302 research outputs found
Crossing of two Coulomb-Blockade Resonances
We investigate theoretically the transport of non--interacting electrons
through an Aharanov--Bohm (AB) interferometer with two quantum dots (QD)
embedded into its arms. In the Coulomb-blockade regime, transport through each
QD proceeds via a single resonance. The resonances are coupled through the arms
of the AB device but may also be coupled directly. In the framework of the
Landauer--Buttiker approach, we present expressions for the scattering matrix
which depend explicitly on the energies of the two resonances and on the AB
phase. We pay particular attention to the crossing of the two resonances.Comment: 15 pages, 1 figur
Experimental evidence for 56Ni-core breaking from the low-spin structure of the N=Z nucleus 58Cu
Low-spin states in the odd-odd N=Z nucleus 58Cu were investigated with the
58Ni(p,n gamma)58Cu fusion evaporation reaction at the FN-tandem accelerator in
Cologne. Seventeen low spin states below 3.6 MeV and 17 new transitions were
observed. Ten multipole mixing ratios and 17 gamma-branching ratios were
determined for the first time. New detailed spectroscopic information on the
2+,2 state, the Isobaric Analogue State (IAS) of the 2+,1,T=1 state of 58Ni,
makes 58Cu the heaviest odd-odd N=Z nucleus with known B(E2;2+,T=1 --> 0+,T=1)
value. The 4^+ state at 2.751 MeV, observed here for the first time, is
identified as the IAS of the 4+,1,T=1 state in 58Ni. The new data are compared
to full pf-shell model calculations with the novel GXPF1 residual interaction
and to calculations within a pf5/2 configurational space with a residual
surface delta interaction. The role of the 56Ni core excitations for the
low-spin structure in 58Cu is discussed.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
Spreading Width for Decay out of a Superdeformed Band
The attenuation factor F responsible for the decay out of a superdeformed
(SD) band is calculated with the help of a statistical model. This factor is
given by 1/F = (1 + Gamma(down) / Gamma(S)). Here, Gamma(S) is the width for
the collective E2 transition within the superdeformed band, and Gamma(down) is
the spreading width which describes the mixing between a state in the SD band
and the normally deformed (ND) states of equal spin. The attenuation factor F
is independent of the statistical E1 decay widths Gamma(N) of the ND states
provided that the Gamma(N) are much larger than both Gamma(down) and Gamma(S).
This condition is generically met. Previously measured values of F are used to
determine Gamma(down).Comment: Submitted to Physical Review Letter
Spectral Decorrelation of Nuclear Levels in the Presence of Continuum Decay
The fluctuation properties of nuclear giant resonance spectra are studied in
the presence of continuum decay. The subspace of quasi-bound states is
specified by one-particle one-hole and two-particle two-hole excitations and
the continuum coupling is generated by a scattering ensemble. It is found that,
with increasing number of open channels, the real parts of the complex
eigenvalues quickly decorrelate. This appears to be related to the transition
from power-law to exponential time behavior of the survival probability of an
initially non-stationary state.Comment: 10 Pages, REVTEX, 4 PostScript figure
Strong fragmentation of low-energy electromagnetic excitation strength in Sn
Results of nuclear resonance fluorescence experiments on Sn are
reported. More than 50 transitions with MeV were
detected indicating a strong fragmentation of the electromagnetic excitation
strength. For the first time microscopic calculations making use of a complete
configuration space for low-lying states are performed in heavy odd-mass
spherical nuclei. The theoretical predictions are in good agreement with the
data. It is concluded that although the E1 transitions are the strongest ones
also M1 and E2 decays contribute substantially to the observed spectra. In
contrast to the neighboring even Sn, in Sn the
component of the two-phonon quintuplet built on top of
the 1/2 ground state is proved to be strongly fragmented.Comment: 4 pages, 3 figure
Transition rates and nuclear structure changes in mirror nuclei 47Cr and 47V
Lifetime measurements in the mirror nuclei 47Cr and 47V were performed by
means of the Doppler-shift attenuation method using the multidetector array
EUROBALL, in conjunction with the ancillary detectors ISIS and the Neutron
Wall. The determined transition strengths in the yrast cascades are well
described by full pf shell model calculations.Comment: Latex2e, 11 pages, 3 figure
Search for the electric dipole excitations to the multiplet in Sn
The odd-mass Sn nucleus was investigated in nuclear resonance
fluorescence experiments up to an endpoint energy of the incident photon
spectrum of 4.1 MeV at the bremsstrahlung facility of the Stuttgart University.
More than 50 mainly hitherto unknown levels were found. From the measurement of
the scattering cross sections model independent absolute electric dipole
excitation strengths were extracted. The measured angular distributions
suggested the spins of 11 excited levels. Quasi-particle phonon model
calculations including a complete configuration space were performed for the
first time for a heavy odd-mass spherical nucleus. These calculations give a
clear insight in the fragmentation and distribution of the , , and
excitation strength in the low energy region. It is proven that the
component of the two-phonon quintuplet built on
top of the ground state is strongly fragmented. The theoretical
calculations are consistent with the experimental data.Comment: 10 pages, 5 figure
Chaotic Scattering in Heavy--Ion Reactions
We discuss the relevance of chaotic scattering in heavy--ion reactions at
energies around the Coulomb barrier. A model in two and three dimensions which
takes into account rotational degrees of freedom is discussed both classically
and quantum-mechanically. The typical chaotic features found in this
description of heavy-ion collisions are connected with the anomalous behaviour
of several experimental data.Comment: 35 pages in RevTex (version 3.0) plus 27 PostScript figures
obtainable by anonymous ftp from VAXFCT.CT.INFN.IT in directory kaos. Fig. 1
upon request to the authors. To be published in the October Focus issue on
chaotic scattering of CHAO
A VP3/VP1 gene polymerase chain reaction assay for detection of chicken anemia virus in broiler samples
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