Newly Created Forms of Magnesium and Aluminum
New isotopes push the edge of nuclear existence
How many neutrons can an atomic nucleus hold? Possibly a lot more than current scientific models predict. That's the conclusion a team of physicists--funded by the National Science Foundation (NSF)--reached after creating three ultra-heavy isotopes of magnesium and aluminum.
The research results appear in the Oct. 25 journal of Nature. Lead author Thomas Baumann and his colleagues created the isotopes at Michigan State University's National Superconducting Cyclotron Laboratory (NSCL).
In an experiment that ran earlier this year at NSCL, the researchers created and detected one new ultra-heavy isotope of magnesium, magnesium-40 with 12 protons and 28 neutrons, and two new ultra-heavy types of aluminum, aluminum-42 with 13 protons and 30 neutrons, and aluminum-43 with 13 protons and 30 neutrons.
According to one of the leading theoretical models, aluminum-42 shouldn't exist. That it does suggests the outer limit for neutron stuffing, called "the dripline" by nuclear physicists, suggests the possibility of more novel, neutron-rich isotopes than previously thought. Right now, the dripline limit is only known for the eight lightest elements, hydrogen to oxygen. The heaviest isotope that can exist for an element remains unanswered for all but eight of the 100 or so elements on the Periodic Table.
"The coupled cyclotron facility at MSU is a worldwide flagship facility funded by NSF to explore the frontiers of nuclear science and the extreme limits of the strong force in holding a nucleus together," said NSF Nuclear Physics Program Director Ani Aprahamian. "The NSCL funded by the NSF brings together a talented scientific staff coupled with the most advanced accelerator and detection capabilities to advance nuclear science far beyond what we know today."
For a long time, several facilities like NSCL around the world have searched for these isotopes, particularly magnesium-40, without luck. Creating and measuring rare isotopes is always needle-in-a-haystack work that requires researchers to hunt for a few desired nuclei from a swarm of fast moving and mostly uninteresting particles. But in this experiment, NSCL researchers achieved a 100- to 1,000-fold boost in their ability to filter out what can be thought of as white noise. They did so by using a dual-filtering process that detected and measured isotopes so rare they represent only one in every billion million particles that passed by the detectors. This experiment marks one of the first uses of two-stage separation in the world and the first time the technique has been tried at NSCL.
The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2017, its budget is $7.5 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards.
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