In addition to lithium-11 and berrylium-14, the neutron-rich isotope carbon-22 (22C) could also be a Borromean ‘halo’ nucleus, a team of researchers from Japan has reported in Physical Review Letters. The finding will allow physicists to test fundamental nuclear models in nuclei containing a high ratio of neutrons to protons.
To a good approximation, the atomic nucleus is a uniformly dense distribution of protons and neutrons packed into a spherical drop a few femtometers (10-15 m) in radius. However, isotopes that contain more than 2 to 3 neutrons for every proton start to ‘leak’ neutrons. For a very few of these neutron rich nuclei, one or two excess neutrons form a loosely bound orbit—or halo—about the nuclear core.
The two-neutron halo nucleus is a special quantum three-body system: if one of the neutrons in the halo is removed, the remaining part falls apart. This interdependent system of two neutrons and a core is called a ‘Borromean’ nucleus, because of its similarity to the three, interlocked Borromean rings.
“[Previously], only the instability of 21C suggested that 22C might be a Borromean nucleus, and hence have a two-neutron halo,” explains Kanenobu Tanaka from the RIKEN Nishina Center for Accelerator-Based Science in Wako. “To study [whether 22C has the halo structure], we assembled a large-scale collaboration among institutions with expertise on many techniques. For example, special detector settings had to be prepared and creating the beams of carbon isotopes required careful tuning.”
Nuclei with a high neutron-to-proton ratio are unstable and can only be made artificially. Using the RIKEN projectile fragment separator (RIPS) the researchers produced three isotopes of carbon—19C, 20C and 22C—from the fragments of a high-energy beam of argon that impinged on a tantalum target. They then bombarded the carbon nuclei against a liquid hydrogen cell. Since larger nuclei are more likely to strike the hydrogen protons in the liquid, the researchers could determine the size of each carbon isotope by measuring its frequency of collision.
Tanaka and colleagues found that the radius of the 22C was about 5.4 fm, which is more than 50% larger than theoretical predictions, providing strong evidence that 22C is a halo nucleus and making it the heaviest Borromean nucleus ever observed.
“This finding opens the possibility to find halo nuclei in a more extended region of the nuclear chart and will give us greater insight into the mechanism of halo formation,” says Tanaka.
The corresponding author for this highlight is based at the Research Instruments Group BigRIPS Team, RIKEN Nishina Center for Accelerator-Based Science
1. Tanaka, K., Yamaguchi, T., Suzuki, T., Ohtsubo, T., Fukuda, M., Nishimura, D., Takechi, M., Ogata, K., Ozawa, A. Izumikawa, T. et al. Observation of a large reaction cross section in the drip-line nucleus 22C. Physical Review Letters 104, 062701 (2010)
gro-pr | Research asia research news
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