Greetings From the Island of Stability
By Oliver Sacks
Published: February 8, 2004
Last week the discovery of two new elements -- 113 and 115 -- was announced by a team of Russian and American scientists. There is something about such announcements that raises the spirits, thrills one, evokes thoughts of new lands being sighted, of new areas of nature revealed.
It was only at the end of the 18th century that the modern idea of an ''element'' was clearly defined, as a substance that could not be decomposed by any chemical means. In the first decades of the 19th century, Humphry Davy, the chemical equivalent of a big-game hunter, thrilled scientists and public alike by bagging potassium, sodium, calcium, strontium, barium and a few other elements. Discoveries rolled on throughout the next 100 years, often exciting the public imagination, and when, in the 1890's, five new elements were discovered in the atmosphere, these quickly found their way into H. G. Wells's novels -- argon was used by the Martians in ''The War of the Worlds''; and helium to make the antigravity material that transported Wells's heroes in ''The First Men in the Moon.''
The last naturally occurring element, rhenium, was discovered in 1925. But then, in 1937, there came something no less thrilling: the announcement that a new element had been created -- an element that seemingly did not exist in nature. The element was named ''technetium,'' to emphasize that it was a product of human technology.
It had been thought that there were just 92 elements, ending with uranium, whose massive atomic nucleus contained no less than 92 protons, along with a considerably larger number of neutral particles (neutrons). But why should this be the end of the line? Could one create elements beyond uranium, even if they did not exist in nature? When Glenn T. Seaborg and his colleagues at the Lawrence Berkeley National Laboratory in California were able to make a new element in 1940 with 94 protons in its huge nucleus, they could not at first imagine that anything more massive would ever be obtained, and so they called their new element ''ultimium'' (later it would be renamed plutonium).
If such elements with enormous atomic nuclei did not exist in nature, this was, presumably, because they were too unstable: with more and more protons in the nucleus repelling each other, the nucleus would tend toward spontaneous fission. Indeed, as Seaborg and his colleagues strove to make heavier and heavier elements (they created nine new ones over the next 20 years, and Element 106 is now named seaborgium in his honor), they found that these were increasingly unstable, some of them breaking up within microseconds of being made. There seemed good grounds for supposing that one might never get beyond Element 108 -- that this would be the absolute ''ultimium.''
Then, in the late 1960's, a radical new concept of the nucleus emerged -- the notion that its protons and neutrons were arranged in ''shells'' (like the ''shells'' of electrons that whirled around the nucleus). The stability of the nucleus of an atom, it was theorized, depended on whether these nuclear shells were filled, just as the chemical stability of atoms depended on the filling of their electron shells. It was calculated that the ideal (or ''magic'') number of protons required to fill such a nuclear shell would be 114, and the ideal number of neutrons would be 184. A nucleus with both these numbers, a ''doubly magic'' nucleus, might be, despite its enormous size, remarkably stable.
This idea was startling, paradoxical -- as strange and exciting as that of black holes or dark energy. It moved even sober scientists like Seaborg to allegorical language. He thus spoke of a sea of instability -- the increasingly and sometimes fantastically unstable elements from 101 to 111 -- that one would somehow have to leap over if one was ever to reach what he called the island of stability (an elongated island stretching from Elements 112 to 118, but having in its center the ''doubly magic'' isotope of 114). The term ''magic'' was continually used -- Seaborg and others spoke of a magic ridge, a magic mountain and a magic island of elements.
This vision came to haunt the imagination of physicists the world over. Whether or not it was scientifically important, it became psychologically imperative to reach, or at least to sight, this magic territory. There were undertones of other allegories as well -- the island of stability could be seen as a topsy-turvy, Alice-in-Wonderland realm where bizarre and gigantic atoms lived their strange lives. Or, more wistfully, the island of stability could be imagined as a sort of Ithaca, where the atomic wanderer, after decades of struggle in the sea of instability, might reach a final haven.
No effort or expense was spared in this enterprise. The vast atom-smashers, the particle colliders of Berkeley, Dubna and Darmstadt were all enlisted in the quest, and scores of brilliant workers devoted their lives to it. Finally, in 1998, after more than 30 years, the work paid off. Scientists reached the outlying shores of the magic island: they were able to create an isotope of 114, albeit nine neutrons short of the magic number. (When I met Glenn Seaborg in December 1997, he said that one of his longest-lasting and most cherished dreams was to see one of these magic elements -- but, sadly, when the creation of 114 was announced in 1999, Seaborg had been disabled by a stroke, and may never have known that his dream had been realized.)
Since elements in the vertical groups of the periodic table are analogous to one another, one can say with confidence that one of the new elements, 113, is a heavier analog of Element 81, thallium. Thallium, a heavy, soft, lead-like metal, is one of the most peculiar of elements, with chemical properties so wild and contradictory that early chemists did not know where to place it in the periodic table. Indeed, it was sometimes called the platypus of elements. Is thallium's new, heavier analog, ''super-thallium,'' as strange?
Similarly, the other new element, 115, is certain to be a heavier analog of Element 83, bismuth. As I write, I have a lump of bismuth in front of me, prismatic and terraced like a miniature Hopi village, and glittering with iridescent oxidation colors, and I cannot help wondering whether ''super-bismuth,'' if it could be obtained in massive form, would be as beautiful -- or perhaps more so.
And it could be possible to obtain more than a few atoms of these superheavy elements, for they may have half-lives of many years, unlike the elements preceding them, which vanish in split-seconds. For instance, atoms of Element 111, the heavier analog of gold, break down in less than a millisecond, and it is difficult to have more than an atom or two at a time, so we may never hope to see what ''super-gold'' looks like. But if we can make isotopes of 113, 114 (super-lead), and 115, which may have half-lives of years or centuries, we will have three enormously dense and strange new metals.
Of course, we can only guess at what properties 113 and 115 will possess. One can never tell in advance what the practical use or scientific implications of anything new might be. Who would have thought that germanium -- an obscure ''semi-metal'' discovered in the 1880's -- would turn out to be crucial to the development of transistors? Or that elements like neodymium and samarium, regarded for a century as mere curiosities, would turn out to be essential to the making of unprecedentedly powerful permanent magnets?
But such questions are, in a sense, beside the point. We search for the island of stability because, like Mount Everest, it is there. But, as with Everest, there is profound emotion, too, infusing the scientific search to test a hypothesis. The quest for the magic island shows us that science is far from being coldness and calculation, as many people imagine, but is shot through with passion, longing and romance.
Drawing (Drawing by Thomas Fuchs)