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Register a new userOne-neutron halo structure by the ratio method
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We present a new observable to study halo nuclei. This new observable is a particular ratio of angular distributions for elastic breakup and scattering. For one-neutron halo nuclei, it is shown to be independent of the reaction mechanism and to provide significant information about the structure of the projectile, including binding energy, partial-wave configuration, and radial wave function of the halo. This observable offers new capabilities for the study of nuclear structure far from stability.
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Recently a new observable to study halo nuclei was introduced, based on the ratio between breakup and elastic angular cross sections. This new observable is shown by the analysis of specific reactions to be independent of the reaction mechanism and to provide nuclear-structure information of the projectile. Here we explore the details of this ratio method, including the sensitivity to binding energy and angular momentum of the projectile. We also study the reliability of the method with breakup energy. Finally, we provide guidelines and specific examples for experimentalists who wish to apply this method.
The neutron-rich $^{11}$Li halo nucleus is unique among nuclei with known separation energies by its ability to emit a proton and a neutron in a $beta$ decay process. The branching ratio towards this rare decay mode is evaluated within a three-body model for the initial bound state and with Coulomb three-body final scattering states. The branching ratio should be comprised between two extreme cases, i.e. a lower bound $6 times 10^{-12}$ obtained with a pure Coulomb wave and an upper bound $5 times 10^{-10}$ obtained with a plane wave. A simple model with modified Coulomb waves provides plausible values between between $0.8 times 10^{-10}$ and $2.2 times 10^{-10}$ with most probable total energies of the proton and neutron between 0.15 and 0.3 MeV.
Some one-neutron halo nuclei can emit a proton in a beta decay of the halo neutron. The branching ratio towards this rare decay mode is calculated within a two-body potential model of the initial core+neutron bound state and final core+proton scattering states. The decay probability per second is evaluated for the $^{11}$Be, $^{19}$C and $^{31}$Ne one-neutron halo nuclei. It is very sensitive to the neutron separation energy.
Halo is one of the most interesting phenomena in exotic nuclei especially for $^{31}$Ne, which is deemed to be a halo nucleus formed by a $p-$wave resonance. However, the theoretical calculations dont suggest a $p-$wave resonance using the scattering phase shift approach or complex scaling method. Here, we apply the complex momentum representation method to explore resonances in $^{31}$Ne. We have calculated the single-particle energies for bound and resonant states together with their evolutions with deformation. The results show that the $p-$wave resonances appear clearly in the complex momentum plane accompanied with the $p-f$ inversion in the single-particle levels. As it happens the $p-f$ inversion, the calculated energy, width, and occupation probabilities of major components in the level occupied by valance neutron support a $p-$wave halo for $^{31}$Ne.
The tunneling of composite systems, where breakup may occur during the barrier penetration process is considered in connection with the fusion of halo-like radioactive, neutron- and proton-rich nuclei on heavy targets. The large amount of recent and new data clearly indicates that breakup hinders the fusion at near and below the Coulomb barrier energies. However, clear evidence for the halo enhancements, seems to over ride the breakup hindrance at lower energies, owing, to a large extent, to the extended matter density distribution. In particular we report here that at sub-barrier energies the fusion cross section of the Borromean two-neutron halo nucleus $^{6}$He with the actinide nucleus $^{238}$U is significantly enhanced compared to the fusion of a no-halo $^{6}$He. This conclusion differs from that of the original work, where it was claimed that no such enhancement ensues. This sub-barrier fusion enhancement was also observed in the $^{6}$He + $^{209}$% Bi system. The role of the corresponding easily excitable low lying dipole pygmy resonance in these systems is therefore significant. The consequence of this overall enhanced fusion of halo nuclei at sub-barrier energies, on stellar evolution and nucleosynthesis is evident.
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