EAST LANSING, Mich., Oct. 30, 2007 -- The creation of three magnesium and aluminum isotopes stake new territory on the nuclear landscape and suggest that variants of everyday elements might exist that are heavier than current scientific models predict.
Thomas Baumann and his colleagues created the isotopes at the Michigan State University (MSU) National Superconducting Cyclotron Laboratory (NSCL).
"It's been a long-standing project since the beginning of nuclear science to establish what isotopes can exist in nature," said Dave Morrissey, a chemistry and professor at MSU and an author of a paper about the findings (Nature, Oct. 25). "This result suggests that the limit of stability of matter may be further out than previously expected; really, it shows how much mystery remains about atomic nuclei."
Images from the NSCL logbook in which researchers first recorded the successful discovery of magnesium-40. The colored highlights and scrawled comment "Let the celebrations begin!" reflect their excitement. (Photo: NSCL)
Particles that comprise atomic nuclei, protons and neutrons, are held together by the nuclear force -- one of the four fundamental forces that collectively describe the interactions of all matter in the cosmos, and the subject of much scientific inquiry since the 1930s.
One goal is defining the neutron-limit, the maximum number of neutrons that can be loaded onto a given nucleus. This limit, referred to as the neutron-dripline, is known only for the eight lightest elements, ranging from hydrogen to oxygen. So one very basic question -- what’s the heaviest isotope of a given element that can exist? -- remains unanswered for all but eight of the 100 or so elements in the periodic table.
In an experiment that ran earlier this year at NSCL, researchers created and detected three new ultraheavy isotopes of magnesium and aluminum: magnesium-40, with 12 protons and 28 neutrons; aluminum-42, 13 protons and 29 neutrons; and aluminum-43, 13 protons and 30 neutrons. If the everyday version of aluminum was a 160-pound adult, aluminum-43 would weith 255-pounds.
Researchers have created never-before-seen isotopes of magnesium and aluminum -- represented here by the two colored squares floating in blackness. The extra weight refers to the additional neutrons stuffed into the nucleus by a dual filtering process carried out at Michigan State University's National Superconducting Cyclotron Laboratory. (Image: Alex Paisons, Michigan State University)
"For a long time, several facilities like NSCL around the world have searched for these isotopes, particularly magnesium-40, without luck," said Thomas Baumann, NSCL beam physicist and lead author of the study. "That we were able to succeed is just one reason why, when I talk to students who are thinking about doing graduate work in nuclear physics, I always tell them this is the best place they can be. It's one of the top three facilities in the world where you can do this kind of research."
The next step down this path of accelerator-based physics, Baumann added, is to push further toward the edge of nuclear existence in an effort to reach the neutron dripline for these and other elements -- something that will require a major technical upgrade of the laboratory. NSCL has published plans on its Web site for a next-generation isotope science facility.
"To stay world-competitive, NSCL needs to replace its aging cyclotrons with a modern driver accelerator, a superconducting linear accelerator," said Konrad Gelbke, NSCL director and a professor of physics and astronomy. "The concept is fully developed, and we hope that the federal government will make the needed investment so that we can build on our strength and remain the national leader in rare isotope research and education. All we need is money; the ideas and the know-how are in place."
The research was supported by the National Science Foundation and MSU. For more information, visit: www.nscl.msu.edu
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