226 research outputs found
Euthria boavistensis Cosel, 1982
Catálogo do Museo de Historia Natural USC. n. inventario 10023
Euthria rolani Cosel, 1982
Catálogo do Museo de Historia Natural USC. n. inventario 10023
Shell-model test of the rotational-model relation between static quadrupole moments Q(2^+_1), B(E2)'s, and orbital M1 transitions
In this work, we examine critically the relation between orbital magnetic
dipole (scissors mode) strength and quadrupole deformation properties. Assuming
a simple K=0 ground state band in an even-even nucleus, the quantities Q(2^+_1)
(i.e., the static quadrupole moment) and B(E2)_{0_1 \to 2_1} both are described
by a single parameter--the intrinsic quadrupole moment Q_0. In the shell model,
we can operationally define Q_0(Static) and Q_0(BE2) and see if they are the
same. Following a brief excursion to the sd shell, we perform calculations in
the fp shell. The nuclei we consider ({44,46,48}Ti and {48,50}Cr) are far from
being perfect rotors, but we find that the calculated ratio
Q_0(Static)/Q_0(BE2) is in many cases surprisingly close to one. We also
discuss the collectivity of orbital magnetic dipole transitions. We find that
the large orbital B(M1) strength in {44}Ti relative to {46}Ti and {48}Ti cannot
be explained by simple deformation arguments.Comment: 12 pages, RevTeX4. Sections II (Quadrupole properties in the
sd-shell) and V (Random interaction studies) added. Minor changes throughout
the text and 48Cr added to present Table IV, as well as results for the
lowest 100 state
Study of the and reactions close to threshold
Two--kaon production in proton--deuteron collisions has been studied at three
energies close to threshold using a calibrated magnetic spectrograph to measure
the final He and a vertex detector to measure the pair.
Differential and total cross sections are presented for the production of
--mesons, decaying through , as well as for prompt
production. The prompt production seems to follow phase space in both
its differential distributions and in its energy dependence. The amplitude for
the {He} reaction varies little for excess energies below 22
MeV and the value is consistent with that obtained from a threshold
measurement. The angular distribution of the decay pair shows that
near threshold the --mesons are dominantly produced with polarization
along the initial proton direction. No conclusive evidence for
production is found in the data.Comment: 13 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
Fine structure of the isoscalar giant quadrupole resonance in 40Ca due to Landau damping?
The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca
has been investigated in high energy-resolution experiments using proton
inelastic scattering at E_p = 200 MeV. Fine structure is observed in the region
of the ISGQR and its characteristic energy scales are extracted from the
experimental data by means of a wavelet analysis. The experimental scales are
well described by Random Phase Approximation (RPA) and second-RPA calculations
with an effective interaction derived from a realistic nucleon-nucleon
interaction by the Unitary Correlation Operator Method (UCOM). In these results
characteristic scales are already present at the mean-field level pointing to
their origination in Landau damping, in contrast to the findings in heavier
nuclei and also to SRPA calculations for 40Ca based on phenomenological
effective interactions, where fine structure is explained by the coupling to
two-particle two-hole (2p-2h) states.Comment: Phys. Lett. B, in pres
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