Nuclear physicists examine oxygen's limits

Sep 14, 2007
Moving MoNA During 2007 NSCL Reconfiguration
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. Credit: NSCL

Physicists at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University have made a unique measurement of an exotic oxygen nucleus, leading scientists one step closer to deciphering the behavior of the element at its limits of existence.

The finding, published in Physical Review Letters, confirms a relatively new theoretical model that predicts dramatic changes in structure as one looks at heavier and heavier oxygen nuclei.

In the experiment, researchers measured a never-before-seen energy state of oxygen 23—one of the heaviest oxygen isotopes that exist.

"It was very exciting to see an experiment that was able to observe this [energy] state very close to where we predicted," said Alex Brown, a professor a NSCL who was involved in the shaping of the theory.

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.

Source: Michigan State University

Explore further: Decoding the brain: Scientists redefine and measure single-neuron signal-to-noise ratio

Related Stories

Explainer: What are fundamental particles?

Mar 20, 2015

It is often claimed that the Ancient Greeks were the first to identify objects that have no size, yet are able to build up the world around us through their interactions. And as we are able to observe th ...

Humble neutron is valuable tool in geology

Mar 16, 2015

With the ability to analyse the properties of the Earth's internal components to the atomic scale in conditions only found kilometres below our feet, recent studies have allowed geoscientists to study our ...

Exploring the universe with nuclear power

Feb 02, 2015

In the past four decades, NASA and other space agencies from around the world have accomplished some amazing feats. Together, they have sent manned missions to the Moon, explored Mars, mapped Venus and Mercury, ...

Revealing secrets of atomic nuclei

Jan 21, 2015

Individual protons and neutrons in atomic nuclei turn out not to behave according to the predictions made by existing theoretical models. This surprising conclusion, reached by an international team of physicists ...

Recommended for you

The ins and outs of quantum chromodynamics

11 hours ago

Quarks and antiquarks are the teeny, tiny building blocks with which all matter is built, binding together to form protons and neutrons in a process explained by quantum chromodynamics (QCD).

Engineers give invisibility cloaks a slimmer design

13 hours ago

Researchers have developed a new design for a cloaking device that overcomes some of the limitations of existing "invisibility cloaks." In a new study, electrical engineers at the University of California, ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.