Experiments reveal a neutron halo around neutron-rich magnesium nuclei

August 29, 2014
Figure 1: Neutron-rich magnesium nuclei have a neutron halo that extends beyond the tightly packed core of the nucleus. Credit: Ken-ichiro Yoneda, RIKEN Nishina Center for Accelerator-Based Science

Most stable atomic nuclei are made up of roughly an equal number of protons and neutrons. With the right equipment, however, physicists can create nuclei with many additional neutrons. These neutron-rich nuclei are short-lived but represent an important tool for developing a better understanding of how the elements in the Universe were created.

A collaborative study led by Nobuyuki Kobayashi and Takashi Nakamura from the Tokyo Institute of Technology involving researchers from the RIKEN Nishina Center for Accelerator-Based Science has now revealed that the extra neutrons in a neutron-rich nucleus produce a neutron halo.

The researchers used RIKEN's Radioactive Isotope Beam Factory to produce of magnesium-37, consisting of 25 neutrons and 12 protons. To examine its properties, the researchers observed what happened when these nuclei were bombarded against a lead target. "We found that the magnesium-37 nuclei broke up easily into a magnesium-36 core and a single neutron," says Kobayashi. "Thus, we concluded that magnesium-37 has a neutron halo."

Neutron halos are a dilute cloud of neutrons that surround the more tightly packed neutrons and protons found at the center of a nucleus. They have been identified in the past, but predominantly in nuclei with fewer than 20 neutrons. Magnesium-37 is so far the heaviest nuclei to have been found to have a nuclear halo. Evidence of a halo-like structure also implies that magnesium-37 nuclei are deformed and do not conform to the conventional spherical shape.

The researchers then performed a similar experiment using a carbon target. Whereas the lead-target experiments revealed the reaction of the nuclei to electrostatic forces, the use of a carbon target made it possible to study the response of magnesium-37 to nuclear forces, which are sensitive to the rotational motion of the neutrons. The halo found in previously studied light nuclei, in which the core is surrounded by a single neutron, have no rotation and are known as s-wave halos. In contrast, Kobayashi and his colleagues found that the halo neutron in magnesium-37 had a measurable angular momentum or rotation, called a p-wave halo.

The results provide a vital insight into why some nuclei are stable while others decay. "Our results indicate that the formation of halos may be a universal feature in neutron-rich nuclei," explains Ken-ichiro Yoneda, one of the RIKEN researchers who contributed to the project. "The reason why they exist, however, is still unclear. We hope to accumulate more detailed information about other neutron-rich nuclei so that we can better understand the halo-formation mechanism."

Explore further: Observation of unexpectedly deformed neutron-rich magnesium nuclei prompts rethink of nuclear shell structure

More information: Kobayashi, N., Nakamura, T., Kondo, Y., Tostevin, J. A., Utsuno, Y., Aoi, N., Baba, H., Barthelemy, R., Famiano, M. A., Fukuda, N. et al. "Observation of a p-wave one-neutron halo configuration in 37Mg." Physical Review Letters 112, 242501 (2014). DOI: 10.1103/PhysRevLett.112.242501

Related Stories

Evidence for a new nuclear 'magic number'

October 9, 2013

Researchers have come one step closer to understanding unstable atomic nuclei. A team of researchers from RIKEN, the University of Tokyo and other institutions in Japan and Italy has provided evidence for a new nuclear magic ...

Recommended for you

Quantum internet goes hybrid

November 22, 2017

In a recent study published in Nature, ICFO researchers led by ICREA Prof. Hugues de Riedmatten report an elementary "hybrid" quantum network link and demonstrate photonic quantum communication between two distinct quantum ...

Enhancing the quantum sensing capabilities of diamond

November 22, 2017

Researchers have discovered that dense ensembles of quantum spins can be created in diamond with high resolution using an electron microscopes, paving the way for enhanced sensors and resources for quantum technologies.

Study shows how to get sprayed metal coatings to stick

November 21, 2017

When bonding two pieces of metal, either the metals must melt a bit where they meet or some molten metal must be introduced between the pieces. A solid bond then forms when the metal solidifies again. But researchers at MIT ...

Imaging technique unlocks the secrets of 17th century artists

November 21, 2017

The secrets of 17th century artists can now be revealed, thanks to 21st century signal processing. Using modern high-speed scanners and the advanced signal processing techniques, researchers at the Georgia Institute of Technology ...

0 comments

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.