Argon-42

Properties and data of the isotope ⁴²Ar.

Content

General data

Name of the isotope:Argon-42; Ar-42Symbol:⁴²Ar or 4218ArMass number A:42 (= number of nucleons)Atomic number Z:18 (= number of protons)Neutrons N:24Isotopic mass:41.963046(6) u (atomic weight of Argon-42)Nuclide mass:41.9531717 u (calculated nuclear mass without electrons)Mass excess:-34.42243 MeVMass defect:0.38576256 u (per nucleus)Nuclear binding energy:359.33551006 MeV (per nucleus)
8.55560738 MeV (average binding energy per nucleon)Separation energy:S_N = 9.426(6) MeV (first neutron)
S_P = 14.40(7) MeV (first proton)Half-life:32.9(11) aDecay constant λ:6.680936680095 × 10^-10 s^-1Specific activity α:9813058966794 Bq g^-1
265.21780991335 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Charge radius:3.4414(41) femtometer fmMirror nucleus:Chromium-42Year of discovery:1952

Radioactive Decay

Half-life T_½ = 32.9(11) a respectively 1.0375 × 10⁹ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	⁴²K	100 %	0.599(6) MeV

Parent Nuclides

Direct parent isotope is: ⁴²Cl.

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	35.9675451(2) u	0.3336(210) %	stable	0+
Isotope ³⁸Ar	37.962732(2) u	0.0629(70) %	stable	0+
Isotope ³⁹Ar	38.964313(5) u	[trace]	268(8) a	7/2-
Isotope ⁴⁰Ar	39.96238312(2) 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 = 24) and isobaric (same nucleon number A = 42) with Argon-42. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 24	Isobar A = 42
10	³⁴Ne
11	³⁵Na
12	³⁶Mg
13	³⁷Al	⁴²Al
14	³⁸Si	⁴²Si
15	³⁹P	⁴²P
16	⁴⁰S	⁴²S
17	⁴¹Cl	⁴²Cl
18	⁴²Ar	⁴²Ar
19	⁴³K	⁴²K
20	⁴⁴Ca	⁴²Ca
21	⁴⁵Sc	⁴²Sc
22	⁴⁶Ti	⁴²Ti
23	⁴⁷V	⁴²V
24	⁴⁸Cr	⁴²Cr
25	⁴⁹Mn	⁴²Mn
26	⁵⁰Fe
27	⁵¹Co
28	⁵²Ni
29	⁵³Cu
30	⁵⁴Zn