Argon-39

Properties and data of the isotope ³⁹Ar.

Contents

General Data

Radioactive Decay

Parent Nuclides

NMR Data

Isotones und Isobares

Literature

Argon-39 is a radioisotope of the chemical element argon, which has 21 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 39.

A report on the discovery of the radioactive isotope appeared in 1950 [1]: According to this, Argon-39 was produced by irradiating potassium salts with neutrons according to the charge exchange reaction

³⁹K(n,p)³⁹Ar.

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

General data

Name of the isotope:Argon-39; Ar-39Symbol:³⁹Ar or 3918ArMass number A:39 (= number of nucleons)Atomic number Z:18 (= number of protons)Neutrons N:21Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):1.1666666666667 (= neutron-proton ratio)Neutron excess (N-Z):3Isotopic mass:38.964313(5) u (atomic weight of Argon-39)Nuclide mass:38.9544387 u (calculated nuclear mass without electrons)Mass excess:-33.24223 MeVMass defect:0.358500812 u (per nucleus)Nuclear binding energy:333.94135537 MeV (per nucleus)
8.56259886 MeV (average binding energy per nucleon)Separation energy:S_N = 6.599(5) MeV (first neutron)
S_P = 10.733(5) MeV (first proton)Half-life:268(8) aDecay constant λ:8.195887263724 × 10^-11 s^-1Specific activity α:1298862830902.9 Bq g^-1
35.104400835214 Ci g^-1Spin and parity:
(nuclear angular momentum)7/2-Magnetic dipole moment:μ(μ_N) = -1.590(15)Charge radius:3.4093(31) femtometer fmMirror nucleus:Scandium-39Year of discovery:1950

Radioactive Decay

Half-life T_½ = 268(8) a respectively 8.457256161 × 10⁹ seconds s.

Decay mode	Daughter	Probability	Decay energy	Details	γ energy (intensity)
β^-	³⁹K	100 %	0.565(5) MeV	β^-: 0.2188(21) MeV [100 %] ν: 0.347(3) MeV

Parent Nuclides

Direct parent isotope is: ³⁹Cl.

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+

NMR data

Nuclear magnetic properties and parameters of the NMR active Nuclide ³⁹Ar

Isotope:³⁹Ar-NMRQuantity:SpurenSpin:7/2-Nuclearmagnetic moment
μ/μ_N:-1.590(15)Gyromagnetic ratio γ:1.78 · 10⁷ rad T^-1 s^-1
2.83296 MHz T^-1Nuclear g-factor:g_l = -0.45428571428571Quadrupole moment Q:-0.12(3) barn (100 fm²)Line width parameter (factor):l = 19.59 fm⁴Resonance frequency:v₀ = 3.46 MHz at 1 TRelative Sensitivity:[related to ¹H = 1.000]:
0.01130 (H₀ = const.)
1.7080 (v₀ = const.)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 21) and isobaric (same nucleon number A = 39) with Argon-39. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 21	Isobar A = 39
9	³⁰F
10	³¹Ne
11	³²Na	³⁹Na
12	³³Mg	³⁹Mg
13	³⁴Al	³⁹Al
14	³⁵Si	³⁹Si
15	³⁶P	³⁹P
16	³⁷S	³⁹S
17	³⁸Cl	³⁹Cl
18	³⁹Ar	³⁹Ar
19	⁴⁰K	³⁹K
20	⁴¹Ca	³⁹Ca
21	⁴²Sc	³⁹Sc
22	⁴³Ti	³⁹Ti
23	⁴⁴V
24	⁴⁵Cr
25	⁴⁶Mn
26	⁴⁷Fe
27	⁴⁸Co
28	⁴⁹Ni