Influence of halo single-neutron transfer on near barrier $$^{15}$$C + $$^{12}$$C total fusion

A recent comparison of the average fusion cross section, $$\left\langle \sigma _\mathrm {F}\right\rangle $$ σ F , for energies just above the Coulomb barrier for the $$^{12-15}$$ 12 - 15 C + $$^{12}$$ 12 C systems found that the behaviour as a function of projectile neutron excess could not be satisfactorily explained by static barrier penetration model calculations and suggested that the neutron dynamics plays an important rôle. In this work we demonstrate that the ($$^{15}$$ 15 C,$$^{14}$$ 14 C) single neutron transfer has a significant influence on the above barrier $$^{15}$$ 15 C + $$^{12}$$ 12 C total fusion, although not quite in the way expected since it leads to a reduction in the cross section, contrary to the trend in the measured $$\left\langle \sigma _\mathrm {F}\right\rangle $$ σ F . However, this result underlines the danger of ignoring the effect of neutron transfer reactions on fusion in systems involving neutron halo nuclei.

Halo Properties in Helium Nuclei from the Perspective of Geometrical Thermodynamics

The nuclear matter and charge radii of the helium isotopes (A = 4,6,8) are calculated by quantitative geometrical thermodynamics (QGT) taking as input the symmetry of the alpha-particle, the very weak binding (and hence halo nature) of the heavier helium isotopes, and a characteristic length scale given by the proton size. The results follow by considering each isotope in its ground state, with QGT representing each system as a maximum entropy configuration that conforms to the Holographic Principle. This allows key geometric parameters to be determined from the number of degrees of freedom available. QGT treats 6He as a 4He core plus a concentric neutron shell comprising a holomorphic pair of neutrons, and the 8He neutron halo is treated as a holomorphic pair of holomorphic pairs. Considering the information content of each system allows a correlation angle of 2pi/3 between the holomorphic entities to be inferred, and then the charge radii of the three isotopes can be calculated from the displacement of the 4He core from the centre of mass. The calculations for the charge and matter radii of 4,6,8He agree closely with observed values. Similar QGT calculation of the sizes of the self-conjugate A = 4n nuclei {4He,8Be,12C,16O,20Ne,24Mg,28Si,32S,36Ar,40Ca} also agree well with experiment.