Actinium-227

Properties and data of the isotope ²²⁷Ac.

Contents

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.

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:138Isotopic 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:S_N = 6.531(3) MeV (first neutron)
S_P = 5.1072(22) MeV (first proton)Cross section:σ(n.γ) = 880(70) barn (thermal neutron capture cross-section)Half-life:21.772(3) aDecay constant λ:1.009533019919 × 10^-9 s^-1Specific activity α:2678215880490.3 Bq g^-1
72.384212986224 Ci g^-1Spin and parity:
(nuclear angular momentum)3/2-Magnetic dipole moment:μ(μ_N) = + 1.1(1)Year of discovery:1902

Radioactive Decay

Half-life T_½ = 21.772(3) a respectively 6.86601792 × 10⁸ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²²³Fr	1.3800(36) %	5.04227(14) MeV
β^-	²²⁷Th	98.6200(36) %	0.0448(8) MeV

Parent Nuclides

Direct parent isotopes are: ²³¹Pa, ²²⁷Ra.

Occurrence

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

	Atomic Mass m_a	Quantity	Half-life	Spin
Actinium Isotopic mixture	227.027752408 u	100 %
Isotope ²²⁷Ac	227.0277507(21) u	100 %	21.772(3) a	3/2-

NMR data

Nuclear magnetic properties of the NMR active Nuclide ²²⁷Ac

Isotope:²²⁷Ac-NMRQuantity:100 %Spin:3/2-Nuclearmagnetic moment
μ/μ_N:+ 1.1(1)Gyromagnetic ratio γ:3.5 · 10⁷ rad T^-1 s^-1Nuclear g-factor:g_l = 0.73333333333333Quadrupole moment Q:+ 1.7(2) barn (100 fm²)Resonance frequency:v₀ = 5.6 at 1 TRelative Sensitivity:0.01131 (H₀ = const.)
0.6565 (v₀ = const.)
[related to ¹H = 1.000]

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.

Z	Isotone N = 138	Isobar A = 227
82	²²⁰Pb
83	²²¹Bi
84	²²²Po	²²⁷Po
85	²²³At	²²⁷At
86	²²⁴Rn	²²⁷Rn
87	²²⁵Fr	²²⁷Fr
88	²²⁶Ra	²²⁷Ra
89	²²⁷Ac	²²⁷Ac
90	²²⁸Th	²²⁷Th
91	²²⁹Pa	²²⁷Pa
92	²³⁰U	²²⁷U
93	²³¹Np	²²⁷Np
94	²³²Pu
95	²³³Am
96	²³⁴Cm
97	²³⁵Bk