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Rarest Element, Astatine, Has Key Property Measured For First Time

Rarest Element On Earth Spotlighted In New Study
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By: Clara Moskowitz, LiveScience Senior Writer
Published: 05/16/2013 03:32 PM EDT on LiveScience

A fundamental property of the rarest element on Earth, astatine, has been discovered for the first time, scientists say.

Astatine occurs naturally; however, scientists estimate much less than an ounce in total exists worldwide. For a long time, the characteristics of this elusive element were a mystery, but physicists at the CERN physics laboratory in Switzerland have now measured its ionization potential — the amount of energy needed to remove one electron from an atom of astatine, turning it into an ion or a charged particle.

The measurement fills in a missing piece of the periodic table of elements, because astatine was the last naturally occurring element for which this property was unknown. Astatine, which has 85 protons and 85 electrons per atom, is radioactive, and half of its most stable version decays in just 8.1 hours, a time called half-life. In 1953, Isaac Asimov estimated the worldwide total of astatine in nature was 0.002 ounces (0.07 grams). [Graphic: Nature's Tiniest Particles Explained]

To measure astatine's ionization potential, physicists at CERN's ISOLDE (Isotope Separator On Line-Detector) Radioactive Ion Beam facility created artificial isotopes of astatine (atoms with different numbers of neutrons than those occurring in nature) by shooting beams of energetic protons at a target of uranium (which has 92 protons and electrons). The collisions created a shower of new particles, some of which were astatine.

The physicists then shined laser beams of varying wavelengths at the atoms to ionize them. By isolating the astatine ions, and checking which wavelength of laser had created them, the researchers determined astatine's ionization potential to be 9.31751 electronvolts (the ionization potential of hydrogen, for example, is 13.6 electronvolts).

The value will serve as a benchmark for studying exotic superheavy elements, which don't occur naturally, but can be created at specialized labs. For example, researchers want to compare the properties of astatine with those of the newly discovered element 117, first created at Russia's Joint Institute for Nuclear Research (JINR) in 2010. This element, the second-heaviest ever created, is a homologue of astatine, meaning that it sits right below astatine on the periodic table and likely shares similar properties.

"In-source laser spectroscopy today is a most sensitive method to study atomic properties of exotic short-lived isotopes," Valentin Fedosseev, team leader of ISOLDE's resonance ionization laser ion source, said in a statement. "It is well-suited to explore the spectra of artificially produced elements, like the superheavy ones. The success in this study of astatine has added confidence for similar projects started recently at GANIL, France, and at JINR, Russia." (GANIL stands for Grand Accélérateur National d'Ions Lourds, or the Large Heavy Ion National Accelerator.)

The new discovery could also help scientists develop medical applications for artificial astatine, which might be useful in radiotherapy treatments for cancer called alpha therapy.

"None of the many short-lived isotopes used in medicine exist in nature; they have to be artificially produced by nuclear reactions," said Bruce Marsh, a resonance ionization laser ion source team member. "The possible medical isotopes of astatine are not so different in this respect. What is different about astatine is that its scarcity in nature makes it difficult to study by experiment, which is why this measurement of one of the fundamental properties is a significant achievement."

Follow Clara Moskowitz on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on LiveScience.com.

Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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Before You Go

The Most Bizarre Scientific Experiments
Caffeine For Imprisoned Twins(01 of05)
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In the late 18th century, King Gustavus III of Sweden was rumored to have carried out a strange experiment to determine the harmful health effects of coffee. Two identical twins who had been condemned to death had their sentences commuted to life in prison on the condition that one would drink three pots of coffee per day, and the other three pots of tea, for the rest of their lives. The only problem was that the doctors assigned to monitor the cases died before either of the patients did, their observations lost--as the story goes, the tea drinker died first, and there's no record of the coffee-drinker's death. The experiment proved nothing, suffering from a lack of rigor (to say the least).Source: Uppsala University, "Coffee - rat poison or miracle medicine?"
Simulated Anthrax On The Subway(02 of05)
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In June 1966, the U.S. Army's Special Operations Division secretly dispersed harmless bacteria in the New York Subway system to model the effects of an outbreak of more harmful germs. According to Army reports, "Test results show that a large portion of the working population of New York City would be exposed to disease if one or more pathogenic agents were disseminated covertly in several subway lines at a period of peak traffic."Source: Deadly Cultures: Biological Warfare Since 1945. Wheelis, Rózsa, and Dando. Harvard University Press, 2006. (credit:Billy Hathorn / Wikimedia Commons)
Weaponized Fleas In The Desert(03 of05)
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Operation Big Itch, 1954, was an attempt to discover the potential of weaponized fleas. The operation, part of the Cold War-era United States biological weapons program, took place at Dugway Proving Ground in Utah.According to "Using the flea as weapon," an article in the Army Chemical Review, "In the United States, the plague flea concept was competing against the use of mosquitoes, flies, ticks, and lice. Of these concepts, the United States put most of its energies behind weaponizing yellow fever in combination with the Aedes aegypti mosquito."
Food Through A Hole In The Stomach(04 of05)
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U.S. Army Surgeon William Beaumont (above) found an extraordinary patient in Alexis St. Martin, a Canadian trapper who was injured in a hunting accident and left with a hole in his belly that led directly into his stomach. Beaumont attached a string to various foods, including oysters and rare roast beef, and introduced them into the wound to observe the rates of digestion. Despite the unorthodox techniques, this research would later lead to the discovery of the importance of stomach acid in digestion, earning Beaumont the epithet "father of gastric physiology." Source: Experiments and observations on the gastric juice, and the physiology of digestion. Beaumont, Martin and Combe. Maclachlan & Stewart, 1838
Candy For Mental Patients(05 of05)
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In 1945, Sweden's new National Dental Service commissioned research, now known as the Vipeholm experiments, in which researchers gave subjects large amounts of sticky sugary candy in order to study the development of cavities. This might not have been so controversial, except that the subjects couldn't give consent to their participation:"The use of mentally handicapped subjects was criticized in the Swedish press and all studies on mentally handicapped individuals were stopped in 1954," according to Topics In Dental Biochemistry by Mark Levine (Springer, 2010). (credit:Gila Brand / Wikimedia Commons)
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