Level 5 Reading 10B

Reading 10B

ELEMENT HUNTERS All the elements found in nature—the different kinds of atoms—were found long ago. To find a new one these days, you need to create it. Everything you know and love on Earth, and everything you don't, is built of elements—the different types of atoms. Most of them are billions of years old, scattered into space by the Big Bang or by exploding stars. They were then incorporated into the newly born Earth, endlessly recycled as they moved from rock to bacteria, president, or mouse. In the late 1800s, the Russian chemist and inventor Dmitry Mendeleyev tried to make sense of Earth's elements, grouping them by mass—the scientific term for weight— and other attributes in his periodic table of the elements. Later, scientists connected the order of elements in the periodic table to the structure of atoms. Each element got a number: its atomic number— the number of protons in its atomic nucleus. By 1940, researchers had discovered every element on Earth, right up to uranium (element 92). They had filled in every gap Mendeleyev had left in his table, but they weren't finished. Beyond uranium lay a world of possibilities—elements too radioactive and unstable to have survived billions of years. To explore that world, you have to create it first. The first steps of creation not only extended the periodic table, but played a fateful role in world history. It was 1940, the year after World War ll began, and U.S. scientists led the race to create new elements. Element 93, neptunium, was created in a laboratory at the University of California, Berkeley. The next year, Glenn Seaborg and his colleagues at the same university produced element 94, plutonium. Seaborg was promptly recruited to the Manhattan Project to create an atomic bomb for the U.S. military. The intensified level of nuclear research in the United States did not go unnoticed by the world's other superpower at the time—the Soviet Union. Georgy Flerov was a prominent physicist who had helped launch that country's nuclear weapons research. Early in World War II, Flerov had noticed that the flow of articles about radioactive elements from U.S. and German scientists had suddenly stopped. This heightened secrecy led him to suspect that they were building atomic bombs, TWENTY-SIX NEW ELEMENTS Since the 1940s, scientists have probed the frontiers of the atomic nucleus, synthesizing heavier elements one by one. The first step beyond uranium (the heaviest natural element) was neptunium, number 93 in the periodic table. The synthetic atoms are all radioactive: They decay into lighter elements, sometimes within milliseconds. In general, the heavier the element, the shorter its half-life. For decades researchers have been searching for the "island of stability," where "magic numbers" of protons and neutrons might combine to make superheavy atoms that last long enough to be studied.

and in April 1942, he wrote to Soviet leader Joseph Stalin explaining his fears. Flerovs suspicions were confirmed, and Stalin asked Russian physicists to build a bomb, too. For his part in the war effort, Flerov was rewarded with a car, a house, and, most significantly, a laboratory in the town of Dubna, north of Moscow. There, Flerov focused his attention on the hunt for new elements. His American counterpart, Glenn Seaborg, returned to Berkeley after helping to engineer the bomb that the U.S. military dropped on Nagasaki at the end of the war. He continued to make new elements, with less fateful applications— smoke detectors, for instance—or no applications at all. By 1955, his team had gotten as far as element 101—he named it mendelevium. For a time it seemed Mendeleyev's table might end there, with his namesake. The protons in an atomic nucleus are always trying to tear it apart; their positive electric charges repel one another. Neutrons—electrically neutral particles that out number the protons—help bind the nucleus together. But that binding force works only at extremely close range, and it weakens sharply as the size of the nucleus increases. So there has to be a final box on the periodic table, a maximum size beyond which an atom won't be stable even for an instant. With mendelevium, which has a half-life of 51.5 days, researchers seemed to be getting close to the final box. Beyond Mendelevium The Berkeley team continued its research regardless, rivaled by Flerovs team in Dubna. From 1965 to 1974, Berkeley claimed to have produced elements 102-106—but so did the Dubna lab. Although those short-lived elements died within hours, the tense disputes over who made them first were fueled by the competitive atmosphere of the Cold War. In the end, a spirit of compromise prevailed: Element 105 was named dubnium and element 106 seaborgium. Meanwhile, theorists had given a new purpose to the quest for elements. They calculated that a very large nucleus might be surprisingly stable if it had "magic numbers" of protons and neutrons. That insight, if correct, would change everything. It would mean that there could be an "island of stability" where extremely heavy elements might last minutes, weeks, or even thousands of years. Around the time that this new theory appeared, a brilliant physicist named Yuri Oganessian joined Flerov's lab in Dubna. The island of stability had captured his imagination. However, reaching it seemed to him an impossible task at that point. The Berkeley and Dubna labs had gotten only as far as element 106 by shooting light atoms against heavy ones with such force that they joined to create a single superheavy nucleus. But beyond 106, the collisions were so energetic that they were ripping the new nucleus apart before it even formed. To overcome this problem, Oganessian proposed that shooting slightly heavier atoms at lighter targets might create gentler collisions that were more likely to create new elements. Unfortunately, before he could put his proposal into action, a lab in Darmstadt, Germany, used the idea to make elements 107 through 112. Oganessian's historic moment would have to wait another quarter century. In the coming years, the Dubna lab went through hard times. Flerov died in 1990; the Soviet Union collapsed in 1991. The lab went months without being able to pay its researchers. Scientists gathered mushrooms in the forests and fished in the Volga River. Oganessian, now in charge of the lab, could have directed it toward more practical goals and made some money for himself and his staff, but he decided instead to continue toward element 114 and the promised island of stability. Achieving the Dream To make element 114, Oganessian would shoot calcium at plutonium. He persuaded U.S. physicists at the Lawrence Livermore National Laboratory in California— who just a few years earlier had been his rivals—to give him a small amount of plutonium. The plan was to use a cyclotron to shoot a beam of calcium atoms at high speed into a thin sheet of metal covered with the precious plutonium atoms. Among the trillions of atoms spraying out the other side— the metal sheet was thinner than hair—Oganessian expected at most one atom of element 114. His team—along with Livermore's—invented a new device to detect it. They turned the cyclotron on in November 1998. It wasn't a very trust worthy piece of machinery, and it required constant attention. Nevertheless, in late November, the cyclotron managed to produce a single atom of element 114. It lasted only a few seconds— but that was thousands of times longer than would be expected if there were no island of stability. It also proved that the calcium method worked. Dubna and other labs have since made elements 115-118, and isotopes with different numbers of neutrons. They are still nowhere near the island's peak, where an element might last years, but the creation of element 114 was the great breakthrough that Oganessian had been dreaming about for decades. It wasn't until 2011, however, that element 114 was officially admitted to the periodic table. This is because no newly discovered element is officially recognized until another laboratory can duplicate the experiment, which sometimes takes years. Element 114 was given the name flerovium. This belated but welcome recognition came when Oganessian was 78 years old. After such a triumph, other scientists might have decided it was time to retire to a quiet and grateful life— but not Yuri Oganessian. The island of stability still captures his imagination, inspiring him on to further discoveries. As Oganessian put it, "We have discovered the island. Now it is time to explore it, to walk along its western beach." Techniques must be developed to shoot the magic number of neutrons into flerovium to reach its peak of stability. Scientists need to discover if there are peaks at other elements. Although at the moment those goals seem almost impossible, Oganessian has no intention of giving up the hunt for new elements.

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