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History

Actinium was discovered in 1899 by Andre-Louis Debierne, a French chemist, who separated it from pitchblende.  Friedrich Oskar 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 a rare, extremely radioactive metal that glows in the dark.   Eventual priority was given to Debierne's work.

Characteristics

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

Occurrence

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

Applications

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

²²⁵Ac is used in medicine to produce ²¹³Bi in a reusable generator or can be used alone as an agent for radio-immunotherapy for Targeted Alpha Therapy (TAT). ²²⁵Ac was first produced artifically by the ITU in Germany using a cyclotron and by Dr Graeme Melville at St George Hospital in Sydney using a linac in 2000.

Isotopes

Naturally occurring actinium is composed of 1 radioactive isotope; ²²⁷Ac. 36 radioisotopes have been characterized with the most stable being ²²⁷Ac with a half-life of 21.772 years, ²²⁵Ac with a half-life of 10.0 days, and ²²⁶Ac 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.  The shortest-lived isotope of actinium is ²¹⁷Ac which decays through alpha decay and electron capture.  It has a half-life of 69 ns.   Actinium also has 2 meta states.

Purified ²²⁷Ac 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 (²⁰⁶Ac) to 236 amu (²³⁶Ac).

Samples of actinium quickly decay to thorium and francium.  The element is obtained as an impurity in pitchblende, an ore mined for its uranium content. One-tenth of one gram of actinium can be recovered from 1 ton of pitchblende.

Precautions

227Ac is extremely radioactive, and in terms of its potential for radiation induced health effects, 227Ac is even more dangerous than plutonium.  Ingesting even small amounts of 227Ac would present a serious health hazard.

(Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees C. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond