Argon-36

Properties and data of the isotope ³⁶Ar.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Argon-36 is a naturally occurring, stable isotope of the chemical element argon, which has 18 neutrons in its atomic nucleus in addition to the element-specific 18 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 36.

The first mass spectroscopic detection and thus the discovery of Argon-36 was reported in 1920 [1].

See also: List of individual Argon isotopes (and general data sources).

General data

Name of the isotope:Argon-36; Ar-36Symbol:³⁶Ar or 3618ArMass number A:36 (= number of nucleons)Atomic number Z:18 (= number of protons)Neutrons N:18Nucleon pairing (Z - N):even - evenNuclear ratio (N/Z ratio):1 (= neutron-proton ratio)Neutron excess (N-Z):0Isotopic mass:35.967545106(29) u (atomic weight of Argon-36)Nuclide mass:35.9576708 u (calculated nuclear mass without electrons)Mass excess:-30.23154 MeVMass defect:0.329273958 u (per nucleus)Nuclear binding energy:306.71671623 MeV (per nucleus)
8.51990878 MeV (average binding energy per nucleon)Separation energy:S_N = 15.2556(7) MeV (first neutron)
S_P = 8.50698(4) MeV (first proton)Half-life:stableSpin and parity:
(nuclear angular momentum)0+Charge radius:3.3905(23) femtometer fmYear of discovery:1920

Radioactive Decay

Argon is a stable isotope! Theoretically, the nuclide could undergo neutrinoless double beta decay (0νββ); however, this has not yet been experimentally proven.

Half-life T_½ = stable.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
0νββ ?

Parent Nuclides

Direct parent isotopes are: ³⁷Ca, ³⁶K, ³⁶Cl, ⁴⁰Sc.

Occurrence

Comparison of the natural Argon isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Argon Isotopic mixture	39.88 u	100 %
Isotope ³⁶Ar	35.967545106(29) u	0.3336(210) %	stable	0+
Isotope ³⁸Ar	37.96273210(21) u	0.0629(70) %	stable	0+
Isotope ³⁹Ar	38.964313(5) u	[trace]	268(8) a	7/2-
Isotope ⁴⁰Ar	39.962383120(23) u	99.6035(250) %	stable	0+
Isotope ⁴²Ar	41.963046(6) u	[trace]	32.9(11) a	0+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 18) and isobaric (same nucleon number A = 36) with Argon-36. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 18	Isobar A = 36
7	²⁵N
8	²⁶O
9	²⁷F
10	²⁸Ne
11	²⁹Na	³⁶Na
12	³⁰Mg	³⁶Mg
13	³¹Al	³⁶Al
14	³²Si	³⁶Si
15	³³P	³⁶P
16	³⁴S	³⁶S
17	³⁵Cl	³⁶Cl
18	³⁶Ar	³⁶Ar
19	³⁷K	³⁶K
20	³⁸Ca	³⁶Ca
21	³⁹Sc	³⁶Sc
22	⁴⁰Ti
23	⁴¹V
24	⁴²Cr
25	⁴³Mn