Francium

Francium (valence electron.

Francium was discovered by ultracold gas at Stony Brook in 1997.^[3]

Characteristics

Francium is less stable than any other element lighter than astatine, the next least stable element, has a maximum half-life of 8.5 hours.^[4] All isotopes of francium decay into either astatine, radium, or radon.^[4]

Francium is an m at its melting point.^[8] Francium water-soluble.^[11]

Applications

Due to its instability and rarity^{[12][13][14][15][16]} there are no commercial applications for francium. It has been used for research purposes in the fields of biology and of atomic structure. Its use as a potential diagnostic aid for various cancers has also been explored,^[4] but this application has been deemed impractical.^[14]

Francium's ability to be synthesized, trapped, and cooled, along with its relatively simple subatomic particles.^[17] Studies on the light emitted by laser-trapped francium-210 ions have provided accurate data on transitions between atomic energy levels which are fairly similar to those predicted by quantum theory.^[18]

History

As early as 1870, chemists thought that there should be an alkali metal beyond eka-caesium.^[19] Research teams attempted to locate and isolate this missing element, and at least four false claims were made that the element had been found before an authentic discovery was made.

Erroneous and incomplete discoveries

Russian chemist D. K. Dobroserdov was the first scientist to claim to have found eka-caesium, or francium. In 1925, he observed weak radioactivity in a sample of potassium, another alkali metal, and concluded that eka-caesium was contaminating the sample.^[20] He then published a thesis on his predictions of the properties of eka-caesium, in which he named the element russium after his home country.^[21] Shortly thereafter, Dobroserdov began to focus on his teaching career at the Polytechnic Institute of Odessa, and he did not pursue the element further.^[20]

The following year, English chemists Gerald J. F. Druce and Frederick H. Loring analyzed X-ray photographs of manganese(II) sulfate.^[21] They observed spectral lines which they presumed to be of eka-caesium. They announced their discovery of element 87 and proposed the name alkalinium, as it would be the heaviest alkali metal.^[20]

In 1930, Fred Allison of the Alabama Polytechnic Institute claimed to have discovered element 87 when analyzing magneto-optical machine. Allison requested that it be named virginium after his home state of Virginia, along with the symbols Vi and Vm.^[21][22] In 1934, however, H.G. MacPherson of UC Berkeley disproved the effectiveness of Allison's device and the validity of this false discovery.^[23]

In 1936, Romanian chemist Horia Hulubei and his French colleague Yvette Cauchois also analyzed pollucite, this time using their high-resolution X-ray apparatus.^[20] They observed several weak emission lines, which they presumed to be those of element 87. Hulubei and Cauchois reported their discovery and proposed the name moldavium, along with the symbol Ml, after Moldavia, the Romanian province where they conducted their work.^[21] In 1937, Hulubei's work was criticized by American physicist F. H. Hirsh Jr., who rejected Hulubei's research methods. Hirsh was certain that eka-caesium would not be found in nature, and that Hulubei had instead observed Marguerite Perey's recently discovered francium. Perey, however, continuously criticized Hulubei's work until she was credited as the sole discoverer of element 87.^[20]

Perey's analysis

Eka-caesium was truly discovered in 1939 by beta decay to alpha decay in actinium-227. Her first test put the alpha branching at 0.6%, a figure which she later revised to 1%.^[24]

Perey named the new isotope actinium-K (now referred to as francium-223)^[19] and in 1946, she proposed the name catium for her newly discovered element, as she believed it to be the most rhenium in 1925.^[19] Further research into francium's structure was carried out by, among others, Sylvain Lieberman and his team at CERN in the 1970s and 1980s.^[26]

Occurrence

Natural

Francium-223 is the result of the alpha decay of actinium-227 and can be found in trace amounts in astatine.^[4][14]

Synthesized

Francium can be synthesized in the nuclear reaction ¹⁹⁷Au + ¹⁸O → ²¹⁰Fr + 5n. This process, developed by Stony Brook Physics, yields francium isotopes with masses of 209, 210, and 211,^[29] which are then isolated by the ions.^[24] Francium has not yet, as of 2006, been synthesized in amounts large enough to weigh.^{[3][4][14][30]}

Isotopes

Main article: Isotopes of francium

There are 34 known isotopes of francium ranging in metastable nuclear isomers.^[3] Francium-223 and francium-221 are the only isotopes that occur in nature, though the former is far more common.^[31]

Francium-223 is the most stable isotope with a half-life of 21.8 minutes,^[3] and it is highly unlikely that an isotope of francium with a longer half-life will ever be discovered or synthesized.^[24] Francium-223 is the fifth product of the alpha decay path to astatine-219 (5.4 MeV decay energy).^[32]

Francium-221 has a half-life of 4.8 minutes.^[3] It is the ninth product of the neptunium decay series as a daughter isotope of actinium-225.^[16] Francium-221 then decays into astatine-217 by alpha decay (6.457 MeV decay energy).^[3]

The least stable ground state isotope is francium-215, with a half-life of 0.12 μs. (9.54 MeV alpha decay to astatine-211):^[3] Its metastable isomer, francium-215m, is less stable still, with a half-life of only 3.5 ns.^[33]

See also

References