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Undergraduates from 10 different institutions
assembled the Modular Neutron Array (MoNA) at the Michigan State
University National Superconducting Cyclotron Laboratory in 2002.
MoNA collaborators were back to help move the detector as part of
the 2007 NSCL reconfiguration, a $2.7 million project that will
keep the laboratory's science program at the cutting edge of
nuclear science and allow for tests of technologies critical to
next-generation rare isotope beam facilities. Pictured here from
left to right helping to move MoNA: Amy Deline, Central Michigan
University; Artemis Spyrou, NSCL; Greg Christian, NSCL; Ruth Howes,
Marquette University.
NSCL beam physicist Thomas Baumann adjusts the
Modular Neutron Array (MoNA). The device at the Michigan State
University National Superconducting Cyclotron Laboratory detects
neutrons that fly off of reactions with very high efficiency,
allowing for experiments that take a fraction of the time to
examine the most exotic of rare isotopes.
Fotos � NSCL
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Atomic nuclei are composed of protons and
neutrons, only certain combinations of which can exist. Each element
- determined by the number of protons in its nucleus
- comes in a variety of flavors with different numbers of
neutrons, creating isotopes. The search for the maximum number of
neutrons that can fit into a given element's nucleus lies at the
forefront of nuclear physics research.
Moving towards the limit of nuclear stability often leads to strange
behavior, such as unexpected changes in nuclear structure.
"We thought we understood the nuclear forces well," said Andreas
Schiller, an assistant professor at Ohio University and lead
researcher on the study. "But it turns out, when we go to extreme
ratios of neutrons and protons, the forces in those areas still hold
surprises."
While oxygen 23 contains 8 protons and 15 neutrons, stable form of
oxygen, making up the bulk of the oxygen found on Earth, has only 8
neutrons.
A few years ago, scientists tweaked an older version of the theory of
atomic nuclei to try to explain some startling phenomena among the
heavier oxygen isotopes. The new calculations predicted more dramatic
changes in structure among the heavier oxygen isotopes. The experiment,
which was conducted at NSCL, confirms these predictions.
Looking at the excited states of a nucleus -
reached by adding extra energy into it - is a
good way to understand the forces inside it, said Michael Thoennessen,
associate director of nuclear science at NSCL and co-author of the
paper.
The result paves the road to studying the neighboring oxygen 24
- the heaviest possible oxygen isotope.
Many more mysteries remain to be explored, physicists say. As many as
8,000 nuclei are predicted to exist, but so far only 2,000 have been
observed.
The experiment, funded by the National Science Foundation, was the
first to yield new information from two tailored NSCL tools, which
came on line only recently. One device, the Modular Neutron Array,
detects neutrons with high efficiency, and the other, the sweeper
magnet, uses NSCL's superconducting magnet technology to allow a
higher percentage of sought-after particles to pass.
These devices make it possible to explore isotopes farther towards the
extreme edges of existence, by making experimental run times up to
seven times shorter.
"Without them you couldn't do the experiments," Thoennessen said.
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