Synopsis: Nucleon attractions

High-precision mass measurements of an isotope of mercury will help us to understand the forces between nucleons in nuclei.
Synopsis figure
Illustration: Alan Stonebraker

Comparing the masses of nuclei that differ by a few neutrons or protons can yield empirical values for the interaction strengths between the valence nucleons. By measuring the strength of these interactions, we can better extrapolate the structure of heavier, less stable nuclei to help answer such questions as “Do superheavy nuclei exist?” or “How are heavy elements created?”

One of the most useful nuclear regions in which to carry out these comparisons is around the doubly magic nucleus 208Pb, which has a well-understood shell structure. Unfortunately, the mass of 208Hg, which contains two fewer protons than 208Pb, has not been known to sufficient precision to make meaningful comparisons. A beautiful experiment appearing in Physical Review Letters has now filled in this missing piece. Using the unique capabilities available at the GSI near Darmstadt, Germany, an international team of scientists captured nuclear fragmentation products, including 208Hg, from a high-energy beam of 238U into the Experimental Storage Ring (ESR). Sensitive detectors around the ring measured the circulation frequencies of the different species, which depend on the particle masses.

When combined with previous mass measurements, the new 208Hg mass measurement allows for the first time an empirical determination of the average proton-neutron interaction for neutron orbits above the closed shell at N=126. The interaction strength decreases dramatically beyond the closed shell, confirming that it depends strongly on the spatial overlap of the valence orbits. These new results will help to refine predictions for nuclei far from stability. – Gene D. Sprouse


More Features »


More Announcements »

Subject Areas

Nuclear Physics

Previous Synopsis

Next Synopsis


Fragile state

Read More »

Related Articles

Synopsis: Proton Loses Weight
Particles and Fields

Synopsis: Proton Loses Weight

The most precise measurement to date of the proton mass finds a value that is 3 standard deviations lower than previous estimates. Read More »

Viewpoint: Scattering Experiments Tease Out the Strong Force
Particles and Fields

Viewpoint: Scattering Experiments Tease Out the Strong Force

The scattering of protons from a carbon isotope can be used to test models of the strong force. Read More »

Viewpoint: Getting to the Bottom of an Antineutrino Anomaly
Particles and Fields

Viewpoint: Getting to the Bottom of an Antineutrino Anomaly

The Daya Bay Collaboration reports that sterile neutrinos probably aren’t behind a puzzling deficit in detected antineutrinos at nuclear reactors. Read More »

More Articles