer (32m Ar), of which three are
stable (36 Ar, 38 Ar, and 40 Ar). On the Earth, 40 Ar makes up 99.6% of natural argon. The longest-lived radioactive isotopes are 39 Ar with a half-life of 268 years, 42 Ar with a half-life of 32.9 years, and 37 Ar with a half-life of 35.04 days. All other isotopes have half-lives of less than two hours, and most less than one minute. The least stable is 29 Ar with a half-life of approximately 4× 10−20 seconds.
[4]
The naturally occurring
40 K , with a
half-life of 1.248× 10 9 years, decays to stable 40 Ar by
electron capture (10.72%) and by
positron emission (0.001%), and also transforms to stable 40 Ca via
beta decay (89.28%). These properties and ratios are used to determine the age of
rocks through
potassium–argon dating .
[5]
Despite the trapping of 40 Ar in many rocks, it can be released by melting, grinding, and diffusion. Almost all of the argon in the Earth's atmosphere is the product of 40 K decay, since 99.6% of Earth atmospheric argon is 40 Ar, whereas in the Sun and presumably in primordial star-forming clouds, argon consists of < 15% 38 Ar and mostly (85%) 36 Ar. Similarly, the ratio of the three isotopes 36 Ar:38 Ar:40 Ar in the atmospheres of the
outer planets is measured to be 8400:1600:1.
[6]
In the Earth's
atmosphere , radioactive 39 Ar (half-life 268(8) years) is made by
cosmic ray activity, primarily from 40 Ar. In the subsurface environment, it is also produced through
neutron capture by 39 K or
alpha emission by
calcium . The content of 39 Ar in natural argon is measured to be of (8.0±0.6)×10−16 g/g, or (1.01±0.08) Bq/kg of 36, 38, 40 Ar.
[7] The content of 42 Ar (half-life 33 years) in the Earth's atmosphere is lower than 6×10−21 parts per part of 36, 38, 40 Ar.
[8] Many endeavors require argon depleted in the
cosmogenic isotopes , known as depleted argon.
[9] Lighter radioactive isotopes can decay to different elements (usually
chlorine ) while heavier ones decay to
potassium .
36 Ar, in the form of
argon hydride , was detected in the
Crab Nebula
supernova remnant during 2013.
[10]
[11] This was the first time a
noble molecule was detected in
outer space .
[10]
[11]
Radioactive 37 Ar is a synthetic radionuclide that is created from the
neutron capture by 40 Ca followed by an
alpha particle emission as a result of subsurface
nuclear explosions . It has a half-life of 35 days.
[5]
List of isotopes
Nuclide
[12]
[n 1]
Z
N
Isotopic mass (
Da )
[13]
[n 2]
[n 3]
Half-life
Decay mode
[n 4]
Daughter isotope
[n 5]
Spin and
parity
[n 6]
[n 7]
Natural abundance (mole fraction)
Excitation energy
Normal proportion
Range of variation
29 Ar
[4]
18
11
~40 zs
2p
27 S
30 Ar
18
12
30.02247(22)
<10 ps
2p
28 S
0+
31 Ar
18
13
31.01216(22)#
15.1(3) ms
β+ , p (68.3%)
30 S
5/2+
β+ (22.63%)
31 Cl
β+ , 2p (9.0%)
29 P
β+ , 3p (0.07%)
28 Si
32 Ar
18
14
31.9976378(19)
98(2) ms
β+ (64.42%)
32 Cl
0+
β+ , p (35.58%)
31 S
32m Ar
5600(100) keV
unknown
5−#
33 Ar
18
15
32.9899255(4)
173.0(20) ms
β+ (61.3%)
33 Cl
1/2+
β+ , p (38.7%)
32 S
34 Ar
18
16
33.98027009(8)
843.8(4) ms
β+
34 Cl
0+
35 Ar
18
17
34.9752577(7)
1.7756(10) s
β+
35 Cl
3/2+
36 Ar
18
18
35.967545105(29)
Observationally Stable
[n 8]
0+
0.003336(4)
37 Ar
18
19
36.96677631(22)
35.011(19) d
EC
37 Cl
3/2+
Trace
[n 9]
38 Ar
18
20
37.96273210(21)
Stable
0+
0.000629(1)
39 Ar
[n 10]
18
21
38.964313(5)
268.2+3.1 −2.9 y
[14]
β−
39 K
7/2−
Trace
[n 9]
40 Ar
[n 11]
18
22
39.9623831238(24)
Stable
0+
0.996035(4)
[n 12]
41 Ar
18
23
40.9645006(4)
109.61(4) min
β−
41 K
7/2−
Trace
[n 9]
42 Ar
18
24
41.963046(6)
32.9(11) y
β−
42 K
0+
43 Ar
18
25
42.965636(6)
5.37(6) min
β−
43 K
5/2(−)
44 Ar
18
26
43.9649238(17)
11.87(5) min
β−
44 K
0+
45 Ar
18
27
44.9680397(6)
21.48(15) s
β−
45 K
(5/2,7/2)−
46 Ar
18
28
45.9680374(12)
8.4(6) s
β−
46 K
0+
47 Ar
18
29
46.9727681(12)
1.23(3) s
β− (99.8%)
47 K
(3/2−)
β− ,
n (0.2%)
46 K
48 Ar
18
30
47.97608(33)
415(15) ms
β−
48 K
0+
49 Ar
18
31
48.98155(43)#
236(8) ms
β−
49 K
3/2−#
50 Ar
18
32
49.98569(54)#
106(6) ms
β−
50 K
0+
51 Ar
18
33
50.99280(64)#
60# ms [>200 ns]
β−
51 K
3/2−#
52 Ar
18
34
51.99863(64)#
10# ms
β−
52 K
0+
53 Ar
18
35
53.00729(75)#
3# ms
β−
53 K
(5/2−)#
β− , n
52 K
54 Ar
[15]
18
36
β−
54 K
0+
This table header & footer:
^ m Ar – Excited
nuclear isomer .
^ ( ) – Uncertainty (1σ ) is given in concise form in parentheses after the corresponding last digits.
^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
^
Modes of decay:
^ Bold symbol as daughter – Daughter product is stable.
^ ( ) spin value – Indicates spin with weak assignment arguments.
^ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
^ Believed to undergo double electron capture to 36 S (lightest theoretically unstable nuclide for which no evidence of radioactivity has been observed)
^
a
b
c
Cosmogenic nuclide
^ Used in
argon–argon dating
^ Used in
argon–argon dating and
potassium–argon dating
^ Generated from 40 K in rocks. These ratios are terrestrial. Cosmic abundance is far less than 36 Ar.
See also
References
^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021).
"The NUBASE2020 evaluation of nuclear properties" (PDF) . Chinese Physics C . 45 (3): 030001.
doi :
10.1088/1674-1137/abddae .
^
"Standard Atomic Weights: Argon" .
CIAAW . 2017.
^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022).
"Standard atomic weights of the elements 2021 (IUPAC Technical Report)" . Pure and Applied Chemistry .
doi :
10.1515/pac-2019-0603 .
ISSN
1365-3075 .
^
a
b Mukha, I.; et al. (2018). "Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains". Physical Review C . 98 (6): 064308–1–064308–13.
arXiv :
1803.10951 .
Bibcode :
2018PhRvC..98f4308M .
doi :
10.1103/PhysRevC.98.064308 .
S2CID
119384311 .
^
a
b
"40 Ar/39 Ar dating and errors" . Archived from
the original on 9 May 2007. Retrieved 7 March 2007 .
^
Cameron, A.G.W. (1973). "Elemental and isotopic abundances of the volatile elements in the outer planets". Space Science Reviews . 14 (3–4): 392–400.
Bibcode :
1973SSRv...14..392C .
doi :
10.1007/BF00214750 .
S2CID
119861943 .
^
P. Benetti; et al. (2007). "Measurement of the specific activity of 39 Ar in natural argon".
Nuclear Instruments and Methods A . 574 (1): 83–88.
arXiv :
astro-ph/0603131 .
Bibcode :
2007NIMPA.574...83B .
doi :
10.1016/j.nima.2007.01.106 .
S2CID
17073444 .
^
V. D. Ashitkov; et al. (1998). "New experimental limit on the 42 Ar content in the Earth's atmosphere".
Nuclear Instruments and Methods A . 416 (1): 179–181.
Bibcode :
1998NIMPA.416..179A .
doi :
10.1016/S0168-9002(98)00740-2 .
^
H. O. Back; et al. (2012).
"Depleted Argon from Underground Sources" .
Physics Procedia . 37 : 1105–1112.
Bibcode :
2012PhPro..37.1105B .
doi :
10.1016/j.phpro.2012.04.099 .
^
a
b Quenqua, Douglas (13 December 2013).
"Noble Molecules Found in Space" .
The New York Times . Retrieved 13 December 2013 .
^
a
b
Barlow, M. J.; et al. (2013). "Detection of a Noble Gas Molecular Ion, 36 ArH+, in the Crab Nebula".
Science . 342 (6164): 1343–1345.
arXiv :
1312.4843 .
Bibcode :
2013Sci...342.1343B .
doi :
10.1126/science.1243582 .
PMID
24337290 .
S2CID
37578581 .
^ Half-life, decay mode, nuclear spin, and isotopic composition is sourced in:Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017).
"The NUBASE2016 evaluation of nuclear properties" (PDF) . Chinese Physics C . 41 (3): 030001.
Bibcode :
2017ChPhC..41c0001A .
doi :
10.1088/1674-1137/41/3/030001 .
^ Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (2017).
"The AME2016 atomic mass evaluation (II). Tables, graphs, and references" (PDF) . Chinese Physics C . 41 (3): 030003-1–030003-442.
doi :
10.1088/1674-1137/41/3/030003 .
^ Golovko, Victor V. (15 October 2023). "Application of the most frequent value method for 39 Ar half-life determination". The European Physical Journal C . 83 (10).
arXiv :
2310.06867 .
doi :
10.1140/epjc/s10052-023-12113-6 .
ISSN
1434-6052 .
^ Neufcourt, L.; Cao, Y.; Nazarewicz, W.; Olsen, E.; Viens, F. (2019). "Neutron drip line in the Ca region from Bayesian model averaging". Physical Review Letters . 122 (6): 062502–1–062502–6.
arXiv :
1901.07632 .
Bibcode :
2019PhRvL.122f2502N .
doi :
10.1103/PhysRevLett.122.062502 .
PMID
30822058 .
S2CID
73508148 .
External links
Group
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Period
Hydrogen and alkali metals
Alkaline earth metals
Pnictogens
Chalcogens
Halogens
Noble gases
①
1
2
②
3
4
5
6
7
8
9
10
③
11
12
13
14
15
16
17
18
④
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
⑤
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
⑥
55
56
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
⑦
87
88
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
⑧
119
120
57
58
59
60
61
62
63
64
65
66
67
68
69
70
89
90
91
92
93
94
95
96
97
98
99
100
101
102