Chlorine-36

Properties and data of the isotope ³⁶Cl.

Contents

General Data

Radioactive Decay

Occurrence

Isotones und Isobares

Literature

Chlorine-36 is a radioisotope of the chemical element chlorine, which has 19 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 36.

The discovery of the radioactive isotope was reported in 1941; according to this report, chlorine-36 (radio-chlorine) was formed by the irradiation of chlorine-containing compounds with neutrons [1]:

³⁵Cl(n,γ)³⁶Cl.

Cl-36 is produced in the upper atmosphere by the interaction of Argon-36 with protons that reach Earth with cosmic rays (spallation ).

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

General data

Name of the isotope:Chlorine-36; Cl-36Symbol:³⁶Cl or 3617ClMass number A:36 (= number of nucleons)Atomic number Z:17 (= number of protons)Neutrons N:19Nucleon pairing (Z - N):odd - oddNuclear ratio (N/Z ratio):1.1176470588235 (= neutron-proton ratio)Neutron excess (N-Z):2Isotopic mass:35.96830682(4) u (atomic weight of Chlorine-36)Nuclide mass:35.9589811 u (calculated nuclear mass without electrons)Mass excess:-29.52201 MeVMass defect:0.329352128 u (per nucleus)Nuclear binding energy:306.78953112 MeV (per nucleus)
8.52193142 MeV (average binding energy per nucleon)Separation energy:S_N = 8.57979(5) MeV (first neutron)
S_P = 7.964769(26) MeV (first proton)Half-life:3.013(15) × 10⁵ aDecay constant λ:7.294906222054 × 10^-14 s^-1Specific activity α:1255170080.8354 Bq g^-1
0.033923515698254 Ci g^-1Spin and parity:
(nuclear angular momentum)2+Magnetic dipole moment:μ(μ_N) = +1.28547(5)Quadrupole moment Q:- 0.0180(4) barn (100 fm²)Nuclear g-factor:g_l = 0.642735Mirror nucleus:Potassium-36Year of discovery:1941

Radioactive Decay

Half-life T_½ = 3.013(15) × 10⁵ a respectively 9.501797 × 10¹² seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EC/β⁺	³⁶S	1.9(1) %	1.14213(19) MeV
β^-	³⁶Ar	98.1(1) %	0.70953(4) MeV

Occurrence

Chlorine-36 is a radioisotope of the chemical element chlorine, which also occurs in nature, but only in extremely small amounts. The ratio to the other natural Cl isotopes is about 9 × 10^-13 : 1.

Comparison of the natural Chlorine isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Chlorine Isotopic mixture	35.45 u	100 %
Isotope ³⁵Cl	34.9688527(3) u	75.80(17) % [75.5 - 76.1 %]	stable	3/2+
Isotope ³⁶Cl	35.96830682(4) u	[trace]	3.013(15) × 10⁵ a	2+
Isotope ³⁷Cl	36.96590257(6) u	24.2 % [23.9 - 24.5 %]	stable	3/2+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 19) and isobaric (same nucleon number A = 36) with Chlorine-36. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

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

External data and identifiers

Adopted Levels, Gammas:NuDat 36Cl

Literature and References

[1] - David C. Grahame, Harold J. Walke:
Preparation and Properties of Long-Lived Radio-Chlorine.
In: Physical Review, 60, 909, (1941), DOI 10.1103/PhysRev.60.909.

[2] - Niklas Kappelt et al.:
Ice core dating with the ³⁶Cl/¹⁰Be ratio.
In: Quaternary Science Reviews, 335, 109254, (2025), DOI 10.1016/j.quascirev.2025.109254.