Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New 'Doubly Magic' Research Reveals Role of Nuclear Shell

07.06.2010
Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL), the University of Tennessee (UT) and six collaborating universities have performed an unprecedented nuclear reaction experiment that explores the unique properties of the “doubly magic” radioactive isotope of 132Sn, or tin-132.

The research, published today in the journal Nature, is part of a broad scientific effort to understand nucleosynthesis, or the process by which the higher elements (those in the periodic table above iron) are created in the supernova explosions of stars.

This research focused on the so-called r-process, responsible for the creation of about half of those heavy elements. This process involves interactions at very high energies of highly unstable and rare isotopes that do not naturally occur on earth, but that can be created in the laboratory.

The research was performed at ORNL’s Holifield Radioactive Ion Beam Facility, a nuclear physics national user facility supported by the DOE Office of Science.

“Magic” nuclei define important way stations of relative stability as heavier elements are built up out of protons and neutrons (collectively known as nucleons).

Researchers relied on the “nuclear shell model” theory, which envisions the atomic nucleus as a series of shells, each representing a certain energy level and each containing a certain number of nucleons (protons or neutrons). As nucleons are added to the nucleus, they “fill” the successive shells: the first shell is filled with 2, the second with 8, and then on up to 20, 28, 50, 82, and 126, in succession. These numbers are “magic” because the nucleons in these shells are thought to be more strongly bonded--and hence relatively more stably configured--than the next nucleon that is added.

Tin-132 is a radioactive isotope of the familiar element tin with special properties--it is one of a small group of isotopes with a “magic” number of both protons and neutrons, making this nucleus “doubly magic.” It has 50 protons and 82 neutrons.

In this experiment, a neutron was transferred to a tin-132 nucleus to create tin-133, and the effects of adding this additional neutron were carefully measured.

"The experiment's measurement is critical to benchmarking the nuclear shell model, to extrapolating theoretical nuclear models beyond the reach of current experimental facilities and to simulating the synthesis of nuclei heavier than iron in the cosmos," UT Department of Physics and Astronomy researcher and lead author Kate Jones said.

In the Nature paper, the team shows that tin-132 represents a good example of the shell model paradigm and that the properties of the states of tin-133 are to a large extent determined by the last, unpaired neutron.

"As such, tin-132 can now be used as a textbook example of a doubly-magic nucleus and the principal benchmark for extrapolations to nuclei currently out of experimental reach that are crucial for production of heavy elements in stellar explosions," Jones said, adding, “Short-lived isotopes are important to astrophysical processes, and we want to understand how the heavy elements, such as those beyond iron, were produced.”

The Holifield facility enables nuclear scientists to produce beams of radioactive nuclei, then separate a particular isotope for experimentation with the world’s most powerful electrostatic accelerator.

Nuclei can be classified in three ways: stable nuclei that never decay, known radioactive nuclei, and unknown, extremely short-lived nuclei. Doubly magic nuclei have properties that make them good launching pads to explore the structure of unknown nuclei with large neutron or proton numbers that do not naturally occur on Earth.

“A century ago, all nuclear physicists could study were the stable isotopes that make up all the atoms of elements of things around us,” said Jones.

However, nuclear processes — such as those that took place to create the matter around us — produce both stable elements and radioactive isotopes with nuclei that are either proton or neutron-rich.

Witold Nazarewicz, the Holifield Facility's scientific director, explained how the experiments were performed at the ORNL facility.

“We produce some of the radioactive nuclei--the very short-lived nuclei like tin-132. We then use them as beams to further push the boundaries,” Nazarewicz said, “to get closer and closer to the territory of unknown nuclei.”

Despite being comparatively strongly bound, tin-132 itself only lasts about 40 seconds. To produce the fleeting nuclei of tin-132, scientists shot protons at a uranium target, producing a primary beam of several kinds of radioactive nuclei from which tin-132 is carefully selected.

Jones and Nazarewicz said such pioneering research is rapidly changing basic theoretical models of nuclear structure because scientists’ understanding of the inner workings of the nucleus is altered the further into unstable, neutron-rich territory they are able to observe.

“It was only a decade ago we managed to produce beams of neutron-rich isotopes by proton-induced fission of uranium” said Nazarewicz. “Now we see the nuclear structure shifting the more neutron-rich we get, and our understanding of the nuclear shells, which is basically textbook knowledge since the 1940s, will likely change.”

The research was supported by the DOE Office of Science, the National Science Foundation, and the UK Science and Technology Funding Council.

ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science.

NOTE TO EDITORS: You may read other press releases from Oak Ridge National Laboratory or learn more about the lab at http://www.ornl.gov/news. Additional information about ORNL is available at the sites below:

Twitter - http://twitter.com/oakridgelabnews
RSS Feeds - http://www.ornl.gov/ornlhome/rss_feeds.shtml
Flickr - http://www.flickr.com/photos/oakridgelab
YouTube - http://www.youtube.com/user/OakRidgeNationalLab
LinkedIn - http://www.linkedin.com/companies/oak-ridge-national-laboratory
Facebook - http://www.facebook.com/Oak.Ridge.National.Laboratory
MEDIA CONTACT: Katie Freeman
ORNL Communications & External Relations
(865) 574-4160, freemanke@ornl.gov

Katie Freeman | Newswise Science News
Further information:
http://www.ornl.gov

More articles from Physics and Astronomy:

nachricht NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>