Francium is a highly radioactive metal that decays into astatine, radium, and radon. As an alkali metal, it has one valence electron.
Francium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. It was the last element discovered in nature, rather than by synthesis. Sony VAIO VGN-Z37GD Battery
[note 2] Outside the laboratory, francium is extremely rare, with trace amounts found in uranium and thorium ores, where the isotope francium-223 continually forms and decays. As little as 20–30 g (one ounce) exists at any given time throughout the Earth's crust; the other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.[1] Sony VAIO VGN-Z37GD/X Battery
Sony VAIO VGN-Z39D Battery
Characteristics
Francium is the most unstable of the naturally occurring elements: its most stable isotope, francium-223, has a maximum half-life of only 22 minutes. In contrast, astatine, the second-least stable naturally occurring element, has a maximum half-life of 8.5 hours.[2]All isotopes of francium decay into either astatine, radium, or radon.[2] Francium is also less stable than all synthetic elements up to element 105.[3] Sony VAIO VGN-Z39D/X Battery
Francium is an alkali metal whose chemical properties mostly resemble those of caesium.[3] A very heavy element with a singlevalence electron,[4] it has the highest equivalent weight of any element.[3] Liquid francium—if such a substance were to be created—should have a surface tension of 0.05092 N/m at its melting point.[5] Sony VAIO VGN-Z41MD/B Battery
Francium’s melting point was claimed to have been calculated to be around 27 °C (80 °F, 300 K).[6] However, the melting point is uncertain because of the element’s extreme rarity and radioactivity. Thus, the estimated boiling point value of 677 °C (1250 °F, 950 K) is also uncertain. Because radioactive elements give off heat, francium would almost certainly be a liquid if enough were to be produced. Sony VAIO VGN-Z41WD/B Battery
Linus Pauling estimated the electronegativity of francium at 0.7 on the Pauling scale, the same as caesium;[7] the value for caesium has since been refined to 0.79, although there are no experimental data to allow a refinement of the value for francium.[8] Francium has a slightly higher ionization energy than caesium,[9] 392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for caesium, as would be expected from relativistic effects, and this would imply that caesium is the less electronegative of the two. Sony VAIO VGN-Z45GD/B Battery
Francium coprecipitates with several caesium salts, such as caesium perchlorate, which results in small amounts of francium perchlorate. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method ofGlendeninand Nelson. It will additionally coprecipitate with many other caesium salts, including the iodate, the picrate, the tartrate(also rubidium tartrate), the chloroplatinate, and the silicotungstate. Sony VAIO VGN-Z45TD/B Battery
It also coprecipitates withsilicotungstic acid, and with perchloric acid, without another alkali metal as a carrier, which provides other methods of separation.[10][11] Nearly all francium salts are water-soluble.[12]
Applications
Due to its instability and rarity, there are no commercial applications for francium. Sony VAIO VGN-Z46GD/B Battery
It has been used for research purposes in the fields of biology[18] and of atomic structure. Its use as a potential diagnostic aid for variouscancers has also been explored,[2] but this application has been deemed impractical.[15]
Francium's ability to be synthesized, trapped, and cooled, along with its relatively simple atomic structure have made it the subject of specialized spectroscopy experiments. Sony VAIO VGN-Z46GD/U Battery
These experiments have led to more specific information regarding energy levels and the coupling constants between subatomic particles.[19] 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 byquantum theory.[20] Sony VAIO VGN-Z46MD/B Battery
As early as 1870, chemists thought that there should be an alkali metal beyond caesium, with an atomic number of 87.[2] It was then referred to by the provisional name eka-caesium.[21] 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. Sony VAIO VGN-Z46SD/B Battery
Erroneous and incomplete discoveries
Soviet 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 incorrectly concluded that eka-caesium was contaminating the sample (the radioactivity from the sample was actually the naturally occurring potassium radioisotope,potassium-40).[22] Sony VAIO VGN-Z46TD/B Battery
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.[23] Shortly thereafter, Dobroserdov began to focus on his teaching career at the Polytechnic Institute of Odessa, and he did not pursue the element further.[22]
The following year, English chemists Gerald J. F. Druce and Frederick H. Loring analyzed X-ray photographs of manganese(II) sulfate.[23] Sony VAIO VGN-Z46TD/R Battery
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.[22]
In 1930, Fred Allison of the Alabama Polytechnic Institute claimed to have discovered element 87 when analyzing polluciteandlepidolite using his magneto-optical machine. Sony VAIO VGN-Z47GD/X Battery
Allison requested that it be named virginium after his home state of Virginia, along with the symbols Vi and Vm.[23][24] In 1934, however, H.G. MacPherson of UC Berkeley disproved the effectiveness of Allison's device and the validity of this false discovery.[25]
In 1936, Romanian physicist Horia Hulubei and his French colleague Yvette Cauchois also analyzed pollucite, this time using their high-resolution X-ray apparatus.[22] Sony VAIO VGN-Z48GD/X Battery
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, afterMoldavia, the Romanian province where Hulubei was born.[23] In 1937, Hulubei's work was criticized by American physicist F. H. Hirsh Jr., who rejected Hulubei's research methods. Sony VAIO VGN-Z48TD/X Battery
Hirsh was certain that eka-caesium would not be found in nature, and that Hulubei had instead observed mercury or bismuth X-ray lines. Hulubei, however, insisted that his X-ray apparatus and methods were too accurate to make such a mistake. Because of this, Jean Baptiste Perrin, Nobel Prize winner and Hulubei's mentor, endorsed moldavium as the true eka-caesium over Marguerite Perey's recently discovered francium. Sony VAIO VGN-Z51WG/B Battery
Perey, however, continuously criticized Hulubei's work until she was credited as the sole discoverer of element 87.[22]
Perey's analysis
Eka-caesium was discovered in 1939 by Marguerite Perey of the Curie Institute in Paris, France when she purified a sample of actinium-227 which had been reported to have a decay energy of 220 keV. Sony VAIO VGN-Z51XG/B Battery
However, Perey noticed decay particles with an energy level below 80 keV. Perey thought this decay activity might have been caused by a previously unidentified decay product, one which was separated during purification, but emerged again out of the pure actinium-227. Various tests eliminated the possibility of the unknown element being thorium, radium, lead, bismuth, or thallium. Sony VAIO VGN-Z530N/B Battery
The new product exhibited chemical properties of an alkali metal (such as coprecipitating with caesium salts), which led Perey to believe that it was element 87, caused by the alpha decay of actinium-227.[21] Perey then attempted to determine the proportion of 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%.[26] Sony VAIO VGN-Z540EBB Battery
Perey named the new isotope actinium-K (now referred to as francium-223)[21] and in 1946, she proposed the name catium for her newly discovered element, as she believed it to be the most electropositive cation of the elements. Irène Joliot-Curie, one of Perey's supervisors, opposed the name due to its connotation of catrather than cation.[21] Sony VAIO VGN-Z540NLB Battery
Perey then suggested francium, after France. This name was officially adopted by the International Union of Pure and Applied Chemistry in 1949,[2] becoming the second element after gallium to be named after France. It was assigned the symbol Fa, but this abbreviation was revised to the current Fr shortly thereafter.[27] Sony VAIO VGN-Z540NMB Battery
Francium was the last element discovered in nature, rather than synthesized, following rhenium in 1925.[21] Further research into francium's structure was carried out by, among others, Sylvain Lieberman and his team at CERN in the 1970s and 1980s.[28]
Natural
Francium-223 is the result of the alpha decay of actinium-227 and can be found in trace amounts in uraniumand thoriumminerals.[3] Sony VAIO VGN-Z550N/B Battery
In a given sample of uranium, there is estimated to be only one francium atom for every 1×1018 uranium atoms.[15] It is also calculated that there is at most 30 g of francium in the earth's crust at any time.[29] This makes it the second rarest element in the crust after astatine.[2][15] Sony VAIO VGN-Z55F Battery
Sony VAIO VGN-Z55TG/B Battery
Synthesized
This process, developed by Stony Brook Physics, yields francium isotopes with masses of 209, 210, and 211,[31] which are then isolated by the magneto-optical trap (MOT).[30] The production rate of a particular isotope depends on the energy of the oxygen beam. An 18O beam from the Stony Brook LINAC creates 210Fr in the gold target with the nuclear reaction 197Au + 18O = 210Fr + 5n. Sony VAIO VGN-Z56GG/B Battery
The production required some time to develop and understand. It was critical to operate the gold target very close to its melting point and to make sure that its surface was very clean. The nuclear reaction imbeds the francium atoms deep in the gold target, and they must be removed efficiently. The atoms diffuse fast to the surface of the gold target and are released as ions, however this does not happen everytime. Sony VAIO VGN-Z56GG/E Battery
The francium ions are guided by electrostatic lenses until they land into a surface of hot yttrium and become neutral again. The francium is then injected into a glass bulb. A magnetic field and laser beams cool and confine the atoms. Although the atoms remain in the trap for only about 20 seconds before escaping (or decaying), a steady stream of fresh atoms replaces those lost, keeping the number of trapped atoms roughly constant for minutes or longer. Sony VAIO VGN-Z56GGX Battery
Initially, about 1000 francium atoms were trapped in the experiment. This was gradually improved and the setup is capable of trapping over 300,000 neutral atoms of francium a time.[1] Although these are neutral "metallic" atoms ("francium metal"), they are in a gaseous unconsolidated state. Enough francium is trapped that a video camera can capture the light given off by the atoms as they fluoresce. Sony VAIO VGN-Z56TG/B Battery
The atoms appear as a glowing sphere about 1 millimeter in diameter. This was the very first time that anyone had ever seen francium. The researchers can now make extremely sensitive measurements of the light emitted and absorbed by the trapped atoms, providing the first experimental results on various transitions between atomic energy levels in francium. Sony VAIO VGN-Z56TG/E Battery
Initial measurements show very good agreement between experimental values and calculations based on quantum theory. Other synthesis methods include bombarding radium with neutrons, and bombarding thorium with protons, deuterons, or helium ions.[26] Francium has not yet, as of 2009, been synthesized in amounts large enough to weigh.[2][3][6][15] Sony VAIO VGN-Z56TG/R Battery
There are 34 known isotopes of francium ranging in atomic mass from 199 to 232.[3] Francium has seven metastable nuclear isomers.[3] Francium-223 and francium-221 are the only isotopes that occur in nature, though the former is far more common.[32] Sony VAIO VGN-Z570N/B Battery
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.[26] Francium-223 is the fifth product of the actinium decay series as the daughter isotope of actinium-227.[17] Sony VAIO VGN-Z57G Battery
Francium-223 then decays into radium-223 by beta decay (1149 keV decay energy), with a minor (0.006%) alpha decay path to astatine-219 (5.4 MeV decay energy).[33]
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.[17] Francium-221 then decays into astatine-217 by alpha decay (6.457 MeV decay energy).[3] Sony VAIO VGN-Z57GG/X Battery
The least stable ground state isotope is francium-215, with a half-life of 0.12 ?s. (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.
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Sony VAIO VGN-Z57GGX Battery
Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226, which has a half-life of 1601 years and decaysinto radon gas. Because of such instability, radium is luminescent, glowing a faint blue. Sony VAIO VGN-Z57TG/X Battery
Radium, in the form of radium chloride, was discovered by Marie Sk?odowska-Curie and Pierre Curie in 1898. They extracted the radium compound from uraninite and published the discovery at the French Academy of Sciences five days later. Radium was isolated in its metallic state by Marie Curie and André-Louis Debierne through the electrolysis of radium chloride in 1910. Sony VAIO VGN-Z58GG/X Battery
Since its discovery, it has given names like radium A and radium C2 to several isotopes of other elements that are decay products of radium-226.
In nature, radium is found in uranium ores in trace amounts as small as a seventh of a gram per ton of uraninite. Sony VAIO VGN-Z58GGX Battery
Radium is not necessary for living organisms, and adverse health effects are likely when it is incorporated into biochemical processes because of its radioactivity and chemical reactivity.
Physical characteristics
Although radium is not as well studied as its stable lighter homologue barium, the two elements have very similar properties. Sony VAIO VGN-Z590NJB Battery
Their first two ionization energies are very similar: 509.3 and 979.0 kJ·mol?1 for radium and 502.9 and 965.2 kJ·mol?1 for barium. Such low figures yield both elements' high reactivity and the formation of the very stable Ra2+ ion and similar Ba2+.
Pure radium is a white, silvery, solid metal, melting at 700 °C (1292 °F) and boiling at 1737 °C (3159 °F), similar to barium. Radium has density of 5.5 g•cm3; Sony VAIO VGN-Z590UAB Battery
the radium-barium density ratio is comparable to the radium-barium atomic mass ratio, as these elements have very similar body-centered cubic structures.
Chemical characteristics and compounds
Radium is the heaviest alkaline earth metal; its chemical properties mostly resemble those of barium. Sony VAIO VGN-Z591U/B Battery
When exposed to air, radium reacts violently with it, forming radium nitride,[1] which causes blackening of this white metal. It exhibits only +2 oxidation state in solution. Radium ions do not form complexes easily, due to highly basic character of the ions. Most radium compounds coprecipitate with all barium, most strontium, and most lead compounds, and are ionic salts. Sony VAIO VGN-Z59G Battery
The radium ion is colorless, making radium salts white when freshly prepared, turning yellow and ultimately dark with age owing to self-decomposition from the alpha radiation. Compounds of radium flame red-purple and give a characteristic spectrum. Like otheralkaline earth metals, radium reacts violently with water and oil to form radium hydroxide and is slightly more volatile thanbarium, which leads to lesser solubility of radium compounds compared to those of corresponding barium ones. Sony VAIO VGN-Z620D Battery
Sony VAIO VGN-Z620N/B Battery
Because of its geologically short half-life and intense radioactivity, radium compounds are quite rare, occurring almost exclusively in uranium ores.
Radium chloride, radium bromide, radium hydroxide and radium nitrate are soluble in water, with solubilities slightly lower than those of barium analogs for bromide and chloride, and higher for nitrate. Sony VAIO VGN-Z650N/B Battery
Radium hydroxide is more soluble than hydroxides of other alkaline earth metals, actinium, and thorium, and more basic than barium hydroxide. It can be separated from these elements by their precipitation with ammonia.[1] Out of insoluble radium compounds, radium sulfate, radium chromate, radium iodate, radium carbonate, and radium tetrafluoroberyllate are characterized.[1] Sony VAIO VGN-Z670N/B Battery
Radium oxide, however, remains uncharacterized, despite the fact that other alkaline-earth metals' oxides are common compounds for the corresponding metals.
Radium has 25 different known isotopes, four of which are found in nature, with 226Ra being the most common. 223Ra, 224Ra,226Ra and 228Ra are all generated naturally in the decay of either uranium (U) or thorium (Th). Sony VAIO VGN-Z690CTO Battery
226Ra is a product of 238U decay, and is the longest-lived isotope of radium with a half-life of 1601 years; next longest is 228Ra, a product of 232Th breakdown, with a half-life of 5.75 years.[2]
Radium has no stable isotopes; however, four isotopes of radium are present in decay chains, having atomic masses of 223, 224, 226 and 228, all of which are present in trace amounts. Sony VAIO VGN-Z690NAX Battery
The most abundant and the longest-living one is radium-226, with a half-life of 1601 years. To date, 33 isotopes of radium have been synthesized, ranging in mass number from 202 to 234.
To date, at least 12 nuclear isomers have been reported; the most stable of them is radium-205m, with a half-life of between 130 and 230 milliseconds. Sony VAIO VGN-Z690PAB Battery
All ground states of isotopes from radium-205 to radium-214, and from radium-221 to radium-234, have longer ones.
Three other natural radioisotopes had received historical names in the early twentieth century: radium-223 was known asactinium X, radium-224 as thorium X and radium-228 as mesothorium I. Sony VAIO VGN-Z690PCB Battery
Radium-226 has given historical names to its decay products after the whole element, such as radium A for polonium-218.
Radioactivity
Radium is over one million times as radioactive as the same mass of uranium. Its decay occurs in at least seven stages; the successive main products have been studied and were called radium emanation or exradio (now identified as radon), radium A (polonium), radium B (lead), radium C (bismuth), etc. Sony VAIO VGN-Z690PDB Battery
Radon is a heavy gas, and the later products are solids. These products are themselves radioactive elements, each with an atomic weight a little lower than its predecessor.[3][4]
Radium loses about 1% of its activity in 25 years, being transformed into elements of lower atomic weight, with lead being the final product of disintegration.[5] Sony VAIO VGN-Z690PEB Battery
The SI unit of radioactivity is the becquerel (Bq), equal to one disintegration per second. The curie is a non-SI unit defined as that amount of radioactive material that has the same disintegration rate as 1 gram of radium-226 (3.7×1010 disintegrations per second, or 37 GBq).[6] Sony VAIO VGN-Z690PFB Battery
Radium metal maintains itself at a higher temperature than its surroundings because of the radiation it emits – alpha particles, beta particles, and gamma rays. More specifically, the alpha particles are produced by the radium decay, whereas the beta particles and gamma rays are produced by relatively short-half-life elements further down the decay chain.[7] Sony VAIO VGN-Z690YAD Battery
Occurrence
Radium is a decay product of uranium and is therefore found in all uranium-bearing ores. (One ton of pitchblende typically yields about one seventh of a gram of radium).[8] Radium was originally acquired from pitchblende ore from Joachimsthal, Bohemia, now located in the Czech Republic. Sony VAIO VGN-Z691Y/B Battery
Carnotite sands in Colorado provide some of the element, but richer ores are found in the Congo and the area of the Great Bear Lake and the Great Slave Lake of northwestern Canada.[9] Radium can also be extracted from the waste from nuclear reactors. Large radium-containing uranium deposits are located in Russia, Canada (the Northwest Territories), the United States (New Mexico, Utah and Colorado, for example) and Australia. Sony VAIO VGN-Z691Y/X Battery
Production
All radium occurring today is produced by the decay of heavier elements, being present in decay chains. Owing to such short half-lives of its isotopes, radium is notprimordial but trace. It cannot occur in large quantities due both to the fact that isotopes of radium have short half-lives and that parent nuclides have very long ones. Sony VAIO VGN-Z698Y/X Battery
Radium is found in tiny quantities in the uranium ore uraniniteand various other uranium minerals, and in even tinier quantities in thorium minerals.
The amounts produced were aways relatively small; for example, in 1918 13.6 g of radium were produced in the United states.[10] As of 1954, the total worldwide supply of purified radium amounted to about 5 pounds (2.3 kg).[11] Sony VAIO VGN-Z699JAB Battery
Radium (Latin radius, ray) was discovered by Marie Sk?odowska-Curie and her husband Pierre on December 21, 1898 in a uraninitesample. While studying the mineral, the Curies removed uranium from it and found that the remaining material was still radioactive. They then separated out a radioactive mixture consisting mostly of compounds of barium which gave a brilliant green flame color and crimson carmine spectral lines that had never been documented before. Sony VAIO VGN-Z70B Battery
The Curies announced their discovery to the French Academy of Sciences on 26 December 1898.[12] The naming of radium dates to circa 1899, from Frenchradium, formed in Modern Latin from radius (ray), called for its power of emitting energy in the form of rays.[13] Sony VAIO VGN-Z71JB Battery
Sony VAIO VGN-Z73FB Battery
In 1910, radium was isolated as a pure metal by Curie and André-Louis Debierne through the electrolysis of a pure radium chloridesolution by using a mercurycathode and distilling in an atmosphere of hydrogen gas.[14] The Curies' new element was first industrially produced in the beginning of the 20th century by Biraco, a subsidiary company of Union Minière du Haut Katanga(UMHK) in its Olen plant in Belgium. Sony VAIO VGN-Z790DKX Battery
UMHK offered to Marie Curie her first gram of radium. It gave historical names to the decay products of radium, such as radium A, B, C, etc., now known to be isotopes of other elements.
On 4 February 1936, radium E (bismuth-210) became the first radioactive element to be made synthetically in the United States. Sony VAIO VGN-Z790DMR Battery
Dr. John Jacob Livingood, at the radiation lab at University of California, Berkeley, was bombarding several elements with 5-MEV deuterons. He noted that irradiated bismuth emits fast electrons with a 5-day half-life, which matched the behavior of radium E.[15][16][17][18]
The common historical unit for radioactivity, the curie, is based on the radioactivity of 226Ra. Sony VAIO VGN-Z790DND Battery
Applications
Some of the few practical uses of radium are derived from its radioactive properties. More recently discovered radioisotopes, such as 60
Co and 137
Cs, are replacing radium in even these limited uses because several of these isotopes are more powerful emitters, safer to handle, and available in more concentrated form.[19][20]
When mixed with beryllium, it is a neutron source for physics experiments.[21] Sony VAIO VGN-Z820DB Battery
Historical uses
Radium was formerly used in self-luminous paints for watches, nuclear panels, aircraft switches, clocks, and instrument dials. A typical self-luminous watch that uses radium paint contains around 1 microgram of radium.[11] Sony VAIO VGN-Z820G/B Battery
In the mid-1920s, a lawsuit was filed by five dying "Radium Girl" dial painters who had painted radium-based luminous paint on the dials of watches and clocks. The dial painters' exposure to radium caused serious health effects which included sores, anemia, and bone cancer. This is because radium is treated as calcium by the body, and deposited in the bones, where radioactivity degrades marrow and can mutate bone cells. Sony VAIO VGN-Z890GLX Battery
During the litigation, it was determined that company scientists and management had taken considerable precautions to protect themselves from the effects of radiation, yet had not seen fit to protect their employees. Worse, for several years the companies had attempted to cover up the effects and avoid liability by insisting that the Radium Girls were instead suffering from syphilis. Sony VAIO VGN-Z890GMR Battery
This complete disregard for employee welfare had a significant impact on the formulation of occupational disease labor law.[22]
As a result of the lawsuit, the adverse effects of radioactivity became widely known, and radium-dial painters were instructed in proper safety precautions and provided with protective gear. Sony VAIO VGN-Z898H/X Battery
In particular, dial painters no longer shaped paint brushes by lip (which led to accidental ingestion of the radium salts). Radium was still used in dials as late as the 1960s, but there were no further injuries to dial painters. This further highlighted that the plight of the Radium Girls was completely preventable. Sony VAIO VGN-Z90FS Battery
After the 1960s, radium paint was first replaced with promethium paint, and later by tritium bottles which continue to be used today. Although the beta radiationfrom tritium is potentially dangerous if tritium is ingested, tritium has replaced radium in these applications.
Radium was once an additive in products such as toothpaste, hair creams, and even food items due to its supposed curative powers.[23] Sony VAIO VGN-Z90NS Battery
Such products soon fell out of vogue and were prohibited by authorities in many countries after it was discovered they could have serious adverse health effects. (See, for instance, Radithor orRevigator types of "Radium water" or "Standard Radium Solution for Drinking".) Sony VAIO VGN-Z90PS Battery
Spas featuring radium-rich water are still occasionally touted as beneficial, such as those in Misasa, Tottori, Japan. In the U.S., nasal radium irradiation was also administered to children to prevent middle-ear problems or enlarged tonsils from the late 1940s through the early 1970s.[24] Sony VAIO VGN-Z90S Battery
In 1909, the famous Rutherford experiment used radium as an alpha source to probe the atomic structure of gold. This experiment led to the Rutherford model of theatom and revolutionized the field of nuclear physics. Sony VAIO VGN-Z90US Battery
Radium (usually in the form of radium chloride) was used in medicine to produce radon gas which in turn was used as a cancertreatment; for example, several of these radon sources were used in Canada in the 1920s and 1930s.[25] The isotope 223
Ra is currently under investigation for use in medicine as a cancer treatment of bonemetastasis. Sony VAIO VGN-Z91DS Battery
Precautions
Radium is highly radioactive and its decay product, radon gas, is also radioactive. Since radium is chemically similar to calcium, it has the potential to cause great harm by replacing calcium in bones. Exposure to radium can cause cancer and other disorders, because radium and its decay product radon emit alpha particles upon their decay, which kill and mutate cells. Sony VAIO VGN-Z91JS Battery
The dangers of radium were apparent from the start. The first case of so-called "radium-dermatitis" was reported in 1900, only 2 years after the element's discovery. The French physicist Antoine Becquerel carried a small ampoule of radium around in his waistcoat pocket for 6 hours and reported that his skin became ulcerated. Sony VAIO VGN-Z91PS Battery
Marie Curie also had a similar incident in which she experimented with a tiny sample that she kept in contact with her skin for 10 hours and noted how an ulcer appeared, although not for several days.[26]Handling of radium has also been blamed for Curie's death due to aplastic anemia. Stored radium should be ventilated to prevent accumulation of radon. Sony VAIO VGN-Z91YS Battery
Emitted energy from the decay of radium also ionizes gases, affects photographic plates, and produces many other detrimental effects – to the extent that at the time of the Manhattan Project in 1944, the "tolerance dose" for workers was set at 0.1 microgram of ingested radium.
Actinium is a radioactive chemical element with the symbol Ac and atomic number 89, which was discovered in 1899. Sony VAIO VGN-Z92DS Battery
It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902. Actinium gave the name to the actinide series, a group of 15 similar elements between actinium and lawrencium in the periodic table. Sony VAIO VGN-Z92JS Battery
A soft, silvery-white radioactive metal, actinium reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that prevents further oxidation. As most lanthanides and actinides, actinium assumes oxidation state +3 in nearly all its chemical compounds. Sony VPCM12M1E/W Battery
Actinium is found only in traces in uranium ores as 227Ac isotope, which decays with ahalf-life of 21.772 years, predominantly emitting beta particles. One tonne of uranium ore contains about 0.2 milligrams of actinium. The close similarity of physical and chemical properties of actinium and lanthanum makes separation of actinium from the ore impractical. Sony VPCM13M1E/L Battery
Instead, the element is prepared, in milligram amounts, by the neutron irradiation of 226Ra in anuclear reactor. Owing to its scarcity, high price and radioactivity, actinium has no significant industrial use. Its current applications include a neutron source and an agent for radiation therapy targeting cancer cells in the body. Sony VPCM13M1E/P Battery
André-Louis Debierne, a French chemist, announced the discovery of a new element in 1899. He separated it from pitchblenderesidues left by Marie and Pierre Curie after they had extracted radium. In 1899, Debierne described the substance as similar to titanium[2] and (in 1900) as similar to thorium.[3] Sony VPCM13M1E/W Battery
Friedrich Oskar Giesel independently discovered actinium in 1902[4] as a substance being similar to lanthanum and called it "emanium" in 1904.[5] After a comparison of substances in 1904,[6]Debierne's name was retained because it had seniority.[7][8]
The stated history of the discovery of actinium remained uncertain for decades. Sony VAIO VGN-Z11MN/B Battery
Articles published in the 1970s[9] and later[10]suggest that Debierne's results published in 1904 conflict with those reported in 1899 and 1900. Whether Debierne and Giesel should share the merit of discovery or if Giesel alone should be credited is still under debate.[11]
The name actinium originates from the Ancient Greek aktis, aktinos (?????, ???????), meaning beam or ray.[12] Sony VAIO VGN-Z11VN/X Battery
Its symbol Ac is also used in abbreviations of other compounds that have nothing to do with actinium, such as acetyl, acetate[13] and sometimes acetaldehyde.[14]
Properties
Actinium is a soft, silvery-white,[15][16] radioactive, metallic element. Its estimated shear modulus is similar to that oflead.[17] Sony VAIO VGN-Z11WN/B Battery
Owing to its strong radioactivity, actinium glows in the dark with a pale blue light, which originates from the surrounding air ionized by the energetic particles emitted from actinium.[18] Actinium has similar chemical properties aslanthanum and other lanthanides, and therefore these elements are difficult to separate when extracting from uranium ores. Sony VAIO VGN-Z11XN/B Battery
Solvent extraction and ion chromatography are commonly used for the separation.[19]
The first element of the actinides, actinium gave the group its name, much as lanthanum has done for the lanthanides. The group of elements is more diverse than the lanthanides and therefore it was not until 1945 that Glenn T. Seaborg proposed the most significant change to Mendeleev's periodic table, by introducing the actinides.[20] Sony VAIO VGN-Z15 Battery
Actinium reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that prevents further oxidation.[15] As with most lanthanides and actinides, actinium exists in the oxidation state +3, and the Ac3+ ions are colorless in solutions.[21] The oxidation state +3 originates from the 6d17s2 electronic configuration of actinium, that is it easily donates 3 electrons assuming a stable closed-shell structure of the noble gas radon.[16] Sony VAIO VGN-Z15N Battery
The oxidation state +2 is only known for actinium dihydride.
Chemical compounds
Only a limited number of actinium compounds are known including AcF3, AcCl3, AcBr3, AcOF, AcOCl, AcOBr, Ac2S3, Ac2O3 and AcPO4. Except for AcPO4, they are all similar to the corresponding lanthanum compounds and contain actinium in the oxidation state +3. Sony VAIO VGN-Z17 Battery
In particular, the lattice constants of the analogous lanthanum and actinium compounds differ by only a few percent.[23]
Here a, b and c are lattice constants, No is space group number and Z is the number of formula units per unit cell. Density was not measured directly but calculated from the lattice parameters. Sony VAIO VGN-Z17N Battery
Oxides
Actinium oxide (Ac2O3) can be obtained by heating the hydroxide at 500 °C or the oxalate at 1100 °C, in vacuum. It crystal lattice is isotypic with the oxides of most trivalent rare-earth metals.[23] Sony VAIO VGN-Z19 Battery
Halides
Actinium trifluoride can be produced either in solution or in solid reaction. The former reaction is carried out at room temperature, by adding hydrofluoric acid to a solution containing actinium ions. In the latter method, actinium metal is treated with hydrogen fluoride vapors at 700 °C in an all-platinum setup. Sony VAIO VGN-Z19N Battery
Treating actinium trifluoride with ammonium hydroxide at 900–1000 °C yields oxyfluoride AcOF. Whereas lanthanum oxyfluoride can be easily obtained by burning lanthanum trifluoride in air at 800 °C for an hour, similar treatment of actinium trifluoride yields no AcOF and only results in melting of the initial product.[23][29] Sony VAIO VGN-Z21MN/B Battery
AcF3 + 2 NH3 + H2O ? AcOF + 2 NH4F
Actinium trichloride is obtained by reacting actinium hydroxide or oxalate with carbon tetrachloride vapors at temperatures above 960 °C. Similar to oxyfluoride, actinium oxychloride can be prepared by hydrolyzing actinium trichloride with ammonium hydroxide at 1000 °C. Sony VAIO VGN-Z21VN/X Battery
However, in contrast to the oxyfluoride, the oxychloride could well be synthesized by igniting a solution of actinium trichloride in hydrochloric acid with ammonia.[23]
Reaction of aluminium bromide and actinium oxide yields actinium tribromide:
Ac2O3 + 2 AlBr3 ? 2 AcBr3 + Al2O3
and treating it with ammonium hydroxide at 500 °C results in the oxybromide AcOBr.[23] Sony VAIO VGN-Z21WN/B Battery
Other compounds
Actinium hydride was obtained by reduction of actinium trichloride with potassium at 300 °C, and its structure was deduced by analogy with the corresponding LaH2hydride. The source of hydrogen in the reaction was uncertain.[30]
Mixing monosodium phosphate (NaH2PO4) with a solution of actinium in hydrochloric acid yields white-colored actinium phosphate hemihydrate (AcPO4·0.5H2O), Sony VAIO VGN-Z21XN Battery
and heating actinium oxalate with hydrogen sulfide vapors at 1400 °C for a few minutes results in a black actinium sulfide Ac2S3. It may possibly be produced by acting with a mixture of hydrogen sulfide and carbon disulfide on actinium oxide at 1000 °C.[23]
Naturally occurring actinium is composed of one radioactive isotope; 227Ac. Sony VAIO VGN-Z21ZN/X Battery
Thirty-six radioisotopes have been identified, 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 remaining radioactive isotopes have half-lives that are less than 10 hours and the majority of them have half-lives shorter than 1 minute. Sony VAIO VGN-Z25 Battery
The shortest-lived known isotope of actinium is 217Ac (half-life of 69 nanoseconds) which decays through alpha decayand electron capture. Actinium also has two meta states.[31]
Purified 227Ac comes into equilibrium with its decay products at the end of 185 days. It decays according to its 21.773-year half-life emitting mostly beta (98.8%) and some alpha particles (1.2%);[21] Sony VAIO VGN-Z25/B Battery
the successive decay products are part of the actinium series. Owing to the low available amounts, low energy of its beta particles (46 keV) and low intensity of alpha radiation, 227Ac is difficult to detect directly by its emission and it is therefore traced via its decay products.[21]The isotopes of actinium range in atomic weightfrom 206 u (206Ac) to 236 u (236Ac).[31] Sony VAIO VGN-Z25TN/B Battery
Occurrence and synthesis
Actinium is found only in traces in uranium ores as 227Ac – one tonne of ore contains about 0.2 milligrams of actinium.[32][33]These uranium ores sometimes contain lanthanum and other lanthanides. Sony VAIO VGN-Z26TN/B Battery
The actinium isotope 227Ac is a transient member of the actinium seriesdecay 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). Sony VAIO VGN-Z27 Battery
The low natural concentration, and the close similarity of physical and chemical properties to those of lanthanum and other lanthanides, which are always abundant in actinium-bearing ores, render separation of actinium from the ore impractical, and complete separation was never achieved.[23] Sony VAIO VGN-Z27/B Battery
Instead, actinium is prepared, in milligram amounts, by the neutron irradiation of 226Ra in a nuclear reactor.[33][34]
The reaction yield is about 2% of the radium weight. 227Ac can further capture neutrons resulting in small amounts of 228Ac. Sony VAIO VGN-Z27TN/X Battery
After the synthesis, actinium is separated from radium and from the products of decay and nuclear fusion, such as thorium, polonium, lead and bismuth. The extraction can be performed with thenoyltrifluoroacetone-benzene solution from an aqueous solution of the radiation products, and the selectivity to a certain element is achieved by adjusting the pH (to about 6.0 for actinium).[32] Sony VAIO VGN-Z29N Battery
An alternative procedure is anion exchange with an appropriate resin in nitric acid, which can result in a separation factor of 1,000,000 for radium and actinium vs. thorium in a two-stage process. Actinium can then be separated from radium, with a ratio of about 100, using a low cross-linking cation exchange resin and nitric acid as eluant.[35] Sony VAIO VGN-Z29N/X Battery
225Ac was first produced artificially at the Institute for Transuranium Elements (ITU) in Germany using a cyclotron and at St George Hospital in Sydney using a linacin 2000.[36] This rare isotope has potential applications in radiation therapy and is most efficiently produced by bombarding a radium-226 target with 20–30 MeVdeuterium ions. Sony VAIO VGN-Z31MN/B Battery
This reaction also yields 226Ac which however decays with a half-life of 29 hours and thus does not contaminate 225Ac.[37]
Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor in vacuum at a temperature between 1100 and 1300 °C. Sony VAIO VGN-Z31VN/X Battery
Higher temperatures resulted in evaporation of the product and lower ones lead to an incomplete transformation. Lithium was chosen among other alkali metals because its fluoride is most volatile.[12][15]
Applications
Owing to its scarcity, high price and radioactivity, actinium currently has no significant industrial use.[12] Sony VAIO VGN-Z31WN/B Battery
227Ac is highly radioactive and was therefore studied for use as an active element of radioisotope thermoelectric generators, for example in spacecraft. The oxide of227Ac pressed with beryllium is also an efficient neutron source with the activity exceeding that of the standard americium-beryllium and radium-beryllium pairs.[38] Sony VAIO VGN-Z31ZN/X Battery
In all those applications, 227Ac (a beta source) is merely a progenitor which generates alpha-emitting isotopes upon its decay. Beryllium captures alpha particles and emits neutrons owing to its large cross-section for the (?,n) nuclear reaction:
The 227AcBe neutron sources can be applied in a neutron probe – a standard device for measuring the quantity of water present in soil, Sony VAIO VGN-Z35 Battery
as well as moisture/density for quality control in highway construction.[39][40] Such probes are also used in well logging applications, in neutron radiography, tomography and other radiochemical investigations.[41]
225Ac is applied in medicine to produce 213Bi in a reusable generator[35] or can be used alone as an agent for radiation therapy, in particular targeted alpha therapy (TAT). Sony VAIO VGN-Z35/B Battery
This isotope has a half-life of 10 days that makes it much more suitable for radiation therapy than 213Bi (half-life 46 minutes). Not only 225Ac itself, but also its decay products emit alpha particles which kill cancer cells in the body. The major difficulty with application of 225Ac was that intravenous injection of simple actinium complexes resulted in their accumulation in the bones and liver for a period of tens of years. Sony VAIO VGN-Z35TN/B Battery
As a result, after the cancer cells were quickly killed by alpha particles from 225Ac, the radiation from the actinium and its decay products might induce new mutations. To solve this problem, 225Ac was bound to a chelating agent, such as citrate, ethylenediaminetetraacetic acid (EDTA) or diethylene triamine pentaacetic acid (DTPA). Sony VAIO VGN-Z36GD Battery
This reduced actinium accumulation in the bones, but the excretion from the body remained slow. Much better results were obtained with such chelating agents as HEHA[42] or DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) coupled to trastuzumab, a monoclonal antibody that interferes with the HER2/neu receptor. Sony VAIO VGN-Z36GD/B Battery
The latter delivery combination was tested on mice and proved to be effective against leukemia, lymphoma,breast, ovarian, neuroblastoma and prostate cancers.[43][44][45]
The medium half-life of 227Ac (21.77 years) makes it very convenient radioactive isotope in modeling the slow vertical mixing of oceanic waters. Sony VAIO VGN-Z36GD/J Battery
The associated processes cannot be studied with the required accuracy by direct measurements of current velocities (of the order 50 meters per year). However, evaluation of the concentration depth-profiles for different isotopes allows estimating the mixing rates. The physics behind this method is as follows: oceanic waters contain homogeneously dispersed 235U. Sony VAIO VGN-Z36TD/B Battery
Its decay product, 231Pa, gradually precipitates to the bottom, so that its concentration first increases with depth and then stays nearly constant. 231Pa decays to 227Ac; however, the concentration of the latter isotope does not follow the 231Pa depth profile, but instead increases toward the sea bottom. Sony VAIO VGN-Z36TD/J Battery
This occurs because of the mixing processes which raise some additional 227Ac from the sea bottom. Thus analysis of both 231Pa and 227Ac depth profiles allows to model the mixing behavior.[46][47] Sony VAIO VGN-Z37D Battery
Precautions
227Ac is highly radioactive and experiments with it are carried out in a specially designed laboratory equipped with a glove box and radiation shielding. When actinium trichloride is administered intravenously to rats, about 33% of actinium is deposited into the bones and 50% into the liver. Sony VAIO VPCZ114GX/S Battery
Its toxicity is comparable, but slightly lower than that of americium and plutonium.
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder. Sony VAIO VPCZ115 Battery
In nature, virtually all thorium is found thorium-232, and it decays by emitting an alpha particle, and has a half-life of about 14.05 billion years (other, trace-level isotopes of thorium are short-lived intermediates of decay chains). It is estimated to be about three times more abundant than uranium in the Earth's crust and is a by-product of the extraction ofrare earths from monazitesands. Sony VAIO VPCZ115FC/B Battery
Thorium was formerly used commonly as (for example) the light source in gas mantles and as an alloying material, but these applications have declined due to concerns about its radioactivity.
The molten-salt reactor experiment conducted in the United States from 1964 to 1969 used thorium-232 to breed uranium-233; most of the test reactors were closed down. Sony VAIO VPCZ115FC/S Battery
Countries like Russia, India and China now have plans to use thorium for their nuclear power for various reasons, including its safety benefits, its high absolute abundance and relative abundance compared to uranium.
Physical properties
Pure thorium is a silvery-white metal which is air-stable and retains its luster for several months. Sony VAIO VPCZ116 Battery
When contaminated with the oxide, thorium slowly tarnishes in air, becoming gray and finally black. The physical properties of thorium are greatly influenced by the degree of contamination with the oxide.[2]The purest specimens often contain several tenths of a percent of the oxide. Sony VAIO VPCZ116GX/S Battery
Pure thorium is soft, veryductile, and can be cold-rolled, swaged, and drawn. Thorium is dimorphic, changing at 1360 °C from aface-centered cubic to a body-centered cubic structure; a body-centered tetragonal lattice form exists at high pressure with impurities driving the exact transition temperatures and pressures.[2] Sony VAIO VPCZ117 Battery
Powdered thorium metal is often pyrophoric and requires careful handling. When heated in air, thorium metalturnings ignite and burn brilliantly with a white light. Thorium has one of the largest liquid temperature ranges of any element, with 2946 °C between the melting point and boiling point.[3] Thorium metal is paramagnetic with a ground state of 6d27s2.[2] Sony VAIO VPCZ117FC/B Battery
Chemical properties
Thorium is slowly attacked by water, but does not dissolve readily in most common acids, excepthydrochloric acid.[3] It dissolves in concentrated nitric acid containing a small amount of catalytic fluoride ion.[4] Sony VAIO VPCZ118 Battery
Compounds
Thorium compounds are stable in the +4 oxidation state.[5]
Thorium dioxide has the highest melting point (3300 °C) of all oxides.[6]
Thorium(IV) nitrate and thorium(IV) fluoride are known in their hydrated forms: Th(NO3)4·4H2O and ThF4·4H2O, respectively.[5]Thorium(IV) carbonate, Th(CO3)2, is also known.[5] Sony VAIO VPCZ118GC/B Battery
When treated with potassium fluoride and hydrofluoric acid, Th4+ forms the complex anion ThF2?
6, which precipitates as an insoluble salt, K2ThF6.[4]
Thorium(IV) hydroxide, Th(OH)4, is highly insoluble in water, and is not amphoteric. The peroxide of thorium is rare in being an insoluble solid. Sony VAIO VPCZ118GX/S Battery
This property can be utilized to separate thorium from other ions in solution.[4]
In the presence of phosphate anions, Th4+ forms precipitates of various compositions, which are insoluble in water and acid solutions.[4]
Thorium monoxide has recently been produced through laser ablation of thorium in the presence of oxygen.[7] Sony VAIO VPCZ119 Battery
Twenty-seven radioisotopes have been characterized, with a range in atomic weight from 210 u (210Th) to 236 u (236Th).[8] The most stable isotopes are:
- 232Th with a half-life of 14.05 billion years, it represents all but a trace of naturally occurring thorium.
230Th with a half-life of 75,380 years. Occurs as the daughter product of 238U decay. Sony VAIO VPCZ119FJ/S Battery
- 229Th with a half-life of 7340 years. It has a nuclear isomer (or metastable state) with a remarkably low excitation energy of 7.6 eV.[9]
- 228Th with a half-life of 1.92 years.
All of the remaining radioactive isotopes have half-lives that are less than thirty days and the majority of these have half-lives that are less than ten minutes. Sony VAIO VPCZ119GC/X Battery
Thorium
Thorium is a component of the magnesium alloy called Mag-Thor, used in aircraft engines and imparting high strengthand creepresistance at elevated temperatures.[10][11] Thoriated magnesium was used to build the CIM-10 Bomarc missile, although concerns about radioactivity have resulted in several missiles being removed from public display. Sony VAIO VPCZ119L Battery
Thorium is also used as an alloying agent in gas tungsten arc welding (GTAW) to increase the melting temperature of tungsten electrodes and improve arc stability.[12] The electrodes labeled EWTH-1 contain 1% thorium, while the EWTH-2 contain 2%.[13]In electronic equipment, thorium coating of tungsten wire improves the electron emission of heated cathodes.[3] Sony VAIO VPCZ119R/B Battery
Thorium is a very effective radiation shield, although it has not been used for this purpose as much as lead or depleted uranium. Uranium-thorium age dating has been used to date hominid fossils,[3] seabeds, and mountain ranges.[14] Environmental concerns related to radioactivity led to a sharp decrease in demand for nonnuclear uses of thorium in the 2000s.[14] Sony VAIO VPCZ119R/S Battery
Thorium compounds
Thorium dioxide (ThO2) and thorium nitrate (Th(NO3)4) were used in mantles of portable gas lights, including natural gas lamps, oil lamps and camping lights. These mantles glow with an intense white light (unrelated to radioactivity) when heated in a gas flame, and its color could be shifted to yellow by addition of cerium.[11] Sony VAIO VPCZ11AFJ Battery
Thorium dioxide is a material for heat-resistant ceramics, e.g., for high-temperature laboratory crucibles.[12] When added to glass, it helps increase refractive index and decrease dispersion. Such glass finds application in high-quality lenses for cameras and scientific instruments.[3] Sony VAIO VPCZ11AGJ Battery
The radiation from these lenses can self-darken (yellow) them over a period of years and degrade film, but the health risks are minimal.[15] Yellowed lenses may be restored to their original colorless state with lengthy exposure to intense UV light.
Thorium dioxide was used to control the grain size of tungsten metal used for spirals of electric lamps. Sony VAIO VPCZ11AVJ Battery
Thoriated tungsten elements are found in the filaments ofmagnetron tubes. Thorium is added because of its ability to emit electrons at relatively low temperatures when heated in vacuum. Those tubes generate microwavefrequencies and are applied in microwave ovens and radars.[11] Sony VAIO VPCZ11CGX/X Battery
Thorium dioxide has been used as a catalyst in the conversion of ammonia to nitric acid,[12] in petroleum cracking and in producing sulfuric acid. It is the active ingredient of Thorotrast, which was used as part of X-ray diagnostics. This use has been abandoned due to the carcinogenic nature of Thorotrast.[3] Sony VAIO VPCZ11DGX/SJ Battery
Despite its radioactivity, thorium fluoride (ThF4) is used as an antireflection material in multilayered optical coatings. It has excellent optical transparency in the range 0.35–12 µm, and its radiation is primarily due to alpha particles, which can be easily stopped by a thin cover layer of another material.[16] Sony VAIO VPCZ11FHX/XQ Battery
Thorium fluoride was also used in manufacturing carbon arc lamps, which provided high-intensity illumination for movie projectors and search lights.[11]
Benefits and challenges
Thorium can be used as fuel in a nuclear reactor, and it is a fertile material, which allows it to be used to produce nuclear fuel in a breeder reactor. Sony VAIO VPCZ11V9R/B Battery
In 1997, the U.S. Energy Department underwrote research into thorium fuel, and research was also begun in 1996 by the International Atomic Energy Agency (IAEA), to study the use of thorium reactors. Nuclear scientist Alvin Radkowsky of Tel Aviv University in Israel founded a consortium to develop thorium reactors, which included other companies: Sony VAIO VPCZ11X9E/B Battery
Raytheon Nuclear Inc., Brookhaven National Laboratory, and the Kurchatov Institute in Moscow.[17] Radkowsky was chief scientist in the U.S. nuclear submarine program directed by Admiral Hyman Rickover and later headed the design team which built the USA's first civilian nuclear power plant at Shippingport, Pennsylvania, which was a scaled-up version of the first naval reactor.[17] Sony VAIO VPCZ11Z9E/B Battery
Some countries, including India, are now investing in research to build thorium-based nuclear reactors. A 2005 report by the International Atomic Energy Agency discusses potential benefits along with the challenges of thorium reactors.[18] India has also made thorium-based nuclear reactors a priority with its focus on developing fast breeder technology.[19][20] Sony VAIO VPCZ125GX/S Battery
Some benefits of thorium fuel when compared with uranium were summarized as follows:[21]
- Weapons-grade fissionable material (233U) is harder to retrieve safely and clandestinely from a thorium reactor;
Thorium produces 10 to 10,000 times less long-lived radioactive waste; Sony VAIO VPCZ127FC Battery
The fissionable thorium cycle uses 100% of the isotope as coming out of the ground, which does not require enrichment, whereas the fissile uranium cycle depends on the only 0.7% fissile U-235 of the natural uranium. The same cycle could also use the fissionable U-238 component of the natural uranium, and also contained in the depleted reactor fuel; Sony VAIO VPCZ128GC Battery
- Thorium cannot sustain a nuclear chain reaction without priming [22] so fission stops by default.
However, when used in a breeder like reactor, unlike uranium-based breeder reactors, thorium requires irradiation and reprocessing before the above-noted advantages of thorium-232 can be realized, which makes thorium fuels initially more expensive than uranium fuels.[14] Sony VAIO VPCZ12M9E/B Battery
But experts note that "the second thorium reactor may activate a third thorium reactor. This could continue in a chain of reactors for a millennium if we so choose." They add that because of thorium's abundance, it will not be exhausted in 1,000 years.[23]
The Thorium Energy Alliance (TEA), an educational advocacy organization, emphasizes that "there is enough thorium in the United States alone to power the country at its current energy level for over 1,000 years."[24] Sony VAIO VPCZ13M9E/B Battery
Thorium energy fuel cycle
Although not fissile itself, 232Th will absorb slow neutrons to produce, after two beta decays, 233U, which is fissile.[14] Hence, like 238U, it is fertile. Also, preparation of thorium fuel does not require isotopic separation. Sony VAIO VPCZ13V9E/X Battery
The thorium fuel cycle creates 233U, which, if separated from the reactor's fuel, can be used for making nuclear weapons. This is why a liquid-fuel cycle (e.g.,Molten Salt Reactor or MSR) is preferred — only a limited amount of 233U ever exists in the reactor and its heat-transfer systems, preventing any access to weapons material; Sony VAIO VPCZ13Z9E/X Battery
however the neutrons produced by the reactor can be absorbed by a thorium or uranium blanket and fissile 233U or 239Pu produced. Also, the 233U could be continuously extracted from the molten fuel as the reactor is running. Neutrons from the decay of uranium-233 can be fed back into the fuel cycle to start the cycle again.[14] Sony VAIO VPCZZZHJ Battery
The neutron flux from spontaneous fission of 233U is negligible. 233U can thus be used easily in a simple gun-type nuclear bomb design.[25] In 1977, a light-water reactor at the Shippingport Atomic Power Station was used to establish a 232Th-233U fuel cycle. The reactor worked until its decommissioning in 1982.[26][27][28] Sony VAIO VPZ117 Battery
Thorium can be and has been used to power nuclear energy plants using both the modified traditional Generation III reactor design and prototype Generation IV reactordesigns. The use of thorium as an alternative fuel is one innovation being explored by the International Project on Innovative Nuclear Reactors and Fuel Cycles (INPRO),[29] conducted by the International Atomic Energy Agency (IAEA). Sony VAIO VPZ118 Battery
Unlike its use in MSRs, when using solid thorium in modified light water reactor (LWR) problems include: the undeveloped technology for fuel fabrication; in traditional, once-through LWR designs potential problems in recycling thorium due to highly radioactive 228Th; Sony VAIO VPZ119 Battery
some weapons proliferation risk due to production of233U; and the technical problems (not yet satisfactorily solved) in reprocessing. Much development work is still required before the thorium fuel cycle can be commercialized for use in LWR. The effort required has not seemed worth it while abundant uranium is available, Sony VPCM11M1E/B Battery
but geopolitical forces (e.g. India looking for indigenous fuel) as well as uranium production issues, proliferation concerns, and concerns about the disposal/storage of radioactive waste are starting to work in its favor.[citation needed]
Commercial nuclear power station
India's Kakrapar-1 reactor is the world's first reactor which uses thorium rather than depleted uranium to achieve power flattening across the reactor core.[30] Sony VPCM11M1E/W Battery
India, which has about 25% of the world's thorium reserves, is developing a 300 MW prototype of a thorium-based Advanced Heavy Water Reactor (AHWR). The prototype is expected to be fully operational by 2011, after which five more reactors will be constructed.[31] Sony VPCM12M1E/L Battery
Considered to be a global leader in thorium-based fuel, India's new thorium reactor is a fast-breeder reactor and uses a plutonium core rather than an accelerator to produce neutrons. As accelerator-based systems can operate at sub-criticality they could be developed too, but that would require more research.[32] India currently envisages meeting 30% of its electricity demand through thorium-based reactors by 2050.[33] Sony VPCM12M1E/P Battery
Existing thorium energy projects
The German THTR-300 was the first commercial power station powered almost entirely with Thorium. India's 300 MWe AHWR CANDU type reactor will begin construction in 2011. The design envisages a start up with reactor grade plutonium which will breed U-233 from Th-232. After that the input will only be thorium for the rest of the reactor's design life.[34] Sony VAIO VPCW215AG/L Battery
The primary fuel of the HT3R Project near Odessa, Texas, USA will be ceramic-coated thorium beads. The earliest date the reactor will become operational in 2015.[35]
Best results occur with molten salt reactors (MSRs), such as ORNL's liquid fluoride thorium reactor (LFTR), Sony VAIO VPCW217JC Battery
which have built-in negative-feedback reaction rates, due to salt expansion and thus reactor throttling via load. This is a great safety advantage, since no emergency cooling system is needed, which is both expensive and adds thermal inefficiency. In fact, an MSR was chosen as the base design for the 1960s DoD nuclear aircraft largely because of its great safety advantages, even under aircraft maneuvering. Sony VAIO VPCW217JC/L Battery
In the basic design, an MSR generates heat at higher temperatures, continuously, and without refuelling shutdowns, so it can provide hot air to a more efficient (Brayton Cycle) turbine. An MSR run this way is about 30% better in thermal efficiency than common thermal plants, whether combustive or traditional solid-fuelled nuclear.[24] Sony VAIO VPCW217JC/P Battery
In 2010, Congressman Joe Sestak added funding for research and development of a destroyer-sized reactor using thorium.[36]
CANDU reactors of Atomic Energy Canada Limited are capable of using thorium as a fuel source. Sony VAIO VPCW217JC/T Battery
At the 2011 annual conference of the Chinese Academy of Sciences it was announced that "China has initiated a research and development project in thorium molten-salt reactor technology."
Projects combining uranium and thorium
Fort St. Vrain Generating Station, a demo HTGR in Colorado, USA, operating from 1977 until 1992, employed enriched uranium fuel that also contained thorium. Sony VAIO VPCW217JC/W Battery
This resulted in high fuel efficiency because the thorium was converted to uranium and then burnt.
Swedish chemist Jöns Jakob Berzelius analyzed a mineral from the Falun district in 1828 and determined that it contained a new element, which he named thorium afterThor, the Norse god of thunder.[12] Sony VAIO VPCW218JC Battery
Analysis 10 years later found that the mineral was xenotime (YP). Morten Thrane Esmark found a black mineral on Løvøy Island,Norway and gave a sample to his father Jens Esmark, a noted mineralogist. The elder Esmark was not able to identify it and sent a sample to Berzelius for examination in 1828.[41][42] Sony VAIO VPCW218JC/L Battery
Berzelius analyzed it and gave it the same name as the misidentified sample of xenotime. The metal had no practical uses until Carl Auer von Welsbachinvented the gas mantle in 1885.[12]
Thorium was first observed to be radioactive in 1898, independently, by Polish-French physicist Marie Curie and German chemist Gerhard Carl Schmidt.[ Sony VAIO VPCW218JC/P Battery
Between 1900 and 1903, Ernest Rutherford and Frederick Soddy showed how thorium decayed at a fixed rate over time into a series of other elements. This observation led to the identification of half-life as one of the outcomes of the alpha particle experiments that led to their disintegration theory of radioactivity.[46] Sony VAIO VPCW218JC/T Battery
The crystal bar process (or "iodide process") was discovered by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925 to produce high-purity metallic thorium.[47]
The name ionium was given early in the study of radioactive elements to the 230Th isotope produced in the decay chain of 238Ubefore it was realized that ionium and thorium were chemically identical. The symbol Io was used for this supposed element. Sony VAIO VPCW218JC/W Battery
Occurrence
Thorium is found in small amounts in most rocks and soils; it is three times more abundant than tin in the Earth's crust and is about as common as lead.[48] Soil commonly contains an average of around 12 parts per million (ppm) of thorium. Thorium occurs in several minerals including thorite (ThSiO4), thorianite (ThO2 + UO2) and monazite. Sony VAIO VPCW219AJ/L Battery
Thorianite is a rare mineral and may contain up to about 12% thorium oxide. Monzonite contains 2.5% thorium, allanite has 0.1 to 2% thorium and zircon can have up to 0.4% thorium.[49] Thorium-containing minerals occur on all continents. Thorium is several times more abundant in Earth's crust than all isotopes of uranium combined and thorium-232 is several hundred times more abundant than uranium-235.[14] Sony VAIO VPCW219AJ/P Battery
232Th decays very slowly (its half-life is comparable to the age of the universe) but other thorium isotopes occur in the thorium and uranium decay chains. Most of these are short-lived and hence much more radioactive than 232Th, though on a mass basis they are negligible. Sony VAIO VPCW219AJ/W Battery
Thorium extraction
Thorium has been extracted chiefly from monazite through a complex multi-stage process. The monazite sand is dissolved in hot concentrated sulfuric acid (H2SO4). Thorium is extracted as an insoluble residue into an organic phase containing an amine. Sony VAIO VPCW21AAJ Battery
Next it is separated or stripped using an ion such as nitrate, chloride, hydroxide, or carbonate, returning the thorium to an aqueous phase. Finally, the thorium is precipitated and collected.[52]
Several methods are available for producing thorium metal: it can be obtained by reducing thorium oxide with calcium, Sony VAIO VPCW21AKJ Battery
by electrolysis of anhydrous thorium chloride in a fused mixture of sodium and potassium chlorides, by calcium reduction of thorium tetrachloride mixed with anhydrous zinc chloride, and by reduction of thorium tetrachloride with an alkali metal.[3]
Reserves
Present knowledge of the distribution of thorium resources is poor because of the relatively low-key exploration efforts arising out of insignificant demand.[53] Sony VAIO VPCW21AVJ Battery
There are two sets of estimates that define world thorium reserves, one set by the US Geological Survey (USGS) and the other supported by reports from the OECD and the International Atomic Energy Agency (the IAEA). Under the USGS estimate, USA, Australia and India have particularly large reserves of thorium. Sony VAIO VPCY115FGS Battery
Both the IAEA and OECD appear to conclude that India may actually possess the lion's share of world's thorium deposits. The Government of India's estimate puts the reserve at 846,477 tonnes.[54] The logic for this assessment is as follows.
OECD assessment
India and Australia are believed to possess about 300,000 tonnes each; i.e. each country possessing 25% of the world's thorium reserves.[55] Sony VAIO VPCY115FX/BI Battery
However, in the OECD reports, estimates of Australia's Reasonably Assured Reserves (RAR) of thorium indicate only 19,000 tonnes and not 300,000 tonnes as indicated by USGS. The two sources vary wildly for countries such as Brazil, Turkey, and Australia. However, both reports appear to show some consistency with respect to India's thorium reserve figures, with 290,000 tonnes (USGS) and 319,000 tonnes (OECD/IAEA). Sony VAIO VPCY115FXBI Battery
IAEA assessment
The IAEA's 2005 report estimates India's reasonably assured reserves of thorium at 319,000 tonnes, but mentions recent reports of India's reserves at 650,000 tonnes.[56]
The prevailing estimate of the economically available thorium reserves comes from the US Geological Survey, Mineral Commodity Summaries (1996–2010): Sony VAIO VPCY118EC Battery
Note: The OECD/NEA report notes that the estimates (that the Australian figures are based on) are subjective, due to the variability in the quality of the data, a lot of which is old and incomplete.[58] Adding to the confusion are subjective claims made by the Australian government (in 2009, through its "Geoscience" department) that combine the reasonably assured reserves (RAR) estimates with "inferred" data (i.e. subjective guesses). Sony VAIO VPCY118GX/BI Battery
This strange combined figure of RAR and "guessed" reserves yields a figure, published by the Australian government, of 489,000 tonnes.[58] However, using the same criteria for Brazil or India would yield reserve figures of between 600,000 to 1,300,000 tonnes for Brazil and between 300,000 to 600,000 tonnes for India. Sony VAIO VPCY119FJ/S Battery
Irrespective of isolated claims by the Australian government, the most credible third-party and multi-lateral reports, those of the OECD/IAEA and the USGS, consistently report high thorium reserves for India while not doing the same for Australia.
Another estimate of reasonably assured reserves (RAR) and estimated additional reserves (EAR) of thorium comes from OECD/NEA, Nuclear Energy, "Trends in Nuclear Fuel Cycle", Paris, France (2001):[59] Sony VAIO VPCY11AFJ Battery
Dangers and biological roles
Powdered thorium metal is pyrophoric and will often ignite spontaneously in air. Natural thorium decays very slowly compared to many other radioactive materials, and the alpha radiation emitted cannot penetrate human skin meaning owning and handling small amounts of thorium, such as a gas mantle, is considered safe. Sony VAIO VPCY11AGJ Battery
Exposure to an aerosol of thorium can lead to increased risk of cancersof the lung, pancreas, and blood, as lungs and other internal organs can be penetrated by alpha radiation. Exposure to thorium internally leads to increased risk of liver diseases. Sony VAIO VPCY11AHJ Battery,Sony VAIO VPCY11AVJ Battery,Sony VAIO VPCY11M1E/S Battery,Sony VAIO VPCY11S1E Battery,Sony VAIO VPCY11V9E/S Battery
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