Potassium-55

Properties and data of the isotope ⁵⁵K.

Contents

Potassium-55 is a radioisotope of the chemical element potassium, which has 36 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 55. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ⁵⁵K is exclusively for academic purposes.

The discovery of the neutron-rich K nuclide was first reported in 2009; potassium-55, along with other isotopes, was produced and observed by irradiating a beryllium-9 template with germanium-76 ions (132 MeV/u) [1].

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

General data

Name of the isotope:Potassium-55; K-55Symbol:⁵⁵K or 5519KMass number A:55 (= number of nucleons)Atomic number Z:19 (= number of protons)Neutrons N:36Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.8947368421053 (= neutron-proton ratio)Neutron excess (N-Z):17Isotopic mass:55.00051(54) u (atomic weight of Potassium-55)Nuclide mass:54.9900872 u (calculated nuclear mass without electrons)Mass excess:0.47506 MeVMass defect:0.460102584 u (per nucleus)Nuclear binding energy:428.58279638 MeV (per nucleus)
7.79241448 MeV (average binding energy per nucleon)Separation energy:S_N = 2.451(640) MeV (first neutron)
S_P = 19.379(944) MeV (first proton)Half-life:> 360 nsDecay constant λ:1925408.8348887 s^-1Specific activity α:2.108196948484 × 10⁺²⁸ Bq g^-1
5.697829590499 × 10⁺¹⁷ Ci g^-1Spin and parity:
(nuclear angular momentum)(3/2+)Year of discovery:2009

Radioactive Decay

Half-life T_½ = > 360 ns respectively 3.6 × 10^-7 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	⁵⁵Ca	100 %	19.12(53) MeV
β^-, xn ?

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 36) and isobaric (same nucleon number A = 55) with Potassium-55. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 36	Isobar A = 55
18	⁵⁴Ar
19	⁵⁵K	⁵⁵K
20	⁵⁶Ca	⁵⁵Ca
21	⁵⁷Sc	⁵⁵Sc
22	⁵⁸Ti	⁵⁵Ti
23	⁵⁹V	⁵⁵V
24	⁶⁰Cr	⁵⁵Cr
25	⁶¹Mn	⁵⁵Mn
26	⁶²Fe	⁵⁵Fe
27	⁶³Co	⁵⁵Co
28	⁶⁴Ni	⁵⁵Ni
29	⁶⁵Cu	⁵⁵Cu
30	⁶⁶Zn	⁵⁵Zn
31	⁶⁷Ga
32	⁶⁸Ge
33	⁶⁹As
34	⁷⁰Se
35	⁷¹Br
36	⁷²Kr
37	⁷³Rb
38	⁷⁴Sr