3,439 research outputs found
Radioactive beams and inverse kinematics: probing the quantal texture of the nuclear vacuum
The properties of the quantum electrodynamic (QED) vacuum in general, and of
the nuclear vacuum (ground) state in particular are determined by virtual
processes implying the excitation of a photon and of an electron--positron pair
in the first case and of, for example, the excitation of a collective
quadrupole surface vibration and a particle--hole pair in the nuclear case.
Signals of these processes can be detected in the laboratory in terms of what
can be considered a nuclear analogue of Hawking radiation. An analogy which
extends to other physical processes involving QED vacuum fluctuations like the
Lamb shift, pair creation by rays, van der Waals forces and the
Casimir effect, to the extent that one concentrates on the eventual outcome
resulting by forcing a virtual process to become real, and not on the role of
the black hole role in defining the event horizon. In the nuclear case, the
role of this event is taken over at a microscopic, fully quantum mechanical
level, by nuclear probes (reactions) acting on a virtual particle of the zero
point fluctuation (ZPF) of the nuclear vacuum in a similar irreversible,
no--return, fashion as the event horizon does, letting the other particle,
entangled with the first one, escape to infinity, and eventually be detected.
With this proviso in mind one can posit that the reactions
H(Be,Be;3.37 ))H and
H(Li,Li(; 2.69 ))H together with the
associated decay processes indicate a possible nuclear analogy of
Hawking radiation
Characterization of vorticity in pygmy resonances and soft-dipole modes with two-nucleon transfer reactions
The properties of the two-quasiparticle-like soft E1-modes and PDR have been
and are systematically studied with the help of inelastic and electromagnetic
experiments which essentially probe the particle-hole components of these
vibrations. It is shown that further insight in their characterisation can be
achieved with the help of two-nucleon transferreactions, in particular
concerning the particle-particle components of the modes, in terms of absolute
differential cross sections which take properly into account successive and
simultaneous transfer mechanisms corrected for non-orthogonality, able to
reproduce the experimental findings at the 10% level. The process
LiLi(1) is discussed, and absolute cross sections
predicted.Comment: Typo corrected with respect to previous versio
The 9Li(d,p) reaction, a specific probe of 10Li, paradigm of parity--inverted nuclei around N=6 closed shell
We show, within the framework of renormalized nuclear field theory and of the
induced reaction surrogate formalism, that the highly debated Li
structure, observed in a recent Li(d,p)Li one--neutron transfer
experiment is consistent with or better, requires the presence of a virtual
state of similar single--particle strength than that of the
resonance at 0.45 0.03 MeV. Based on continuum spectroscopy self-energy
techniques, we find that the physical mechanism responsible for parity
inversion in Li is the same as that at the basis of the similar
phenomenon observed in Be and to that needed in Li to have an
important --wave ground state component. Furthermore, it is also consistent
with the (normal) sequence of the and levels in the
isotones B and C.Comment: Revised text and figures. The paper includes supplemental materia
One- and two- neutron halo at the dripline. From 11Be to 11Li and back: 10Li and parity inversion
The nuclei 11Be and 11Li provide paradigmatic examples of one-and two-
neutron halo systems. Because the reaction 1H(11Li,9Li)3H is dominated by
successive transfer, one can use the quantitative picture emerging from a nu-
clear field theory description of the structure and reaction mechanism of the
above Cooper pair transfer process and of the 2H(10Be,11Be)1H and
1H(11Be,10Be)2H reactions, to shed light on the structure of 10Li. This
analysis provides important support for a parity inverted scenario with a 1/2+
virtual state at about 0.2 MeV.Comment: Proceedings of the 15th Varenna Conference on Nuclear Reaction
Mechanism
Structure and reactions of 11Be: many-body basis for single-neutron halo
The exotic nucleus 11Be has been extensively studied and much experimental
information is available on the structure of this system. Treating, within the
framework of empirically renormalised nuclear field theory in both
configuration and 3D-space, the mixing of bound and continuum single-particle
states through the coupling to collective particle-hole (p,h) and pairing
vibrations of the 10Be core, as well as Pauli principle acting not only between
the particles explicitly considered and those participating in the collective
states, but also between fermions involved in two-phonon virtual states it is
possible, for the first time, to simultaneously and quantitatively account for
the energies of the 1/2+,1/2- low-lying states, the centroid and line shape of
the 5/2+ resonance, the one-nucleon stripping and pickup absolute differential
cross sections involving 11Be as either target or residual nucleus, and the
dipole transitions connecting the 1/2+ and 1/2- parity inverted levels as well
as the charge radius, thus providing a unified and exhaustive characterisation
of the many-body effects which are at the basis of this paradigmatic
one-neutron halo system.Comment: Supplemental materials include
The halo of the exotic nucleus 11Li: a single Cooper pair
If neutrons are progressively added to a normal nucleus, the Pauli principle
forces them into states of higher momentum. When the core becomes
neutron-saturated, the nucleus expels most of the wavefunction of the last
neutrons outside to form a halo, which because of its large size can have lower
momentum. It is an open question how nature stabilizes such a fragile system
and provides the glue needed to bind the halo neutrons to the core. Here we
show that this problem is similar to that of the instability of the normal
state of an electron system at zero temperature solved by Cooper, solution
which is at the basis of BCS theory of superconductivity. By mimicking this
approach using, aside from the bare nucleon-nucleon interaction, the long
wavelength vibrations of the nucleus Li, the paradigm of halo nuclei, as
tailored glues of the least bound neutrons, we are able to obtain a unified and
quantitative picture of the observed properties of Li.Comment: 16 pages, 1 b/w figures, 2 colour figure
Surface location of sodium atoms attached to He-3 nanodroplets
We have experimentally studied the electronic excitation of
Na atoms attached to He droplets by means of laser-induced fluorescence as
well as beam depletion spectroscopy. From the similarities of the spectra
(width/shift of absorption lines) with these of Na on He droplets, we
conclude that sodium atoms reside in a ``dimple'' on the droplet surface. The
experimental results are supported by Density Functional calculations at zero
temperature, which confirm the surface location of sodium on He droplets,
and provide a microscopic description of the ``dimple'' structure.Comment: 4 pages, 5 figure
Spin and density longitudinal response of quantum dots in time-dependent local-spin-density approximation
The longitudinal dipole response of a quantum dot has been calculated in the
far-infrared regime using local spin density functional theory. We have studied
the coupling between the collective spin and density modes as a function of the
magnetic field. We have found that the spin dipole mode and single particle
excitations have a sizeable overlap, and that the magnetoplasmon modes can be
excited by the dipole spin operator if the dot is spin polarized. The frequency
of the dipole spin edge mode presents an oscillation which is clearly filling
factor () related. We have found that the spin dipole mode is especially
soft for even values, becoming unstable for magnetic fields in the region
. Results for selected number of electrons and confining
potentials are discussed. An analytical model which reproduces the main
features of the microscopic spectra has been developed.Comment: We have added some new references and minor changes on the mnuscript
have been mad
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