Actinium-227 is the radioisotope of the element actinium, whose atomic nucleus has 138 neutrons in addition to the element-specific 89 protons, from which the mass number 227 Ac results.
Because of its short half-life of around 21.8 years, actinium is a rare, radioactive element whose natural occurrences usually refer to this isotope. Likewise, the mass number of actinium-227 is given as [227] in scientific tables and in the periodic table, since it is the most stable Ac nuclide.
227Ac occurs in nature mainly as an intermediate product in the decay series of uranium and thorium. In practical terms, it can be used as a radiation source for industrial or medical applications, for example. However, the quantities required for this are produced artificially: either in breeder reactors or in a cyclotron.
See also: List of individual Actinium isotopes (and general data sources).
General data
Name of the isotope:Actinium-227; Ac-227Other names:ActiniumSymbol:227Ac or 22789AcMass number A:227 (= number of nucleons)Atomic number Z:89 (= number of protons)Neutrons N:138Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.5505617977528 (= neutron-proton ratio)Neutron excess (N-Z):49Isotopic mass:227.0277507(21) u (atomic weight of Actinium-227)Nuclide mass:226.9789333 u (calculated nuclear mass without electrons)Mass excess:25.84961 MeVMass defect:1.864435556 u (per nucleus)Nuclear binding energy:1736.7105338 MeV (per nucleus) 7.6507072 MeV (average binding energy per nucleon)Separation energy:SN = 6.531(3) MeV (first neutron) SP = 5.1072(22) MeV (first proton)Cross section:σ(n.γ) = 880(70) barn (thermal neutron capture cross-section)Half-life:21.772(3) yearsDecay constant λ:1.009533019919 × 10-9 s-1Specific activity α:2677888464770.6 Bq g-1 72.375363912719 Ci g-1Spin and parity: (nuclear angular momentum)3/2-Magnetic dipole moment:μ(μN) = + 1.1(1)Year of discovery:1902
Radioactive Decay
Half-life T½ = 21.772(3) years respectively 6.86601792 × 108 seconds s.
Comparison of the natural Actinium isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):
Atomic Mass ma
Quantity
Half-life
Spin
Actinium Isotopic mixture
227.027752408 u
100 %
Isotope 227Ac
227.0277507(21) u
100 %
21.772(3) years
3/2-
NMR data
Nuclear magnetic properties and parameters of the NMR active Nuclide227Ac
Isotope:227Ac-NMRQuantity:100 %Spin:3/2-Nuclearmagnetic moment μ/μN:+ 1.1(1)Gyromagnetic ratio γ:3.5 · 107 rad T-1 s-1 5.57042 MHz T-1Nuclear g-factor:gl = 0.73333333333333Quadrupole moment Q:+1.74(10) barn (100 fm2)Line width parameter (factor):l = 40368 fm4Resonance frequency:v0 = 5.6 MHz at 1 TRelative Sensitivity:[related to 1H = 1.000]: 0.01131 (H0 = const.) 0.6565 (v0 = const.)
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 138) and isobaric (same nucleon number A = 227) with Actinium-227. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
