is a radioactive chemical element
with the symbol Ac
and atomic number
89, which was discovered in 1899
, the earliest discovered of the radioactive elements.
Actinium is a silvery, radioactive
, metallic element. Due to its intense radioactivity, actinium glows in the dark with a pale blue light. The chemical behavior of actinium is similar to that of the rare earth element lanthanum
Actinium is found only in traces in uranium ores as 227Ac, an α 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. The actinium isotope 227Ac is a transient member of the actinium series decay chain, which begins with the parent isotope 235U (or 239Pu) and ends with the stable lead isotope 207Pb. Another actinium isotope (225Ac) is transiently present in the neptunium series decay chain, beginning with 237Np (or 233U) and ending with near-stable bismuth (209Bi).
It is about 150 times as radioactive as radium, making it valuable as a neutron source
for energy. Otherwise it has no significant industrial applications.
225Ac is used in medicine to produce 213 in a reusable generator or can be used alone as an agent for radio-immunotherapy for Targeted Alpha Therapy (TAT). 225Ac was first produced artificially by the ITU in Germany using a cyclotron and by Dr Graeme Melville at St George Hospital in Sydney using a linac in 2000.
Actinium was discovered in 1899 by André-Louis Debierne
, a French chemist, who separated it from pitchblende
as a substance being similar to titanium
(1899) or similar to thorium
(1890). Friedrich Oskar Giesel
independently discovered actinium in 1902 as a substance being similar to lanthanum
and called it "emanium" in 1904. After a comparison of substances in 1904, Debierne's name was retained because it had seniority.
The history of the discovery stayed questionable and in publications from 1971 and later in 2000 showed that the claims of André-Louis Debierne in 1904 conflict with the publications in 1899 and 1890.
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
in a nuclear reactor. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300°C.
Naturally occurring actinium is composed of 1 radioactive isotope
Ac. 36 radioisotopes
have been characterized with the most stable being 227
Ac with a half-life
of 21.772 y
Ac with a half-life of 10.0 days
, and 226
Ac with a half-life of 29.37 h
. 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 217
Ac 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 u (206Ac) to 236 u (236Ac).
Ac is extremely radioactive, and in terms of its potential for radiation induced health effects, 227
Ac is even more dangerous than plutonium
. Ingesting even small amounts of 227
Ac would be fatal.
Actinium compounds, along with advanced circuitry are used in a time travel device in Excalibur: Morgana's Revenge