Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Atomic Nucleus with Halo: For the First Time, Scientists Measure the Size of a One-Neutron Halo with Lasers

Atomic nucleus of beryllium is three times as large as normal due to halo / Publication in Physical Review Letters

Atomic nuclei are normally compact structures defined by a sharp border. About twenty-five years ago, it was discovered at the University of California in Berkeley that there are exceptions to this picture: Certain exotic atomic nuclei contain particles that shear off from the central core and create a cloud, which surrounds the central core like a 'heiligenschein' or halo.

The \'halo\' nucleus 11Be consists of a core of 10Be and loosely bound neutron. The neutron orbits at a mean distance of 7 fm from the center-of-mass. illustration: Dirk Tiedemann, Institute of Nuclear Chemistry

An example of such a halo occurs in beryllium-11, a specific isotope of the metal beryllium. Here, the halo is made up of a single neutron. For the first time ever, scientists at the Institute of Nuclear Chemistry of the Johannes Gutenberg University Mainz in cooperation with colleagues from other institutes have succeeded in precisely measuring this one-neutron halo by means of a laser, and in evaluating the dimensions of the cloud. By studying neutron halos, scientists hope to gain further understanding of the forces within the atomic nucleus that bind atoms together, taking into account the fact that the degree of displacement of halo neutrons from the atomic nuclear core is incompatible with the concepts of classical nuclear physics.

"We intuitively imagine the atomic nucleus as a compact sphere consisting of positively charged protons and uncharged neutrons," explains Dr Wilfried Nörtershäuser of the Institute of Nuclear Chemistry. "In fact, we have known since the 1980s that atomic nuclei of certain neutron-rich isotopes of the lightest elements - lithium, helium and beryllium - completely contradict this conception." These isotopes consist of a compact nuclear core and a cloud made of diluted nuclear material - called 'heiligenschein' or 'halo'. A halo consists mostly of neutrons that are very weakly bound to the nuclear core, "normally with only one-tenth of the usual binding energy of a neutron inside the core," explains Nörtershäuser.

The discovery of these exotic atomic nuclei created a new area of research, which Nörtershäuser as the head of a young investigators group funded by the German Helmholtz Association has pursued since 2005 at the University in Mainz and at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt. Measuring halo nuclei is extremely difficult, since they can only be artificially created in minute amounts. In addition, these synthesized nuclei decay within seconds, mostly even in milliseconds.

Nörtershäuser's team has now succeeded for the first time in measuring the nuclear charge radius in beryllium-11. This nucleus consists of a dense core with 4 protons and 6 neutrons and a single weakly bound neutron that forms the halo. In order to accomplish this ultra-precise laser spectroscopic measurement, the scientists used a method developed 30 years ago at the University of Mainz, but combined it now for the first time with the most modern techniques for precise laser frequency measurement, i.e., by employing an optical frequency comb. This combination alone was not sufficient, though. Only by further expanding the method using an additional laser system it was possible to achieve the right level of precision. The technique was then applied to beryllium isotopes at the Isotope Separator On Line (ISOLDE) facility for radioactive ion beams at the European Organization for Nuclear Research (CERN) in Geneva. The professional journal Physical Review Letters published this work in its latest February 13 issue.

The measurements revealed that the average distance between the halo neutrons and the dense core of the nucleus is 7 femtometers. Thus, the halo neutron is about three times as far from the dense core as is the outermost proton, since the core itself has a radius of only 2.5 femtometers. "This is an impressive direct demonstration of the halo character of this isotope. It is interesting that the halo neutron is thus much farther from the other nucleons than would be permissible according to the effective range of strong nuclear forces in the classical model," explains Nörtershäuser. The strong interaction that holds atoms together can only extend to a distance of between 2 to 3 femtometers. The riddle as to how the halo neutron can exist at such a great distance from the core nucleus can only be resolved by means of the principles of quantum mechanics: In this model, the neutron must be characterized in terms of a so-called wave function. Because of the low binding energy, the wave function only falls off very slowly with increasing distance from the core. Thus, it is highly likely that the neutron can expand into classically forbidden distances, thereby inducing the expansive 'heiligenschein'.

This work was supported by the Helmholtz Association, the GSI Darmstadt and the Federal Ministry of Education and Research (BMBF).

Original publication:
W. Nörtershäuser, D. Tiedemann, M. Žáková, Z. Andjelkovic, K. Blaum, M. L. Bissell, R. Cazan, G. W. F. Drake, Ch. Geppert, M. Kowalska, J. Krämer, A. Krieger, R. Neugart, R. Sánchez, F. Schmidt-Kaler, Z.-C. Yan, D. T. Yordanov, C. Zimmermann
Nuclear Charge Radii of 7,9,10Be and the One-Neutron Halo Nucleus 11Be
Physical Review Letters (Vol.102, No.6), February 13, 2009.

Petra Giegerich | idw
Further information:

More articles from Physics and Astronomy:

nachricht Space radiation won't stop NASA's human exploration
18.10.2017 | NASA/Johnson Space Center

nachricht Study shows how water could have flowed on 'cold and icy' ancient Mars
18.10.2017 | Brown University

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: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>



Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

Latest News

Osaka university researchers make the slipperiest surfaces adhesive

18.10.2017 | Materials Sciences

Space radiation won't stop NASA's human exploration

18.10.2017 | Physics and Astronomy

Los Alamos researchers and supercomputers help interpret the latest LIGO findings

18.10.2017 | Physics and Astronomy

More VideoLinks >>>