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What is Actinium

A radioactive metal, actinium (pronounced as ak-TIN-ee-em) belongs to the family of actinide metals and denoted by the chemical symbol Ac [1].

Actinium Symbol

Actinium Isotopes

It has 29 isotopes out of which actinium-227 is the most stable one, having a half-life of 21.17 years. After which, it either undergoes alpha decay into francium-223, or beta decay into thorium-227 [3].

Where is Actinium Found

The element occurs in uranium ore deposits formed as a result of radioactive decay of uranium and its other radioisotopes. Its abundance in earth’s crust is estimated to be 0.0005 parts per trillion by mass [4].


Origin of its Name: It derives its name from the Greek word, ‘aktis’, meaning a ‘beam’ or ‘ray’.

Who Discovered Actinium: Andre Debierne, a French Chemist, discovered the element.

When and How was it Discovered

In 1899, Debierne at Paris while finding out new methods to separate rare earth oxides extracted the element from uranium-rich pitchblende ores. In 1902, Friedrich Otto Giesel who was unaware of Debierne’s discovery independently worked on the same mineral ore to extract the element and even named it emanium. However, the original name ‘actinium’ was decided to be retained [1, 2].


Classification and Position of the Element on the Periodic Table [1]

Group Unknown
Period 7
Block d

Location of Actinium in the Periodic Table

Properties of Actinium [1, 2, 3]

General Properties

Relative atomic mass 227
Atomic mass 227 atomic mass units

Physical Properties

Color/appearance Silver white
Luster Unknown
Odor Unknown
Malleability Unknown
Ductility Unknown
Melting point/freezing point  1050 °C (1922 °F)
Boiling point 3200 °C (5792 °F)
Density 10 g/cm3
State of matter at room temperature  (solid/liquid/gas) Solid
Hardness Unknown

Chemical Properties

Flammability Unknown
Oxidation state/Oxidation number (+2), +3

Atomic Data of Actinium [1, 2, 3]

Atomic number 89
Valence electrons 3
Quantum numbers Unknown
Electron configuration (noble gas configuration) [Rn] 6d17s2
Atomic structure
– Number of electrons 89
– Number of neutrons 138
– Number of protons 89
Radius of Atom
 – Atomic radius 3.48 Å
 – Covalent radius 2.47 Å
Electronegativity 2.01
Ionization energy


1st 2nd 3rd 4th 5th 6th 7th
498.83 1133.7

Actinium Bohr Model

Common Uses of Actinium

Although a good source of alpha rays, it has no specific commercial applications, except in laboratory research [2].

Due to actinium’s high activity levels, it might be effective in generating neutrons. While some research studies show the effectiveness of actinium-225 in the treatment of prostate cancer [5], actinium-227 might be useful in thermoelectric generators of spacecraft [4].

Actinium Health Hazards

Accidental ingestion of Ac leads to deposition in the bones and liver, causing severe damage like cancer due to radioactive decay [4].

Actinium Pictures

Interesting Facts

  • Debierne may have worked with Marie Curie during the actinium’s discovery as the pitchblende sample used by him was the one from which radium and polonium had already been extracted by the latter [4].
  • Actinium glows blue in the dark as a result of ionization of gases in the air caused by its radioactivity [4].
  • It is about 150 times heavier than radium [4].

What is the Cost of Actinium

Since production of the metal on a commercial scale is expensive, it cannot be availed outside of laboratory production.



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