POLONIUM

CHERYL HOGUE, C&EN WASHINGTON

POLONIUM AT A GLANCE
Name: Named for Poland, the native country of scientist Marie Curie.
Atomic mass: (209).
History: Discovered by Marie and Pierre Curie in 1898 while studying a material called pitchblende.
Occurrence: Formed chiefly through the decay of radioactive uranium and thorium.
Appearance: Silvery metal.
Behavior: Extremely toxic and radioactive. About half of a sample will evaporate within two days if kept at 55 ºC. Polonium dissolves readily in dilute acids but is only slightly soluble in alkalis.
Uses: Used in nuclear batteries, antistatic agents, and film cleaners. It is also used as a neutron source, as a lightweight heat supply for space satellites, and as a source of -radiation for research.
Were these scientists making a Polish joke? I was an adolescent with my nose deep into a book on heroes and heroines, soaking up a story about Marie Curie. I was learning how this extremely smart scientist spent hours in mind-numbing labor stirring a boiling concoction as she processed pitchblende in a quest to figure out exactly what in this uranium ore made it more radioactive than uranium itself. On July 18, 1898, she and husband Pierre discovered a new element. They named it polonium, after Marie's homeland, Poland.

"Poland!" I shouted to my book. Of all the nations in the world, how could the Curies name an element after a country whose citizens were the butt of all the jokes making the rounds at my school? Wasn't her name Marie? So very French! And did she not earn her degrees, work, marry, and die in France?

But I soon learned how much Marie, born Marya Sklodowska, loved her native country and yearned to return there, though she never did move back. A crack appeared in my adolescent outlook on life, allowing the thought to slip in that just maybe there was more to Poland than jokes.

Polonium, Marie's dear polonium, number 84 on the periodic chart, was the first element discovered via its radioactivity. In their work with pitchblende, the Curies next identified radium (named after the Latin word for ray). In 1899, André Debierne, a colleague of the Curies, teased out a third radioactive element from pitchblende--actinium.

Though polonium was the first highly radioactive element the Curies identified, radium became the star of their work. Marie, writing in December 1904, explained why: "Polonium, when it has just been extracted from pitchblende, is as active as radium, but its radioactivity slowly disappears." We know now that polonium's most stable isotope has a half-life of 138.39 days compared with the 1,620 years of radium's longest lived isotope. The Curies never isolated polonium, which is formed as one of the decay products of radium.

Though the scientific community was at first doubtful about the existence of polonium, the element was at last ensconced on the periodic table in 1905. All of its isotopes are radioactive.

Polonium has had a minor flare of celebrity in debate between creationists--who believe the universe, Earth, and the life upon it were created some 6,000 years ago during a seven-day period called Genesis Week--and those who subscribe to the Big Bang theory. At issue are "halos" of color found in granites. These halos are areas of damage in the crystalline structure of the rock.

Physicist Robert V. Gentry, a creationist, contends that these halos were formed through -particle emission. He says the size of these circles is linked to the amount of energy released during radioactive decay. He concludes that polonium provided the proper amount of energy to form these halos. Given polonium's half-live, measured in days, the radioactive decay of this element could form these circles of damage only if granites were created instantaneously, he argues.

Marie Curie
W. F. MEGGERS COLLECTION/AMERICAN INSTITUTE OF PHYSICS/SCIENCE PHOTO LIBRARY
This contrasts with the standard geological model for rock formation, which holds that the crystalline structure of granites developed though the slow cooling of magma deep within Earth over millions of years.

Not surprisingly, mainstream geologists refute Gentry's idea. They say these halos weren't caused by polonium. Instead, they say the circles of damage are probably due to the decay of other radioactive elements with a longer half-life--or that they aren't even created through radioactivity.

Neither the creationists or Big Bangers are budging. Polonium, meanwhile, is merrily forming and decaying.

With its short half-life, polonium isn't easy to come by. While the Curies processed pitchblende in a cast-iron basin to get polonium, the modern method, developed in 1934, involves bombarding bismuth-209 with neutrons to get polonium-210.

Oh, yes, polonium has its limited commercial uses. This metal is a source of -radiation and a heat source in space vehicles. It is also used in industrial equipment to eliminate static electricity.

Polonium is highly radioactive--it's hot. Its decay releases 140 W per g. This element should be handled with great care.

And that's no joke.


Cheryl Hogue is a senior editor who writes about environmental pollution for C&EN. She doesn't tell ethnic jokes but delights in limericks and puns.
Top


Chemical & Engineering News
Copyright © 2003 American Chemical Society