Steve Marsden’s


  • 90
    This page contains brief profiles and pictures of each of the Actinide metals. More information can be found via the WWW links following each element. However, as these links are to other servers on the Internet you will need to use the BACK button on your browser to return to this page. Credits for the photos and principal links can be found at the end of this document.
  • Th

    Thorium was discovered by Berzelius in 1828 and named for the Norse god of thunder, Thor. It is a gray, radioactive metal which is fairly abundant in the earth's crust (more than twice as much as tin) and is the first of the so-called "actinide" series which ends with lawrencium (element 103). The long half-life of the principal isotope, Th-232, (about 1010 years) insures that there will be plenty for quite some time to come!

    The metal is fairly soft and malleable but darkens slowly in air due to oxidation. It reacts slowly with water at room temperature.

    Applications of thorium include some special magnesium alloys and photosensors. The oxide is used in high-quality lenses. An isotope of thorium can be "bred" into uranium-234 by bombardment with slow neutrons. The U-234 is a fissile form of uranium and can be used in power plants.

    More background information on Th More data on Th
  • Pa

    Discovered in 1913 by Fajans and Göhring, and then isolated in 1934 by Grosse, protactinium is named from the Greek proto + actinium (parent of actinium). The silvery-white metal (photo above is of the oxide) is extrememly rare, very radioactive and highly poisonous. Originally called brevium by its discoverers because of the short life-time of the transition between Th-234 and U-234, a longer-lived isotope was eventually isolated and called protoactinium by Grosse. The name was shortened to its present form in 1949.

    About 60 tons of pitchblende ore (which contains uranium, radium, and a host of other radioactive elements) yields about 125 grams of protactinium.

    More background information on Pa More data on Pa
  • U

    Uranium was named for the planet Uranus and discovered in 1789 by Klaproth. Isolation came in 1841 by Péligot and the radioactivity of the element was noted by Becquerel in 1896.

    The pure metal is heavy, silver and lustrous. It tarnishes slowly in air and reacts with boiling water.

    Most of the naturally occurring uranium is the isotope U-238. This form of uranium is not fissionable, i.e., it cannot be used in atomic weapons or power plants. A much smaller percentage of naturally occurring uranium is the isotope U-235, which is fissionable. The process of "enriching" uranium to increase the proportion of U-235 in a sample is expensive and tedious but necessary to produce fuel that is usable in power plants and material for weapons.

    The U-238 is not completely useless, however, as it can be "bred" into Pu-239 by bombardment with slow neutrons. This is how weapons-grade plutonium is produced. The use of Pu-239 in power plants is a controversial subject due to its toxicity and the fear of diversion by terrorist groups.

    More background information on U More data on U Uranium Information Center, Australia
  • Np

    Neptunium (named for the planet Neptune) was the first of the transuranium elements to be synthesized (photo above is of the oxide). The synthesis took place at Berkeley, California, after initial examination of the decay products of U-235 suggested the possibility of a new element. Credit for the discovery goes to McMillan and Abelson in 1940. Although the neptunium on which the characterization work was done was synthesized in a cyclotron, we now know that minute amounts of the element exist in the environment (the longest-lived isotope has a half-life of about 2 million years). All isotopes of the metal are radioactive.

    More background information on Np More data on Np
  • Pu

    Discovered by Seaborg (see element 106) in 1941, plutonium was named for the 9th planet, completing the series of elements named for planets which begins with uranium. Evidence for the existence of plutonium was obtained from work with samples of neptunium and the eventual synthesis in fact results from the beta decay of neptunium-239.

    The longest-lived isotope of plutonium is Pu-244 with a half-life of 82 million years. However the isotope of chief interest is Pu-239 which, like U-235, is fissionable. Most of the nuclear weapons built by the "great powers" today are based on Pu-239 which is derived from U-238 in special "breeder" reactors. Pu-239 is also a by-product of normal fission power reactors and accounts for a good deal of the concern over nuclear waste by-products since it is both highly radioactive and exceptionally toxic. Also, since the critical mass of plutonium is only about one third that of U-235, the possibility for terrorist diversion of the material is considered a serious matter.

    A piece of plutonium about the size of a softball would feel hot to the touch because of the high level of alpha particle radiation given off. A somewhat larger piece of the metal would boil water within minutes. Plutonium is occasionally used in deep-space probes as a source of energy (too far from the sun for effective solar power), the heat being directly converted into electricity by a special device.

    More background information on Pu More data on Pu
  • Am

    Element 95, americium (photo above is actually of the oxide), was discovered after element 96, but only just. Seaborg (see element 106), James, Morgan and Ghiorso share credit for the synthesis in 1944. Since the element is similar to europium (and below it in the periodic table) it seemed sensible to name element 105 for the American continent.

    Americium-241 is the isotope first produced and is manufactured today in kilogram quantities for use in high-precision measuring devices and some home smoke detectors. All isotopes of the metal are radioactive, the longest half-life being about 7400 years.

    More background information on Am More data on Am
  • Cm

    "Simply" by bombarding the newly characterized Pu-239 with alpha particles, the Berkeley team of Seaborg (see element 106), James and Ghiorso managed to produce element 96 even before any element 95 had been made (the photo above shows a pellet of Cm prepared at Oak Ridge; the glow is caused by the radioactive decay). Named in honor of Pierre and Marie Curie in 1944, curium is another actinide metal.

    More background information on Cm More data on Cm
  • Bk

    Visible as the small gold spot (arrow) in the photograph above, berkelium was synthesized by Thompson, Ghiorso and Seaborg (see element 106) in 1949 and named for the site of its discovery: Berkeley, California. The initial synthesis was achieved by bombarding Am-241 with alpha particles. Two neutrons are ejected and a nucleus of Bk-243 results. The longest-lived isotope of berkelium is Bk-247 with a half-life of 1400 years.

    More background information on Bk More data on Bk
  • Cf

    The fifth element in succession to emerge from the Berkeley, California cyclotron was element 98, californium (named after the State of origin). Credit for the synthesis is given to the team of Thompson, Street, Ghiorso and--of course--Seaborg (see element 106). The photo above shows about 20 micrograms as a circular spot plated on a platinum disk. Synthesis was achieved by bombarding Cm-242 with alpha particles. A neutron is ejected and a nucleus of Cf-245 results. The longest-lived isotope of californium, Cf-251, has a half-life of 890 years.

    More background information on Cf More data on Cf
  • Es

    Credit for the synthesis of element 99 was given to the Berkeley team of Ghiorso et. al. in 1952 and the radioactive metal was named for Albert Einstein. The photo above shows about 0.3 micrograms of an unidentified Es compound. Evidence for the feasibility of the synthesis came from the debris of the first hydrogen bomb explosion in which U-238 was apparently transformed into U-253 which becomes Es-253 by the loss of seven beta particles.

    The laboratory synthesis of Es-253 begins with Pu-239 and goes through a five step process. The longest-lived isotope is Es-254 with a half-life of 276 days.

    More background information on Es More data on Es
  • Fm
    no images of Fermium available

    From evidence detected in the debris of the first hydrogen bomb test, the Berkeley team of Ghiorso et. al. succeeded in the synthesis of element 100 in 1952 and named it fermium after the Italian physicist Enrico Fermi. Fm-254 was produced by neutron bombardment of Es-253.

    The longest-lived isotope of fermium is Fm-257 with a half-life of 80 days.

    More background information on Fm More data on Fm
  • Md
    no images of Mendelevium available

    Mendelevium (after Dmitri Mendeleev) was first synthesized in 1955 by Ghiorso, Harvey, Choppin, Thompson and Seaborg (see element 106). Es-253 was bombarded with alpha particles, ejecting a neutron and yielding a nucleus of Md-256. The most stable isotope is Md-258 with a half-life of 56 days.

    More background information on Md More data on Md
  • No
    no images of Nobelium available

    Discovered by Ghiorso, Sikkeland, Walton and Seaborg (see element 106) and named for Alfred Nobel, element 102 was originally named by a Swedish group working at the Nobel Institute of Physics in Stockholm. Details of their work, however, did not yield the expected results and the credit eventually shifted to the American team which decided to retain the original given name. The most stable isotope is No-259 with a half-life of just about 1 minute.

    More background information on No More data on No
  • Lr
    no images of Lawrencium available

    The last of the actinide metals and only the second of the transuranium elements that Glenn Seaborg was not involved with, element 103 was synthesized in 1961 by Ghiorso, Sikkeland, Larsh and Latimer at the Lawrence Radiation Laboratory (and named for Ernest Lawrence, the inventor of the cyclotron). Lr-256 is the most stable isotope with a half-life of 28 seconds.

    More background information on Lr More data on Lr

Sources: Photos of the elements were taken from the LIFE Science Library book Matter. Background links go to the Periodic Table created at Los Alamos National Laboratories by Robert Husted. Data links go to the primary site of Mark Winter's WebElements, version 2.0, at the University of Sheffield in the United Kingdom.