Potassium-40

Properties and data of the isotope ⁴⁰K.

Content

General Data

Radioactive Decay

NMR Data

Radiation Protection

Isotones und Isobares

Literature

General data

Name of the isotope:Potassium-40; K-40Symbol:⁴⁰KMass number A:40Atomic number Z:19 (= number of protons)Neutrons N:21Isotopic mass:39.9639982(4) u (atomic weight of Potassium-40)Nuclide mass:39.9535754 u (calculated nuclear mass without electrons)Mass excess:-33.53546 MeVMass defect:0.366640644 u (per nucleus)Nuclear binding energy:341.52356004 MeV (per nucleus)
8.538089 MeV (average binding energy per nucleon)Separation energy:S_N = 7.79962(6) MeV (first neutron)
S_P = 7.582(5) MeV (first proton)Half-life:1.248(3) × 10⁹ aDecay constant λ:1.761182124173 × 10^-17 s^-1Spin and parity:4-Charge radius:3.4381(28) femtometer fmYear of discovery:1935

Radioactive Decay

Half-life T_½ = 1.248(3) × 10⁹ a respectively 3.9356928 × 10¹⁶ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	⁴⁰Ca	89,28(11) %	1,31089(6) MeV
EE/β⁺	⁴⁰Ar	10,72(11) %	1,50440(6) MeV	1,460820(5) MeV 10,66(17) %

Occurrence

Comparison of the natural Kalium isotopes including isotopic abundance (proportion of the isotope mixture):

	Atomic Mass m_a	Quantity	Half-life	Spin
Kalium Isotopic mixture	39,0983 u	100 %
Isotope ³⁹K	38,96370649(3) u	93,2581(44) %	stable	3/2+
Isotope ⁴⁰K	39,9639982(4) u	0,0117(1) %	1.248(3) × 10⁹ a	4-
Isotope ⁴¹K	40,96182526(3) u	6,7302(44) %	stable	3/2+

NMR data

⁴⁰K belongs to the NMR active Nuclides.

Isotope:⁴⁰K-NMRQuantity:0,0117(1) %Spin:4-Nuclearmagnetic moment
μ/μ_N:-1,29797(3)Quadrupole moment
Q fm^-2:-7,50(8)Resonance frequency
v₀ at 1 T:2,4737Relative Sensitivity:0,00523 (H₀ = const.)
1,5493 (v₀ = const.)
[related to ¹H = 1,000]

Radiation Protection

Kaliumverbindungen und -präparate sind in Natur, Technik und Alltag allgegenwärtig vorhanden und gelten trotz des Anteils an K-40 nicht als radioaktive Gefahrstoffe; dazu ist die davon ausgehende Strahlung zu schwach.

Mit ⁴⁰K angereicherte Substanzen haben praktisch und technisch keinerlei Bedeutung; K-40 zählt zu den radioaktiven Substanzen, bei denen auch hohe Aktivitäten nicht zu einer Einstufung als hochradioaktive Strahlenquelle führen.

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
^40mK	1643,638(11) keV	0,336(13) μs	0+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 21) and isobaric (same nucleon number A = 40) with Potassium-40. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 21	Isobar A = 40
9	³⁰F
10	³¹Ne
11	³²Na
12	³³Mg	⁴⁰Mg
13	³⁴Al	⁴⁰Al
14	³⁵Si	⁴⁰Si
15	³⁶P	⁴⁰P
16	³⁷S	⁴⁰S
17	³⁸Cl	⁴⁰Cl
18	³⁹Ar	⁴⁰Ar
19	⁴⁰K	⁴⁰K
20	⁴¹Ca	⁴⁰Ca
21	⁴²Sc	⁴⁰Sc
22	⁴³Ti	⁴⁰Ti
23	⁴⁴V	⁴⁰V
24	⁴⁵Cr
25	⁴⁶Mn
26	⁴⁷Fe
27	⁴⁸Co
28	⁴⁹Ni

External data and identifiers

CAS:13966-00-2InChI Key:ZLMJMSJWJFRBEC-OUBTZVSYSA-NInChI Code:[40K]PubChem:ID 6328542Adopted Levels, Gammas:NuDat 40K

Literature and References

[1] - H. Leutz, G. Schulz, H. Wenninger:
The decay of potassium-40.
In: Zeitschrift für Physik, (1965), DOI 10.1007/BF01387190.

[2] - A. Ažman, A. Moljk, J. Pahor:
Electron capture in potassium 40.
In: Zeitschrift für Physik A, (1968), DOI 10.1007/BF01379914.

[3] - W. Sahm, A. Schwenk:
³⁹K, ⁴⁰K and ⁴¹K Nuclear Magnetic Resonance Studies.
In: Zeitschrift für Naturforschung A, (2014), DOI 10.1515/zna-1974-1208.