54 research outputs found
Pygmy dipole resonance in exotic nuclei
The evolution of the PDR strength with the neutron excess is investigated in
Sn isotopic and N=82 isotonic chains with regard to its possible connection
with the neutron skin thickness. For this purpose a recently proposed method
incorporating both HFB and multi-phonon QPM theory is applied. Analysis of the
corresponding neutron and proton dipole transition densities is presented.Comment: International Workshop on Nuclear Physics 28th Course - Radioactive
Beams, Nuclear Dynamics and Astrophysics, Ettore Majorana Center for
Scientific Cultur
Probing the Nuclear Neutron Skin by Low-Energy Dipole Modes
Dipole excitations below the neutron threshold in neutron rich Sn isotopes
are studied theoretically in the Quasiparticle-Phonon Model with HFB single
particle input. Of special interest are the low-lying two-phonon 1- states and
the Pygmy Dipole Resonance (PDR). The evolution of low-energy dipole
excitations with neutron excess is investigated over the Sn isotopic chain
including the experimentally unknown regions close to 132Sn. A dependence of
the PDR strengths and centroid energies on the neutron skin thickness is found.
Despite significant multi-phonon contributions to mean energies and transition
strengths, the PDR states retain their one-phonon character. The fragmentation
pattern is reduced with increasing neutron excess towards the N=82 shell
closure which will be of advantage for future experimental work.Comment: 4 pages, 2 figure
Pygmy Dipol Resonances as a Manifestation of the Structure of the Neutron-Rich Nuclei
Dipole excitations in neutron-rich nuclei below the neutron threshold are
investigated. The method is based on Hartree-Fock-Bogoliubov (HFB) and
Quasiparticle-Phonon Model (QPM) theory. Of our special interest are the
properties of the low-lying 1- Pygmy Resonance and the two-phonon
quadrupole-octupole 1- states in Sn-isotopes including exploratory
investigations for the experimentally unknown mass regions. In particular we
investigate the evolution of the dipole strength function with the neutron
excess. The use of HFB mean-field potentials and s.p. energies is found to
provide a reliable extrapolation into the region off stability.Comment: 8 pages, 3 figures, Proceedings of the International Conference on
Collective Motion in Nuclei Under Extreme Conditions (COMEX1), Paris, France,
10-13 June 200
Kabul Times (November 9, 1967, vol. 6, no. 184)
Recent experimental findings and theoretical approaches to the electric dipole (El) strength distribution below the particle emission threshold at shell closures are revisited. Results from photon scattering experiments are discussed and compared to predictions within the quasiparticle-phonon nuclear model. An analysis of the fine structure of the El strength is presented. Recent studies of the E1 response of light exotic nuclei are also discussed
Low-lying GT(+) strength in Co-64 studied via the Ni-64(d,He-2)Co-64 reaction
The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a 171-MeV deuteron beam. An energy resolution of about 110 keV was achieved. In addition to the J(pi) = 1(+) ground state, several other 1(+) states could be identified in Co-64 and the strengths of the corresponding Gamow-Teller transitions were determined. The obtained strength distribution was compared with theoretical predictions and former (n,p) experimental results and displayed a good agreement. Due to the good energy resolution, detailed spectroscopic information was obtained, which supplements the data base needed for network calculations for supernova scenarios
Low-Energy Universality in Atomic and Nuclear Physics
An effective field theory developed for systems interacting through
short-range interactions can be applied to systems of cold atoms with a large
scattering length and to nucleons at low energies. It is therefore the ideal
tool to analyze the universal properties associated with the Efimov effect in
three- and four-body systems. In this "progress report", we will discuss recent
results obtained within this framework and report on progress regarding the
inclusion of higher order corrections associated with the finite range of the
underlying interaction.Comment: Commissioned article for Few-Body Systems, 47 pp, 16 fig
Structure of â·He studied with the â·Li(d,ÂČHe) reaction
A search for the JÏ = 1/2â» spinâorbit partner of the JÏ = 3/2â» ground state in â·He has been performed with the â·Li(d,ÂČHe) charge-exchange reaction. The results are incompatible with recent claims of such a state at very low excitation energy [Meister M et al 2002 Phys. Rev. Lett. 88 102501] but rather suggest a resonance with parameters Ex = (1.2âșâ°.â”ââ.â) MeV, Î = (1.9âșâ°.âžââ.â) MeV. GT strengths deduced for the transitions to the lowest states in 7He are in remarkable agreement with ab initio quantum Monte Carlo calculations
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Gamow-Teller Strength in the A=14 Multiplet: A Challenge to the Shell Model
A new experimental approach to the famous problem of the anomalously slow Gamow-Teller (GT) transitions in the {beta} decay of the A = 14 multiplet is presented. The GT strength distributions to excited states in {sup 14}C and {sup 14}O was studied in high-resolution (d,{sup 2}He) and ({sup 3}He,t) charge-exchange reactions on {sup 14}N. No-core shell-model (NCSM) calculations capable of reproducing the suppression of the {beta} decays predict a selective excitation of J{sup {pi}} = 2{sup +} states. The experimental confirmation represents a validation of the assumptions about the underlying structure of the {sup 14}N ground state wave function. However, the fragmentation of the GT strength over three 2{sup +} final states remains a fundamental issue not explained by the present NCSM using a 6 {h_bar}{omega} model space, suggesting possibly the need to include cluster structure in these light nuclei in a consistent way
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