Actinium

Actinium (Ac)

Silvery radioactive metallic element, belongs to group 3 of the periodic table. The most stable isotope, Ac-227, has a half-life of 217 years. Ac-228 (half-life of 6.13 hours) also occurs in nature. There are 22 other artificial isotopes, all radioactive and having very short half-lives. Chemistry similar to lanthanumpy. Used as a source of alpha particles. Discovered by A. Debierne in 1899.
Atomic Number89
Atomic Weight227
Mass Number205
Group3
Period7
Blockd
Protons89 p+
Neutrons116 n0
Electrons89 e-
Actinium sample (31481701837).png Electron shell 089 Actinium.svg Animated Bohr Model of Ac (Actinium) Enhanced Bohr Model of Ac (Actinium) Bohr Model: Ac (Actinium) Orbital Diagram of Ac (Actinium)

Properties

Atomic Radius
195 pm
Molar Volume
22.54 cm³/mol
Covalent Radius
186 pm
Metallic Radius
Ionic Radius
112 pm
Crystal Radius
126 pm
Van der Waals Radius
247 pm
Density
Energy
Proton Affinity
Electron Affinity
Ionization Energy
5.380226 eV/particle
Heat of Vaporization
292.9 kJ/mol
Heat of Fusion
10.5 kJ/mol
Heat of Formation
406 kJ/mol
Electrons
Electron Shells2, 8, 18, 32, 18, 9, 2
Valence Electrons3
Electron Configuration[Rn] 6d1 7s2
Oxidation States2, 3
Electronegativity
1.1
Electrophilicity
0.8159546412794374 eV/particle
Phases
PhaseSolid
Gas Phase
Boiling Point
3,473.15 K
Melting Point
1,323.15 K
Critical Pressure
Critical Temperature
Triple Point
Visual
Color
Silver
Appearance
Refractive Index
Thermodynamic Properties
Thermal Conductivity
Thermal Expansion
Molar Heat Capacity
Specific Heat Capacity
Heat Capacity Ratio (Adiabatic Index)
Electrical Properties
Type
Electrical Conductivity
Electrical Resistivity
Superconducting Point
Magnetism
Type
Magnetic Susceptibility (Mass)
Magnetic Susceptibility (Molar)
Magnetic Susceptibility (Volume)
Magnetic Ordering
Curie Point
Neel Point
Structure
Crystal StructureFace Centered Cubic (FCC)
Lattice Constant
5.31 Å
Lattice Anglesπ/2, π/2, π/2
Mechanical Properties
Hardness
Bulk Modulus
Shear Modulus
Young Modulus
Poisson Ratio
Speed of Sound
Classification
CategoryActinides, Actinides
CAS GroupIIIA
IUPAC GroupIIIB
Glawe Number33
Mendeleev Number14
Pettifor Number48
Geochemical ClassU/Th decay series
Goldschmidt Classsynthetic
Other
Gas Basicity
Dipole Polarizability
203 ± 12 a₀
C6 Dispersion Coefficient
Allotropes
Neutron Cross Section
880
Neutron Mass Absorption
0.078
Quantum Numbers2D3/2
Space Group225 (Fm_3m)

Isotopes of Actinium

Stable Isotopes0
Unstable Isotopes33
Radioactive Isotopes33

205Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
205.015144152 ± 0.000063682 Da
Mass Number205
G-Factor
Half Life
80 ± 60 ms
Spin9/2
Quadrupole Moment
Discovery Year2014
Parity-

205Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

206Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
206.014476477 ± 0.000069874 Da
Mass Number206
G-Factor
Half Life
25 ± 7 ms
Spin3
Quadrupole Moment
Discovery Year1998
Parity+

206Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

207Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
207.011965967 ± 0.000060384 Da
Mass Number207
G-Factor
Half Life
31 ± 8 ms
Spin9/2
Quadrupole Moment
Discovery Year1994
Parity-

207Ac Decay Modes
Decay ModeIntensity
α (α emission)100%

208Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
208.011552251 ± 0.000069225 Da
Mass Number208
G-Factor
Half Life
97 ± 15 ms
Spin3
Quadrupole Moment
Discovery Year1994
Parity+

208Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

209Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
209.009495375 ± 0.000059953 Da
Mass Number209
G-Factor
Half Life
94 ± 10 ms
Spin9/2
Quadrupole Moment
Discovery Year1968
Parity-

209Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

210Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
210.009408625 ± 0.000066782 Da
Mass Number210
G-Factor
Half Life
350 ± 40 ms
Spin7
Quadrupole Moment
Discovery Year1968
Parity+

210Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

211Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
211.007668846 ± 0.000057706 Da
Mass Number211
G-Factor
Half Life
213 ± 25 ms
Spin9/2
Quadrupole Moment
Discovery Year1968
Parity-

211Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

212Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
212.007836442 ± 0.000023492 Da
Mass Number212
G-Factor
Half Life
895 ± 28 ms
Spin7
Quadrupole Moment
Discovery Year1968
Parity+

212Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

213Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
213.006592665 ± 0.000012522 Da
Mass Number213
G-Factor
Half Life
738 ± 16 ms
Spin9/2
Quadrupole Moment
Discovery Year1968
Parity-

213Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

214Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
214.0069064 ± 0.000014547 Da
Mass Number214
G-Factor
Half Life
8.2 ± 0.2 s
Spin5
Quadrupole Moment
Discovery Year1968
Parity+

214Ac Decay Modes
Decay ModeIntensity
α (α emission)93%
β+ (β+ decay; β+ = ϵ + e+)7%

215Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
215.006474061 ± 0.000013318 Da
Mass Number215
G-Factor
Half Life
171 ± 10 ms
Spin9/2
Quadrupole Moment
Discovery Year1968
Parity-

215Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)0.09%

216Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
216.008749101 ± 0.000009908 Da
Mass Number216
G-Factor
Half Life
440 ± 16 us
Spin1
Quadrupole Moment
Discovery Year1967
Parity-

216Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

217Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
217.009342325 ± 0.000012048 Da
Mass Number217
G-Factor
0.85111111111111 ± 0.011111111111111
Half Life
69 ± 4 ns
Spin9/2
Quadrupole Moment
Discovery Year1972
Parity-

217Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

218Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
218.01164886 ± 0.000061853 Da
Mass Number218
G-Factor
Half Life
1 ± 0.04 us
Spin1
Quadrupole Moment
Discovery Year1970
Parity-

218Ac Decay Modes
Decay ModeIntensity
α (α emission)100%

219Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
219.012420425 ± 0.000055263 Da
Mass Number219
G-Factor
Half Life
9.4 ± 1 us
Spin9/2
Quadrupole Moment
Discovery Year1970
Parity-

219Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

220Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
220.014754527 ± 0.000006579 Da
Mass Number220
G-Factor
Half Life
26.36 ± 0.19 ms
Spin3
Quadrupole Moment
Discovery Year1970
Parity-

220Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

221Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
221.015599721 ± 0.000061086 Da
Mass Number221
G-Factor
Half Life
52 ± 2 ms
Spin9/2
Quadrupole Moment
Discovery Year1968
Parity-

221Ac Decay Modes
Decay ModeIntensity
α (α emission)100%

222Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
222.017844232 ± 0.000005044 Da
Mass Number222
G-Factor
Half Life
5 ± 0.5 s
Spin1
Quadrupole Moment
Discovery Year1949
Parity-

222Ac Decay Modes
Decay ModeIntensity
α (α emission)99%
β+ (β+ decay; β+ = ϵ + e+)1%

223Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
223.019135982 ± 0.000007457 Da
Mass Number223
G-Factor
Half Life
2.1 ± 0.05 m
Spin5/2
Quadrupole Moment
Discovery Year1948
Parity-

223Ac Decay Modes
Decay ModeIntensity
α (α emission)99%
ϵ (electron capture)%

224Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
224.021722249 ± 0.000004389 Da
Mass Number224
G-Factor
0
Half Life
2.78 ± 0.16 h
Spin0
Quadrupole Moment
0
Discovery Year1948
Parity-

224Ac Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)90.5%
α (α emission)9.5%
β (β decay)%

225Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
225.023228601 ± 0.000005107 Da
Mass Number225
G-Factor
Half Life
9.919 ± 0.0021 d
Spin3/2
Quadrupole Moment
Discovery Year1947
Parity-

225Ac Decay Modes
Decay ModeIntensity
α (α emission)100%
14C5.3%

226Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
226.026096999 ± 0.000003327 Da
Mass Number226
G-Factor
Half Life
29.37 ± 0.12 h
Spin1
Quadrupole Moment
Discovery Year1950
Parity-

226Ac Decay Modes
Decay ModeIntensity
β (β decay)83%
ϵ (electron capture)17%
α (α emission)0.006%

227Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
227.027750594 ± 0.000002068 Da
Mass Number227
G-Factor
Half Life
21.772 ± 0.003 y
Spin3/2
Quadrupole Moment
Discovery Year1851
Parity-

227Ac Decay Modes
Decay ModeIntensity
β (β decay)98.62%
α (α emission)1.38%

228Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
228.031019685 ± 0.000002247 Da
Mass Number228
G-Factor
Half Life
6.15 ± 0.02 h
Spin3
Quadrupole Moment
Discovery Year1908
Parity+

228Ac Decay Modes
Decay ModeIntensity
β (β decay)100%

229Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
229.032947 ± 0.000013 Da
Mass Number229
G-Factor
Half Life
62.7 ± 0.5 m
Spin3/2
Quadrupole Moment
Discovery Year1952
Parity+

229Ac Decay Modes
Decay ModeIntensity
β (β decay)100%

230Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
230.036327 ± 0.000017 Da
Mass Number230
G-Factor
Half Life
122 ± 3 s
Spin1
Quadrupole Moment
Discovery Year1973
Parity+

230Ac Decay Modes
Decay ModeIntensity
β (β decay)100%
β SF (β-delayed fission)1.2%

231Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
231.038393 ± 0.000014 Da
Mass Number231
G-Factor
Half Life
7.5 ± 0.1 m
Spin1/2
Quadrupole Moment
0
Discovery Year1973
Parity+

231Ac Decay Modes
Decay ModeIntensity
β (β decay)100%

232Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
232.042034 ± 0.000014 Da
Mass Number232
G-Factor
Half Life
1.98 ± 0.08 m
Spin1
Quadrupole Moment
Discovery Year1986
Parity+

232Ac Decay Modes
Decay ModeIntensity
β (β decay)100%

233Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
233.044346 ± 0.000014 Da
Mass Number233
G-Factor
Half Life
143 ± 10 s
Spin1/2
Quadrupole Moment
0
Discovery Year1983
Parity+

233Ac Decay Modes
Decay ModeIntensity
β (β decay)100%

234Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
234.048139 ± 0.000015 Da
Mass Number234
G-Factor
Half Life
45 ± 2 s
Spin1
Quadrupole Moment
Discovery Year1986
Parity+

234Ac Decay Modes
Decay ModeIntensity
β (β decay)100%

235Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
235.05084 ± 0.000015 Da
Mass Number235
G-Factor
Half Life
62 ± 4 s
Spin1/2
Quadrupole Moment
0
Discovery Year2006
Parity+

235Ac Decay Modes
Decay ModeIntensity
β (β decay)100%

236Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
236.054988 ± 0.000041 Da
Mass Number236
G-Factor
Half Life
4.5 ± 3.6 m
Spin3
Quadrupole Moment
Discovery Year2010
Parity+

236Ac Decay Modes
Decay ModeIntensity
β (β decay)100%

237Ac

AbundanceRadioactive ☢️
Relative Atomic Mass
237.057993 ± 0.000429 Da
Mass Number237
G-Factor
Half Life
Spin1/2
Quadrupole Moment
0
Discovery Year
Parity+

237Ac Decay Modes
Decay ModeIntensity
β (β decay)%

History

André-Louis Debierne, a French chemist, discovered actinium in 1899. He separated it from pitchblende residues left by Marie and Pierre Curie after they had extracted radium. Friedrich Oskar Giesel independently discovered actinium in 1902 as a substance being similar to lanthanum. From the Greek aktis, aktinos, meaning beam or ray

DiscoverersAndré Debierne
Discovery LocationFrance
Discovery Year1899
Etymology (Name Origin)Greek: akis, aktinos (ray).
Pronunciationak-TIN-i-em (English)
Actinium is highly radioactive
Actinium glows in the dark with a pale blue light

Uses

Actinium is used as an active element of radioisotope thermoelectric generators, for example in spacecraft. The medium half-life of 227Ac makes it very convenient radioactive isotope in modeling the slow vertical mixing of oceanic waters. 225Ac is applied in medicine to produce 213Bi in a reusable generator or can be used alone as an agent for radiation therapy. It has no significant commercial applications.

Sources

Extremely rare, found in all uranium ores. Usually obtained by treating radium with neutrons in a reactor.

Abundance
Abundance in Earth's crust
0.00000000055 mg/kg
Abundance in Oceans
Abundance in Human Body
0 %
Abundance in Meteor
Abundance in Sun
0 %
Abundance in Universe
0 %

Nuclear Screening Constants