Potassium-41
Properties and data of the isotope 41K.
Potassium-41 is a stable, naturally occurring isotope of the chemical element potassium, which has 22 neutrons in its atomic nucleus in addition to the element-specific 19 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 41.
The discovery of potassium-41 during the investigation of positive anode rays using a Cavendish mass spectrograph was reported in 1921 [1].
See also: List of individual Potassium isotopes (and general data sources).
General data
Name of the isotope:Potassium-41; K-41Symbol:41K or 4119KMass number A:41 (= number of nucleons)Atomic number Z:19 (= number of protons)Neutrons N:22Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.1578947368421 (= neutron-proton ratio)Neutron excess (N-Z):3Isotopic mass:40.961825256(4) u (atomic weight of Potassium-41)Nuclide mass:40.9514024 u (calculated nuclear mass without electrons)Mass excess:-35.55954 MeVMass defect:0.377478504 u (per nucleus)Nuclear binding energy:351.6189616 MeV (per nucleus)
8.57607223 MeV (average binding energy per nucleon)Separation energy:SN = 10.09537(6) MeV (first neutron)
SP = 7.808620(4) MeV (first proton)Half-life:stableSpin and parity:
(nuclear angular momentum)3/2+Magnetic dipole moment:μ(μN) = +0.214872(5)Charge radius:3.4518(55) femtometer fmMirror nucleus:Titanium-41Year of discovery:1921
Parent Nuclides
Direct parent isotopes are: 41Ca, 41Ar.
Occurrence
Comparison of the natural Potassium isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):
| | Atomic Mass ma | Quantity | Half-life | Spin |
|---|
Potassium
Isotopic mixture | 39.0983 u | 100 % | | |
| Isotope 39K | 38.963706485(5) u | 93.2581(44) % | stable | 3/2+ |
| Isotope 40K | 39.96399817(6) u | 0.0117(1) % | 1.248(3) × 109 a | 4- |
| Isotope 41K | 40.961825256(4) u | 6.7302(44) % | stable | 3/2+ |
NMR data
Nuclear magnetic properties and parameters of the NMR active Nuclide 41K
Isotope:41K-NMRQuantity:6.7302(44) %Spin:3/2+Nuclearmagnetic moment
μ/μN:+0.214872(5)Gyromagnetic ratio γ:0.68606808 · 107 rad T-1 s-1
1.09191 MHz T-1Nuclear g-factor:gl = 0.143248Quadrupole moment Q:+0.734(7) barn (100 fm2)Line width parameter (factor):l = 7183.41 fm4Resonance frequency:v0 = 1.0919 MHz at 1 TRelative Sensitivity:[related to 1H = 1.000]:
0.00008 (H0 = const.)
0.1282 (v0 = const.)
0.00000568 (at natural abundance)
relative receptivity as compared to 13C:
0.0333 (at natural abundance)Reference compound:
(conditions)0.1 M Potassium chloride solution in Deuterium Oxide D2O.Frequency ratio:Ξ(41K) = 2.561305 % [based on the reference substance]
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 22) and isobaric (same nucleon number A = 41) with Potassium-41. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
| Z | Isotone N = 22 | Isobar A = 41 |
|---|
| 9 | 31F | |
| 10 | 32Ne | |
| 11 | 33Na | |
| 12 | 34Mg | |
| 13 | 35Al | 41Al |
| 14 | 36Si | 41Si |
| 15 | 37P | 41P |
| 16 | 38S | 41S |
| 17 | 39Cl | 41Cl |
| 18 | 40Ar | 41Ar |
| 19 | 41K | 41K |
| 20 | 42Ca | 41Ca |
| 21 | 43Sc | 41Sc |
| 22 | 44Ti | 41Ti |
| 23 | 45V | 41V |
| 24 | 46Cr | 41Cr |
| 25 | 47Mn | |
| 26 | 48Fe | |
| 27 | 49Co | |
| 28 | 50Ni | |
External data and identifiers
Literature and References
[1] - F. W. ASTON:
The Constitution of the Alkali Metals.
In: Nature, 107, 72, (1921), DOI 10.1038/107072b0.
Last update: 2026-01-07
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