Actinium (Ac)

Actinium is a rare-earth element that belongs to the family of actinides in the periodic table. The actinide series of elements is highly significant due to their radioactive properties. They comprise a group of 15 chemical elements that share the same chemical and physical properties. 

Physical and Chemical Properties of Actinium

The symbol in the periodic table of elementsAc
Atomic number89
Atomic weight (mass)227 g.mol-1
Group number3
Physical stateA radioactive metal
Electronegativity according to Pauling1.1
Density10.07 at 20°C
Melting point1050 °C
Boiling point3250 °C
Van der Waals radiusUnknown
Ionic radiusUnknown
Electronic shell[ Rn ] 6d1 7s2
The energy of first ionization664.6 kJ.mol-1
The energy of second ionization1165.5 kJ.mol-1
Discovery dateIn 1899 (1902), by André Debierne

With the periodic table symbol Ac, atomic number 89, atomic mass of 227 g.mol -1, and electronic configuration [Rn] 6d17s2, actinium reaches its boiling point at 3250 °C, while the melting point is achieved at 1050 °C. This member of the actinide family of elements in the periodic table has an electronegativity of 1.1 according to Pauling, whereas the atomic radius according to van der Waals is unknown. 

Actinium displays an oxidation state of +3, which is a chemical property related to lanthanum. The powerful radioactive properties of actinium give this element its most notable physical characteristic – the pale blue glow in the dark. But, it’s not the substance that emits the blue light. 

Since actinium is way more radioactive than radium, it emits an enormous quantity of electrons that stimulate oxygen molecules in the surrounding air. The energy released by the ionized oxygen appears as a pale blue glow from the radioactive substance.  

How Was Actinium Discovered?

The French chemist André-Louis Debierne (14 July 1874, Paris, France – 31 August 1949, Paris, France) is the first scientist who discovered this periodic table element. Debierne managed to isolate actinium by exploring a pitchblende, i.e., remainders of uranium ore (uranium oxide, U3O8) from the experiments on radium carried out by the Nobel-winning chemists Marie Curie and Pierre Curie. 

According to the findings of the French chemist, Debierne, the newly-discovered substance named actinium shares the chemical properties of titanium and thorium. This discovery took place in 1899, while Debierne was trying to separate rare earth oxides. 

How Did Actinium Get Its Name?

Three years later, after Debierne discovered actinium, Friedrich Oskar Giesel ( 20 May 1852, Winzig, Germany – 13 November 1927, Braunschweig, Germany) discovered this element while conducting his scientific research, without knowing that it had already been discovered. His results showed similarities between actinium and lanthanum. In 1904, Giesel labeled the new element as “emanium”. 

Since there were two independent discoveries of the same chemical element, several other scientists compared Debierne and Giesel’s research. In the 1970s, the first Canadian female nuclear physicist and two German chemists (Harriet Brooks, Otto Hahn, and Otto Sackur) comprised the scientific research team that confirmed the chemical properties of the new substance and decided to keep its first name. In this way, Debierne holds the honor of being the first chemist to discover actinium

Where Can You Find Actinium?

Actinium can be found in microscopic traces in uranium or thorium ore. Only 0.15 mg of actinium can be found in a tone of pitchblende ore. Due to its scarcity, this chemical element is often produced in labs. Its production is costly and dangerous, so the application of actinium is limited to scientific, energetic, and medical uses, such as in nuclear reactors, radiation therapy, etc.

Nuclear Medicine (Radiation Therapy)

Nuclear medicine is a biology branch that uses small doses of radioactive substances to examine and treat malignant (cancerous) tumors. By implementing radiation therapy (or radiotherapy) in the treatments, nuclear medicine utilizes the high intensity of the radioactive beams to destroy malignant tumor cells. More specifically, actinium-255 (Ac-255) isotope with a half-life of 10 days is used in the treatment of cancer patients. This type of radiation therapy is typically performed via extremely short electromagnetic waves of high energy. 

These high-energy waves are produced in a special machine that radiates the beams precisely onto the tumorous lump formed on a particular tissue. The beams protrude the mutated neuron cell’s body and destroy the genetic material they carry. That’s how radiation therapy controls or completely stops the multiplication and growth of cancerous cells in the body. 

Spacecraft Power Systems

Since there are no gas stations for spacecraft in space, the production of neutrons is the only solution for fueling the vehicles that are on a mission of exploring the Solar System. 

Due to the high activity level of actinium, spacecraft power systems use the radioisotope power and neutron irradiation that is generated by the radioactive elements. When actinium (or any other radioactive element) breaks down, it generates heat that is used by these power systems as a source of energy.  

Nuclear Power Reactors

A nuclear power reactor is a machine that generates electricity by splitting the atoms of particular chemical elements apart and producing neutrons by a controlled nuclear reaction. That’s why radioactive elements are used as fuel.  

How Dangerous Is Actinium?

Actinium imposes enormous health hazards due to its intense radioactivity. Despite being used to cure cancer and heal the body’s tissues, healthy cells are also destroyed alongside tumorous cells during radiation therapy in cancer patients. The body reacts to the destruction of healthy cells due to radioactivity exposure by triggering:

  • Hair loss;
  • Nausea; 
  • Vomiting;
  • Fatigue;
  • Open sores on the skin and in the mouth. 

Exposure to radiation can also lead to severe illnesses such as leukemia, stillbirths, lowered immunological defenses of the body, etc. 

Environmental Effects of Actinium

When radioactive waste is improperly discarded, it pollutes nature – the rivers, seas, oceans, forests – and the entire ecosystem. Spreading through the food chain and destroying the natural habitats of animals, birds, fish, and humans, radiation can lead to the complete destruction of various gene pools as well as the ecosystems on the planet.  

Actinium Isotopes

This chemical element has more than 25 isotopes, among which we could mention the following:

  • Actinium-223 (232Th(d,7n)→227Pa(α)→223Ac) – With a half-life of 2.1 minutes, this isotope is used to produce fuel for nuclear weapons and nuclear reactors.
  • Actinium-225 (232Th(n,γ)→233Th(β)→233Pa(β)→233U(α)→229Th(α)→225Ra(β)→225Ac) – This actinium isotope has notable application in nuclear medicine, as a part of the treatment for cancer patients. Its half-life is 9.92 days. Actinium-255 undergoes alpha decay to francium-221 with a half-life of ten days. Its isotopes emit alpha particles that do not produce gamma rays. 
  • Actinium-227 (235U(α)→231Th(β)→231Pa(α)→227Ac) – The half-life of this purified actinium isotope is 21.77, which makes it one of the most stable actinium isotopes. It’s used for neutron production. Actinium-277 undergoes alpha decay to francium-223 with a half-life of 22.00 minutes.
  • Actinium-228 (232Th(α)→228Ra(β)→228Ac) – Apart from being used as a source of neutron production and an element of the radiation therapy of patients suffering from a malign tumor, this actinium isotope has no additional application. 
  • Actinium-229 (228Ra(n,γ)→229Ra(β)→229Ac) – With a half-life of 1.04 hours, this is one of the least stable isotopes of actinium with no significant commercial use. 
  • Actinium-230 (232Th(d,α)→230Ac) is a neuron-rich isotope of actinium with a half-life of 122s.
  • Actinium-217 is the isotope of this radioactive chemical element with the shortest half-life of only 69ns.

Actinium Decay Products

The 4n+3 decay chain of uranium-235 comprises the following chemical elements: radium, radon, francium, lead, protactinium, thallium, thorium, bismuth, astatine, and actinium. All of these elements are found in uranium ores in varying quantities and are labeled as the “actinium series” or “actinium cascade”. These emit alpha-particles.

nuclidehistoric name (short)historic name (long)decay modehalf-life


energy released, MeVproduct of decay
251Cf  α900.6 a6.176247Cm
247Cm  α1.56·107 a5.353243Pu
243Pu  β4.95556 h0.579243Am
243Am  α7388 a5.439239Np
239Np  β2.3565 d0.723239Pu
239Pu  α2.41·104 a5.244235U
235UAcUActin Uraniumα7.04·108 a4.678231Th
231ThUYUranium Yβ25.52 h0.391231Pa
231PaPaProtactiniumα32760 a5.150227Ac
227AcAcActiniumβ 98.62%

α 1.38%

21.772 a0.045




227ThRdAcRadio-actiniumα18.68 d6.147223Ra
223FrAcKActinium Kβ 99.994%

α 0.006%

22.00 min1.149




223RaAcXActinium Xα11.43 d5.979219Rn
219At  α 97.00%

β 3.00%

56 s6.275





Actinium Emanation

α3.96 s6.946215Po
215Bi  β7.6 min2.250215Po
215PoAcAActinium Aα 99.99977%

β 0.00023%

1.781 ms7.527




215At  α0.1 ms8.178211Bi
211PbAcBActinium Bβ36.1 min1.367211Bi
211BiAcCActinium Cα 99.724%

β 0.276%

2.14 min6.751




211PoAcC’Actinium C’α516 ms7.595207Pb
207TlAcC”Actinium C”β4.77 min1.418207Pb
207PbAcDActinium D.stable..

Chemical Compounds of Actinium

The list of chemical compounds of actinium includes:

  • Actinium fluoride (AcF3);
  • Actinium (III) oxide (Ac2O3);
  • Uraninite (UO2);
  • DOTA / Tetraxetan (C16H28N4O8);
  • Actinium dihydride (AcH2);
  • Actinium triiodide (AcI3).

5 Interesting Facts and Explanations

  1. The meaning behind the name of the chemical element actinium derives from the Greek word aktinos, meaning “beam” or “ray”. This refers to its property of glowing in the dark.
  2. Debierne managed to extract actinium from uranium ore by using ammonia. 
  3. Radiology analyzes and diagnoses physical anatomy changes, while nuclear medicine deals with molecular structures, cells, chemical processes, and interactions within a biological system. 
  4. The family of actinides in the periodic table of elements is made up of actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium.
  5. The term gene pool refers to the collection of the entire genetic material of a given generation. People in a given country, the fish in a lake, or the animals of a particular rain forest are some examples of gene pools.