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Radium - Actinium - Thorium

Full table
Name, Symbol, Numberactinium, Ac, 89
Chemical series Actinides
Group, Period, Block3 , 7 , f
Density, Hardness 10070 kg/m3, n/a
Appearance silvery
Atomic Properties
Atomic weight (227) amu
Atomic radius (calc.) 195 (n/a) pm
Covalent radius n/a pm
van der Waals radius n/a pm
Electron configuration [Rn]6d6d17s2
e- 's per energy level 2, 8,18,32,18, 9, 2
Oxidation states (Oxide) 3 (neutral)
Crystal structure face centered cubic
Physical Properties
State of matter solid (__)
Melting point 1323 K (1922 °F)
Boiling point 3473 K (5792 °F)
Molar volume 22.55 ×1010-3 m3/mol
Heat of vaporization n/a kJ/mol
Heat of fusion 62 kJ/mol
Vapor pressure unknown Pa at 1323 K
Velocity of sound unknown m/s at 293.15 K
Electronegativity 1.1 (Pauling scale)
Specific heat capacity unknown J/(kg*K)
Electrical conductivity unknown 106/m ohm
Thermal conductivity 12 W/(m*K)
1st ionization potential 499 kJ/mol
2nd ionization potential 1170 kJ/mol
3rd ionization potential unknown kJ/mol
4th ionization potential unknown kJ/mol
Most Stable Isotopes
isoNAhalf-life DMDE MeVDP
225Ac{syn.}10 days α5.935221Fr
226Ac{syn.}29.37 hoursβ-1.117226Th
226Ac{syn.}29.37 hourse capture0.640226Ra
226Ac{syn.}29.37 hoursα5.536222Fr
227Ac100 %21.773 yearsβ-0.045227Th
227Ac100 %21.773 yearsα5.042223Fr
SI units & STP are used except where noted.
Actinium is a chemical element in the periodic table that has the symbol Ac and atomic number 89.

Table of contents
1 Notable Characteristics
2 Applications
3 History
4 Occurrence
5 Compounds
6 Isotopes
7 Precautions
8 External Links

Notable Characteristics

Actinium is a silvery radioactive metallic element. Actinium glows in the dark due to its intense radioactivity with an eerie blue light. It is found only in traces in uranium ores as 227-Ac, an &alpha and β emitter with a half-life of 21.773 years. One ton of uranium ore contains about a tenth of a gram of actinium.


It is about 150 times as radioactive as radium, making it valuable as a neutron source. Otherwise it has no significant industrial applications.

Actinium-225 is used in medicine to produce Bi-213 in a reusable generator or can be used alone as an agent for radio-immunotherapy.


Actinium was discovered in 1899 by André-Louis Debierne, a French chemist, who separated it from pitchblende. Friedrich Otto Giesel independently discovered actinium in 1902. The chemical behavior of actinium is similar to that of the rare earth lanthanum.

The word actinium comes from the Greek aktis, aktinos, meaning beam or ray.


Actinium is found in trace amounts in uranium ore, but more commonly is made in milligram amounts by the neutron irradiation of 226-Ra in a nuclear reactor. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees C.



Naturally occurring actinium is composed of 1 radioactive isotope; with 227-Ac being the most abundant (100% natural abundance). 27 radioisotopes have been characterized with the most stable being 227-Ac with a half-life of 21.773 years, 225-Ac with a half-life of 10 days, and 226-Ac with a half-life of 29.37 hours. All of the remaining radioactive isotopes have half-lifes that are less than 10 hours and the majority of these have half lifes that are less than 1 minute. This element also has 2 meta states.

Purified actinium-227 comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.773-year half-life.

The isotopes of actinium range in atomic weight from 206 amu (206-actinium) to 234 amu (234-actinium).   


Actinium-227 is extremely radioactive, and in terms of its potential for radiation induced health effects, actinium-227 is about as dangerous as plutonium. Ingesting even small amounts of actinium-227 would represent a serious health hazard.

External Links