Argon-38

Properties and data of the isotope ³⁸Ar.

Contents

Argon-38 is a naturally occurring, stable isotope of the chemical element argon, which has 20 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 38.

A report on the discovery of Argon-38 appeared in 1934 [P. Zeeman, J. de Gier: A new isotope of argon. Proc. Akad. Soc. Amsterdam 37 (1934) 3].

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

General data

Name of the isotope:Argon-38; Ar-38Symbol:³⁸Ar or 3818ArMass number A:38 (= number of nucleons)Atomic number Z:18 (= number of protons)Neutrons N:20Nucleon pairing (Z - N):even - evenNuclear ratio (N/Z ratio):1.1111111111111 (= neutron-proton ratio)Neutron excess (N-Z):2Isotopic mass:37.96273210(21) u (atomic weight of Argon-38)Nuclide mass:37.9528578 u (calculated nuclear mass without electrons)Mass excess:-34.71483 MeVMass defect:0.351416796 u (per nucleus)Nuclear binding energy:327.34263697 MeV (per nucleus)
8.61427992 MeV (average binding energy per nucleon)Separation energy:S_N = 11.83847(28) MeV (first neutron)
S_P = 10.24225(20) MeV (first proton)Half-life:stableSpin and parity:
(nuclear angular momentum)0+Charge radius:3.4028(19) femtometer fmMirror nucleus:Calcium-38Year of discovery:1934

Parent Nuclides

Direct parent isotopes are: ³⁸K, ³⁸Cl.

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 = 20) and isobaric (same nucleon number A = 38) with Argon-38. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 20	Isobar A = 38
8	²⁸O
9	²⁹F
10	³⁰Ne
11	³¹Na	³⁸Na
12	³²Mg	³⁸Mg
13	³³Al	³⁸Al
14	³⁴Si	³⁸Si
15	³⁵P	³⁸P
16	³⁶S	³⁸S
17	³⁷Cl	³⁸Cl
18	³⁸Ar	³⁸Ar
19	³⁹K	³⁸K
20	⁴⁰Ca	³⁸Ca
21	⁴¹Sc	³⁸Sc
22	⁴²Ti	³⁸Ti
23	⁴³V
24	⁴⁴Cr
25	⁴⁵Mn
26	⁴⁶Fe
27	⁴⁷Co
28	⁴⁸Ni