Chlorine-40
Properties and data of the isotope 40Cl.
Chlorine-40 is a radioisotope of the chemical element chlorine, which has 23 neutrons in its atomic nucleus in addition to the element-specific 17 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 40. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of 40Cl is exclusively for academic purposes.
See also: List of individual Chlorine isotopes (and general data sources).
General data
Name of the isotope:Chlorine-40; Cl-40Symbol:40Cl or 4017ClMass number A:40 (= number of nucleons)Atomic number Z:17 (= number of protons)Neutrons N:23Nucleon pairing (Z - N):odd - oddNuclear ratio (N/Z ratio):1.3529411764706 (= neutron-proton ratio)Neutron excess (N-Z):6Isotopic mass:39.97042(3) u (atomic weight of Chlorine-40)Nuclide mass:39.9610943 u (calculated nuclear mass without electrons)Mass excess:-27.55359 MeVMass defect:0.361898612 u (per nucleus)Nuclear binding energy:337.10638569 MeV (per nucleus)
8.42765964 MeV (average binding energy per nucleon)Separation energy:SN = 5.829(32) MeV (first neutron)
SP = 11.684(5) MeV (first proton)Half-life:1.35(3) minDecay constant λ:0.00085573725995055 s-1Specific activity α:1.321377004748 × 10+19 Bq g-1
357128920.20224 Ci g-1Spin and parity:
(nuclear angular momentum)2-Mirror nucleus:Vanadium-40Year of discovery:1956
Radioactive Decay
Half-life T½ = 1.35(3) min (minutes) respectively 8.10 × 102 seconds s.
Decay
mode | Daughter | Probability | Decay energy | γ energy
(intensity) |
|---|
| β- | 40Ar | 100 % | 7.48(3) MeV | |
Parent Nuclides
Direct parent isotope is: 40S.
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 23) and isobaric (same nucleon number A = 40) with Chlorine-40. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
| Z | Isotone N = 23 | Isobar A = 40 |
|---|
| 10 | 33Ne | |
| 11 | 34Na | |
| 12 | 35Mg | 40Mg |
| 13 | 36Al | 40Al |
| 14 | 37Si | 40Si |
| 15 | 38P | 40P |
| 16 | 39S | 40S |
| 17 | 40Cl | 40Cl |
| 18 | 41Ar | 40Ar |
| 19 | 42K | 40K |
| 20 | 43Ca | 40Ca |
| 21 | 44Sc | 40Sc |
| 22 | 45Ti | 40Ti |
| 23 | 46V | 40V |
| 24 | 47Cr | |
| 25 | 48Mn | |
| 26 | 49Fe | |
| 27 | 50Co | |
| 28 | 51Ni | |
External data and identifiers
Literature and References
[1] - H. Morinaga:
Radioactive Isotopes Cl40 and Ga74.
In: Physical Review, 103, 504, (1956), DOI 10.1103/PhysRev.103.504.
Last update: 2026-01-02
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