Experiments performed with the exotic nucleus tin-101, which has a single neutron orbiting tin-100's closed shell of 50 protons and 50 neutrons, indicate an unexpected reversal in the ordering of lowest states in the nucleus. The finding appears to violate a standard scenario offered by the nuclear shell model that has been the cornerstone for understanding the atomic nucleus for more than half a century.
The international team of experimentalists and theorists was led by Iain G. Darby of the University of Tennessee (UT), who is now in Belgium, and Robert Grzywacz, a physics professor at UT and a former Wigner Fellow at ORNL. The experiment, performed at ORNL's Holifield Radioactive Ion Beam Facility, found that the ground states of orbiting neutrons unexpectedly swap when three neutrons are added to the closed-shell tin-100 nucleus.
"In fact, previously the ground state of tin-101 was assumed to be identical to that of tin-103, tin-105, and tin-107. Those conform to the standard picture. But we've found that tin-101 has a flipped ground state," Grzywacz said.
The researchers theorize that the swapping of ground-state spins between tin-101 and tin-103 is due to the neutrons' unusually strong orbital dependence of the pairing interaction and the relatively small difference between orbital energy states in tin-101.
"Neutrons tend to dance in pairs, much like Cooper pairs of electrons in superconductors. But because their angular momentum adds to zero, the pairing shouldn't affect the spin of the nucleus if only few neutrons are involved" said ORNL and UT researcher Witold Nazarewicz.
Grzywacz and Nazarewicz explained that, in the standard shell model, the neutron pairing energy weakly depends on the particle's state. "But it so happens that pairing interaction is different in those two orbits, one with higher energy and one lower. It is orbital dependent," said Nazarewicz, who is scientific director at the Holifield Facility. "With tin-101, those properties are governed by one neutron. If you add two more neutrons, the ground state is determined by the neutron superconductivity, which is very unusual. "
"In practice, the final picture is the two neutrons pair strongly and kick out the third--odd--neutron in tin-103 into another orbit," said Grzywacz. "Three's a crowd."
The experiment required the unique radioactive ion beam capabilities of the Holifield Facility at ORNL, plus digital signal processing instrumentation developed at ORNL to measure the extremely fast alpha particle decays in the neutron-deficient and very unstable tin isotopes. Tin-101 was made in the decay of the extremely short-lived, lightest-known alpha emitter tellurium-105, which was previously discovered by the ORNL-UT team.
The theoretical calculations, based on parameter-free, state-of-the-art nuclear models, were performed in Oslo, Norway, and in Oak Ridge, Tenn.
"We were developing these experimental methods for almost a decade and, combined with advances in computational methods and access to supercomputers such as Jaguar and Kraken at ORNL, they are now bearing fruit," said Grzywacz.
The results of the research, which was funded in part by DOE's Office of Nuclear Physics, have been accepted for publication in Physical Review Letters.
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
Bill Cabage | EurekAlert!
SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University
Molecule flash mob
19.01.2017 | Technische Universität Wien
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences