With help from newly developed equipment designed and built at
Michigan State
University, MSU researchers have been able to make first-of-its-kind
measurements
of several rare nuclei, one of which has been termed a "holy grail"
of experimental nuclear physics.
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| NSCL senior physicist Daniel Bazin adjusts the laboratorys National Science Foundation-funded radio frequency fragment separator, which allows boosts the ability to to search for proton-rich rare isotopes. Image: Greg Kohuth/MSU     |
The discoveries, made at MSU's
National Superconducting Cyclotron Laboratory using an isotope
purification
device, will help to refine theoretical models about how elements are
created
in the cosmos. Until now, this was beyond the technical reach of nearly all
of the world's nuclear science facilities.
To be published December 12 in Physical Review Letters, the paper
details how
the researchers were able to measure the nuclei of tin, cadmium and
indium.
"Tin-100, in particular, has been sort of a holy grail of experimental
nuclear physics," said NSCL senior physicist Daniel Bazin of one of the
isotopes, with 50 protons and 50 neutrons, described in the paper.
Within nuclear science, 50 is considered "magic" because it's one
of a handful of numbers associated with extra stability. The other magic
numbers
are 2, 8, 20, 28, 82 and 126.
It takes a magic number of protons or neutrons to fill the nested
energetic
shells that form the nucleus like stacking Russian matryoshka dolls. To
understand
the concept, consider that each carved doll similarly has a magic number of
marbles that precisely and completely fills the hollow interior. And
just as
a doll full of marbles neatly packed together is probably sturdier than one
that's only half or a quarter full, so too is a closed-shell nucleus
more stable
than its counterparts.
Tin-100 is one of the few "doubly magic" nuclei with magic numbers
of both protons and neutrons. Such nuclei are generally far more stable
than
other particles, especially at the fleeting, shape-shifting edge of nuclear
existence. Because of this stability, doubly magic nuclei serve as
useful semi-permanent
signposts to rare isotope researchers who troll the unexplored terrain
of the
nuclear landscape seeking to answer basic questions about the structure
of nuclear
matter and processes that create chemical elements inside stars.
The new experimental device, the radio frequency fragment separator,
provides
at least a hundredfold boost to NSCL's ability to filter out the few exotic
isotopes from the vast sea of other particles produced by its coupled
superconducting
cyclotrons and downstream magnets. Funding for the equipment was
provided by
the National Science Foundation.
This newfound filtering ability resulted in the first production and
measurement
in North America of tin-100, which has been eagerly pursued by
experimentalists
since at least the mid-1990s. GSI in Germany and GANIL in France are the
only
other nuclear science facilities in the world to have successfully produced
and studied the rare, proton-rich isotope of tin, an element extensively
used
for thousands of years in everything from ancient spears and knives to cars
and modern electronics.
In their paper, a draft version of which is available online on the
arxiv.org
preprint server (http://arxiv.org/abs/0810.3597), Bazin and his
collaborators
also report the measurement of half-lives of the cadmium-96 (48 protons and
48 neutrons) and indium-98 (49 protons and 49 neutrons) isotopes.
The announcement of the observation of the three rare isotopes builds
on recent
NSCL success in creating nuclear matter that otherwise only exists in
extreme
environments in space, such as exploding stars. In fall 2007, the
laboratory
reported the discovery of three neutron-rich isotopes of magnesium and
aluminum
in the journal Nature, a finding that received considerable media attention
in the science and mainstream press.
The laboratory is currently undertaking a major MSU-funded upgrade, the
centerpiece
of which is a new low-energy reaccelerator that will be used to conduct
astrophysical
research. When this upgrade is completed in summer 2010, NSCL will be
only facility
in the world capable of offering experimentalists the chance to conduct
research
with fast, stopped and reaccelerated beams of rare isotopes.
A world leader in rare isotope research and nuclear science education,
NSCL
is a user facility serving 700 researchers in 32 countries.
Posted December 10th, 2008
