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Isotopes of Argon

List, data and properties of all known isotopes of Argon.

Content
Atomic properties
Decay properties
NMR active nuclides
Radiation protection
References
Argon isotopes

An argon isotope is an atom that has exactly Z = 18 protons in the nucleus; the individual nuclides differ in the number of neutrons (N) and thus in the total number of nucleons A (= mass number = Z + < i>N). In the uncharged Ar isotope, the number of electrons is equal to the number of protons.

A total of 24 isotopes with the mass numbers 30 to 53 and one nuclear isomer are known.

 

Naturally Occurring Argon Isotopes

Five of these isotopes occur naturally: Argon-36, Argon-38 and Argon-40 have stable nuclides, with Argon-36 being the lightest known Ar isotope, which is theoretically considered unstable. However, no such observations have been made to date. In addition, traces of the radioisotopes argon-40 (potassium-argon dating) and argon-42 can be found on earth and in the atmosphere.

Atomic Mass maQuantityHalf-lifeSpin
Argon
Isotopic mixture		39,88 u100 %
Isotope 36Ar35,9675451(2) u0,3336(210) %stable0+
Isotope 38Ar37,962732(2) u0,0629(70) %stable0+
Isotope 39Ar38,964313(5) utraces268(8) a7/2-
Isotope 40Ar39,96238312(2) u99,6035(250) %stable0+
Isotope 42Ar41,963046(6) utraces32.9(11) a0+

 

The average atomic weight can vary due to fluctuations in the isotopic composition of natural argon.

 

Isotope Table: Argon

The two following tables list the most important data and properties of the Argon isotopes. Further information on the individual Argon isotopes is listed on separate pages and can be accessed via the link in column 1.

 

Atomic Properties

Isotope
Nuclide		ENAtomic Mass
[Nuclear Mass]
{Mass Excess}		Spin I
(h/2π)		Parent
123456
Argon-303018Ar1230.02247(22) u
[30.0125957 u]
{20.93067 MeV}		0+
Argon-313118Ar1331.01216(22) u
[31.0022857 u]
{11.32697 MeV}		5/2+
Argon-323218Ar1431.9976378(19) u
[31.9877635 u]
{-2.20038 MeV}		0+
Argon-333318Ar1532.9899255(4) u
[32.9800512 u]
{-9.38434 MeV}		1/2+
Argon-343418Ar1633.98027009(8) u
[33.9703958 u]
{-18.37829 MeV}		0+35Ca
Argon-353518Ar1734.9752577(7) u
[34.9653834 u]
{-23.0473 MeV}		3/2+36Ca
35K
Argon-363618Ar1835.9675451(2) u
[35.9576708 u]
{-30.23154 MeV}		0+37Ca
36K
36Cl
40Sc
Argon-373718Ar1936.96677631(22) u
[36.956902 u]
{-30.94767 MeV}		3/2+37K
Argon-383818Ar2037.962732(2) u
[37.9528577 u]
{-34.71492 MeV}		0+38K
38Cl
Argon-393918Ar2138.964313(5) u
[38.9544387 u]
{-33.24223 MeV}		7/2-39Cl
Argon-404018Ar2239.96238312(2) u
[39.9525088 u]
{-35.0399 MeV}		0+40Cl
40K
Argon-414118Ar2340.9645006(4) u
[40.9546263 u]
{-33.06748 MeV}		7/2-41Cl
Argon-424218Ar2441.963046(6) u
[41.9531717 u]
{-34.42243 MeV}		0+42Cl
Argon-434318Ar2542.965636(6) u
[42.9557617 u]
{-32.00986 MeV}		5/2(-)43Cl
Argon-444418Ar2643.9649238(17) u
[43.9550495 u]
{-32.67327 MeV}		0+44Cl
45Cl
Argon-454518Ar2744.9680397(6) u
[44.9581654 u]
{-29.77083 MeV}		5/2-,7/2-45Cl
46Cl
Argon-464618Ar2845.9680374(12) u
[45.9581631 u]
{-29.77297 MeV}		0+46Cl
Argon-474718Ar2946.9727681(12) u
[46.9628938 u]
{-25.36635 MeV}		(3/2)-
Argon-484818Ar3047.97608(33) u
[47.9662057 u]
{-22.28134 MeV}		0+
Argon-494918Ar3148.98155(43) u
[48.9716757 u]
{-17.18606 MeV}
Argon-505018Ar3249.98569(54) u
[49.9758157 u]
{-13.32968 MeV}		0+
Argon-515118Ar3350.99280(64) u
[50.9829257 u]
{-6.70676 MeV}		3/2-
Argon-525218Ar3451.99863(64) u
[51.9887557 u]
{-1.27615 MeV}		0+
Argon-535318Ar3553.00729(75) u
[52.9974157 u]
{6.79059 MeV}

 

Radioactive Decay Properties

IsotopeRadioactive DecayExtern
Half-lifeDecay ModeProbabilityEnergy
789101112
Ar-3010 ps2p 28S100 %AL
Ar-3114.4(6) msEC/β+ → 31Cl
β+, p 30S
β+, 2p 29P
β+, 3p 28Si
63(7) %
7.2(11) %
2.1(10) %		18.36(20) MeV


AL
Ar-3298(2) msEC/β+ → 32Cl
ε, p → 31S		64.42(22) %
35.58(22) %		11.13475 MeV
9.555 MeV		AL
Ar-33173.0(20) msEC/β+ → 33Cl
ε, p → 32S		61.3(10) %
38.7(10) %		11.61896 MeV
9.343 MeV		AL
Ar-34843.8(4) msEC/β+ → 34Cl100 %6.06264 MeVAL
Ar-351.7756(10) sEC/β+ → 35Cl100 %5.9662(7) MeVAL
Ar-36stableAL
Ar-3735.011(19) dEC → 37Cl100 %0.813873(213) MeVAL
Ar-38stableAL
Ar-39268(8) aβ- → 39K100 %0.565(5) MeVAL
Ar-40stableAL
Ar-41109.61(4) minβ- → 41K100 %2.4920(3) MeVAL
Ar-4232.9(11) aβ- → 42K100 %0.599(6) MeVAL
Ar-435.37(6) minβ- → 43K100 %4.566(5) MeVAL
Ar-4411.87(5) minβ- → 44K100 %3.1082(16) MeVAL
Ar-4521.48(15) sβ- → 45K100 %6.8448(7) MeVAL
Ar-468.4(6) sβ- → 46K100 %5.6410(13) MeVAL
Ar-471.23(3) sβ- → 47K
β-, n → 46K		> 99.8 %
< 0.2 %		10.3456(18) MeV
1.9763(13) MeV		AL
Ar-48475(40) msβ- → 48K100 %10.00(31) MeVAL
Ar-49170(50) msβ- → 49K
β-, n → 48K		35(20) %
65(20) %		12.42(40) MeV
7.02(40) MeV		AL
Ar-50106(6) msβ- → 50K
β-, n → 49K
β-, 2n → 48K		65 %
35(7) %
?		12.40(50) MeV
8.21(50) MeV
AL
Ar-51> 60 msβ- → 51K100 %15.83(60) MeVAL
Ar-52620 nsβ- → 52K
β-, n → 51K
β-, 2n → 50K		?
?
?		15.86(60) MeV
13.16(60) MeV
AL
Ar-53620 nsβ- → 53K
β-, n → 52K
β-, 2n → 51k		?
?
?		19.09(71) MeV
15.86(70) MeV
AL

 

Notes (related to the columns):

1 - name of the nuclide, isotope.
2 - E: isotope symbol with mass number (superscript; number of nucleons) and atomic number (subscript; number of protons).
3 - N: number of neutrons.
4 - relative atomic mass of the Argon isotope (isotopic mass including electrons) and the mass of the atomic nucleus in square brackets (nuclear mass, nuclide mass without electrons), each related to 12C = 12.00000 [2]. In addition, the mass excess is given in MeV.
5 - nuclear spin I, unit: h/2π.
6 - source nuclides: Possible, assumed or actual source nuclides (mother nuclides, parent nuclides). If applicable, the corresponding decay modes can be found in the data for the respective starting nuclide.

7 - isotope notation in short form.
8 - decay: half-live of the Argon isotope (a = years; ; d = days; h = hours; min = minutes; s = seconds).
9 - decay mode: type of decay into the respective daughter nuclides with n = neutron emission; p = proton emission; α = alpha decay; β- = beta minus decay with electron emission; EC = electron capture; β+ = positron emission; ε = β+ and/or EC; Iso = isomeric transition; CD = cluster decay; SF = spontaneous decay.
10 - decay probability in percent (%).
11 - decay energy; Particle energy related to decay type.
12 - other information and notes: AL = Adopted Levels (link to external data [1]).

Miscellaneous:

()- Numbers in brackets: uncertainty to represent the spread of the reported value.
~ - Theoretical values or systematic trends.
  - unlisted-: Nuclides that have already been mentioned in the literature but for some reason can no longer be found in the current nuclide tables because their discovery e.g. has not confirmed.

 

NMR active Argon nuclides

Nuclide
quantity 1)
spin		Nuclear
magnetic
moment
μ/μN		Gyromagnetic ratio
{Quadrupole moment}		Resonant
frequency
v0 bei 1 T		Relative
sensitivity
H0 = const.
v0 = const. 3)
37Ar
-
3/2+		+ 1,146(5)
{+ 7,6(9)}		5,8190,01276
0,6833
39Ar
Spuren
7/2-		- 1,590(15)1,78
{- 12(3)}		3,460,01130
1,7080

1) Quantity Percentage of natural occurrence.

2) Gyromagnetic ratio: 107 rad T-1 s-1
    Quadrupole moment: Q fm-2

3) Related to 1H = 1,000.

 

Radiation Protection

According to the Radiation Protection Ordinance (StrlSchV 2018, Germany), the following values (columns 1 to 7) apply to the handling of Argon radionuclides:

NuclideLimit ValueHASS limitSCDaughter NuclidesHalf-life
Ar-37108 Bq1000000 Bq/gUnbegrenzt (UL)35.0 d
Ar-3910000 Bq10000000 Bq/g30 TBq269.0 a
Ar-41109 Bq100 Bq/g0,05 TBq1.8 h

(HASS = High-Activity Sealed Radioactive Sources; SC = surface contamination)

 

Literature Sources and References

Properties of the Argon nucleides

[1] - NuDat: National Nuclear Data Center, Brookhaven National Laboratory, based on ENSDF and the Nuclear Wallet Cards.

[2] - G. Audi et. al.: The NUBASE evaluation of nuclear and decay properties. Nuclear Physics, (2003), DOI 10.1016/j.nuclphysa.2003.11.001.

[3] - Live Chart of Nuclides. Nuclear structure and decay data.

Argon: NMR properties - 37Ar-NMR, 39Ar-NMR

[4] - N. J. Stone: Table of nuclear magnetic dipole and electric quadrupole moments. Atomic Data and Nuclear Data Tables, (2005), DOI 10.1016/j.adt.2005.04.001.

[5] - Pekka Pyykkö: Year-2008 nuclear quadrupole moments. Molecular Physics, (2008), DOI 10.1080/00268970802018367.

[6] - Pekka Pyykkö: Year-2017 nuclear quadrupole moments. Molecular Physics, (2018), DOI 10.1080/00268976.2018.1426131.

[7] - N. J. Stone: Table of recommended nuclear magnetic dipole moments. IAEA, (2019).

More sources:

[8] - Isotopic abundances, atomic weights and isotopic masses: see respective keyword.

 

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