Synopsis

Proton Effective Charge Depends on Neutron Population

Physics 17, s65
Experiments comparing neutron-rich cadmium with previous data on a neutron-poor version prove that a key parameter in nuclear calculations depends on the neutron-to-proton ratio.
RIKEN

When calculating properties of heavy nuclei, theorists often focus on a subset of the nucleons (protons and neutrons) and assume that these particles have “effective charges” that somehow compensate for all the nucleons that are ignored. However, choosing the appropriate effective charges can be challenging. Now Andrea Jungclaus of the Institute for the Structure of Matter in Spain and her colleagues have provided the first clear experimental evidence that effective charges depend on isospin—the neutron–proton ratio—and have measured this dependence in an unambiguous way [1]. The new information should improve the accuracy of calculations for heavy, neutron-rich nuclei, for which there is limited experimental data.

The nuclear shell model assigns each nucleon to a single-particle state that is similar to an electron orbital in an atom. Researchers have previously shown that the effective charge is different for different nuclei, but it hasn’t been clear whether the variation was attributable to differences in the orbital configuration of the nuclei or to differences in isospin (or both). Jungclaus and her colleagues isolated the effect of isospin by comparing excited-state properties of cadmium-130 with those measured previously in cadmium-98. These two nuclei have very different numbers of neutrons and thus a large difference in isospin. But they have similar orbital configurations since both have full neutron shells and are just two protons short of having full proton shells.

The researchers observed cadmium-130 nuclei produced when a uranium beam at RIKEN in Japan collided with a beryllium target. They combined shell model calculations and the new data along with previous data to determine an effective proton charge of +1.35 for this neutron-rich nucleus, compared with +1.17 for cadmium-98, suggesting an unexpectedly strong isospin dependence of the effective charge.

–David Ehrenstein

David Ehrenstein is a Senior Editor for Physics Magazine.

References

  1. A. Jungclaus et al., “Excited-state half-lives in 130Cd and the isospin dependence of effective charges,” Phys. Rev. Lett. 132, 222501 (2024).

Subject Areas

Nuclear Physics

Related Articles

Adding Certainty to Plutonium’s Fission Yield
Nuclear Physics

Adding Certainty to Plutonium’s Fission Yield

A first-of-its-kind measurement reveals the energy spectrum of the neutrons produced during the fission of plutonium, a common nuclear fuel component. Read More »

Lanthanum Less Abundant Than Previously Thought
Nuclear Physics

Lanthanum Less Abundant Than Previously Thought

Measurements related to the production of lanthanum in stars where elements are thought to form via the “i process” indicate that less of the element is produced than models predict. Read More »

Making Neutron-Deficient Nuclei
Nuclear Physics

Making Neutron-Deficient Nuclei

Adding neutrinos to an existing nucleosynthesis recipe can account for the puzzling existence of neutron-deficient heavy nuclei. Read More »

More Articles