Argon-33
Properties and data of the isotope 33Ar.
Argon-33 is a radioisotope of the chemical element argon, which has 15 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 33.
See also: List of individual Argon isotopes (and general data sources).
General data
Name of the isotope:Argon-33; Ar-33Symbol:33Ar or 3318ArMass number A:33 (= number of nucleons)Atomic number Z:18 (= number of protons)Neutrons N:15Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):0.83333333333333 (= neutron-proton ratio)Neutron excess (N-Z):-3Isotopic mass:32.9899255(4) u (atomic weight of Argon-33)Nuclide mass:32.9800512 u (calculated nuclear mass without electrons)Mass excess:-9.38434 MeVMass defect:0.280898816 u (per nucleus)Nuclear binding energy:261.65556171 MeV (per nucleus)
7.92895642 MeV (average binding energy per nucleon)Separation energy:SN = 15.2553(18) MeV (first neutron)
SP = 3.3386(7) MeV (first proton)Half-life:174.3(11) msDecay constant λ:3.9767480238666 s-1Specific activity α:7.483917738812 × 10+22 Bq g-1
2022680469949.3 Ci g-1Spin and parity:
(nuclear angular momentum)1/2+Magnetic dipole moment:μ(μN) = -0.723(6)Nuclear g-factor:gl = -1.446Charge radius:3.3438(57) femtometer fmMirror nucleus:Phosphorus-33Year of discovery:1964
Radioactive Decay
Half-life T½ = 174.3(11) ms respectively 1.743 × 10-1 seconds s.
Decay
mode | Daughter | Probability | Decay energy | γ energy
(intensity) |
|---|
| EC/β+ | 33Cl | 61.3(10) % | 11.6190(6) MeV | |
| β+ p | 32S | 38.7(10) % | 9.343 MeV | |
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 15) and isobaric (same nucleon number A = 33) with Argon-33. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
| Z | Isotone N = 15 | Isobar A = 33 |
|---|
| 5 | 20B | |
| 6 | 21C | |
| 7 | 22N | |
| 8 | 23O | |
| 9 | 24F | |
| 10 | 25Ne | 33Ne |
| 11 | 26Na | 33Na |
| 12 | 27Mg | 33Mg |
| 13 | 28Al | 33Al |
| 14 | 29Si | 33Si |
| 15 | 30P | 33P |
| 16 | 31S | 33S |
| 17 | 32Cl | 33Cl |
| 18 | 33Ar | 33Ar |
| 19 | 34K | 33K |
| 20 | 35Ca | |
| 21 | 36Sc | |
External data and identifiers
Literature and References
[1] - P. L. Reeder, A. M. Poskanzer, R. A. Esterlund:
New Delayed-Proton Emitters: Ti41, Ca37, and Ar33.
In: Physical Review Letters, 13, 797, (1964), DOI 10.1103/PhysRevLett.13.767.
[2] - J. C. Hardy, R. I. Verrall:
Delayed Protons Following the Decay of Argon-33.
In: Canadian Journal of Physics, 43, 3, (1965), DOI 10.1139/p65-038.
Last update: 2026-01-04
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