Targeting a Nuclear Halo

Michael Schirber

Synopsis

Targeting a Nuclear Halo

January 4, 2023• Physics 16, s2

New modeling explains the relatively high fusion reaction probabilities of halo nuclei, which are composed of a dense core surrounded by a “satellite” of one or two nucleons.

Certain nuclei have a “halo” made up of one or two nucleons that orbit at a distance from the nuclear core. Such nuclei have a higher probability—or larger “cross section”—of interacting with other nuclei through fusion reactions. To understand the factors behind this enhanced cross section, Xiang-Xiang Sun from the University of the Chinese Academy of Sciences and colleagues have modeled a halo nucleus, carbon-15, and compared it to the haloless nucleus, carbon-14 [1]. They find that two factors play a role in carbon-15’s increased reaction likelihood: its large size and its deformed shape.

Physicists are interested in halo nuclei because their unique structure provides a test bed for nuclear physics theories. “The halo represents one of the most fascinating exotic nuclear properties,” Sun says. Researchers can create these short-lived nuclei in laboratories and study their interactions with other nuclei. Beams of carbon-15 nuclei, for example, have been generated and fired into thorium-232 targets. The outputs suggest that carbon-15 is 2–5 times more likely to fuse with thorium than carbon-14 at energies below the electrostatic (Coulomb) barrier [2].

Sun and colleagues explain the carbon-15 fusion enhancement by modeling the interactions with nuclear time-dependent density functional theory, which tracks the collective motion of the reacting nuclei. The carbon-15 nucleus has a single neutron orbiting a carbon-14-like core. The extended size of the halo leads to a smaller electrostatic repulsion, which means carbon-15 can penetrate deeper into a target nucleus than carbon-14. However, the researchers found that they also had to include direction-dependent effects stemming from carbon-15’s elongated shape. The researchers say their method can be extended to other halo nuclei with more than one orbiting nucleon.

–Michael Schirber

Michael Schirber is the Deputy Editor of Physics Magazine.

References

X. X. Sun and L. Guo, “Microscopic study of fusion reactions with weakly bound nucleus: Effects of deformed halo,” Phys. Rev. C 107, L011601 (2023).
M. Alcorta et al., “Fusion reactions with the one-neutron halo nucleus ¹⁵C,” Phys. Rev. Lett. 106, 172701 (2011).