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Extended direct semidirect mechanism and the role of multistep processes in fast nucleon radiative capture
We have recently developed an extension of the direct-semidirect (DSD) radiative capture model to unstable final states and have confirmed its utility in explaining the spectrum of rays from capture of polarized 19.6-MeV protons on {sup 89}Y. It was found that the extended DSD model, supplemented by a Hauser-Feshbach contribution, successfully explains the observed spectra, angular distributions, and analyzing powers, without requiring additional mechanisms, such as precompound or multistep emission, or nucleon-nucleon bremsstrahlung. In this contribution we show that the model also successfully explains data at higher energies (34 MeV incident protons), and that there is no need for additional contributions other than Hauser-Feshbach at this energy as well. The extended DSD model treats capture to unbound final states and also to bound single-particle states that damp into a compound system. An optical (complex) potential is used to describe the propagation of the captured particle. Application of this model to the {gamma} spectrum in the {sup 89}Y(p,{gamma} ) reaction at 19.6 MeV is shown. We have performed new calculations at higher energy (34 MeV protons), and have compared them with the spectra and angular distributions measured in [2] on targets of natural Cu, Ag, and Au. An example of the results, for the spectrum from Cu, is shown in the right-hand part of the figure. In both cases the DSD calculation is shown by a solid line, and a Hauser-Feshbach calculation by a dashed line. The 34-MeV calculations were very similar to those at 19.6 MeV as described in [1]. In both cases, the sum of DSD and Hauser-Feshbach calculations adequately describes the measured spectra. Although not shown, the angular distributions are also well described. There are no significant deficiencies in the comparison with experiment that indicate a need for multistep processes or other additional reaction mechanisms. Such processes are therefore required, if at all, only at significantly higher energies than reported here. On the basis of these results, we believe that the extended DSD model is the most appropriate tool for modeling the high-energy portion of the gamma spectrum from nu- cleon capture. On the other hand, simple precompound treatments such as the exciton model should remain important for emission in reactions with complex projectiles (e.g. d, {alpha}, heavy ions), as long as an easily-implemented quantum mechanical model is not available
Fine Structure Discussion of Parity-Nonconserving Neutron Scattering at Epithermal Energies
The large magnitude and the sign correlation effect in the parity
non-conserving resonant scattering of epithermal neutrons from Th is
discussed in terms of a non-collective local doorway model. General
conclusions are drawn as to the probability of finding large parity violation
effects in other regions of the periodic table.Comment: 6 pages, Tex. CTP# 2296, to appear in Z. Phys.
Anomalous anapole moment of an exotic nucleus
Using the information on the nuclear structure of exotic neutron-rich halo
nucleus Be, we evaluate the parity violating anapole moment in its
ground state. The resulting value Be) is fifteen times
bigger than the typical value of the anapole moment of a normal nucleus of the
same mass, and in fact exceeds by few times anapole moments of any known
neutron-odd nuclei (e.g., kappa(^{11}Be) > 2|\kappa(^{207}Pb)|. It is also few
times bigger than the neutral current contribution to the lepton-nucleus
interaction.Comment: 12 pages, 2 figure
Theory of parity violation in compound nuclear states; one particle aspects
In this work we formulate the reaction theory of parity violation in compound
nuclear states using Feshbach's projection operator formalism. We derive in
this framework a complete set of terms that contribute to the longitudinal
asymmetry measured in experiments with polarized epithermal neutrons. We also
discuss the parity violating spreading width resulting from this formalism. We
then use the above formalism to derive expressions which hold in the case when
the doorway state approximation is introduced. In applying the theory we limit
ourselves in this work to the case when the parity violating potential and the
strong interaction are one-body. In this approximation, using as the doorway
the giant spin-dipole resonance and employing well known optical potentials and
a time-reversal even, parity odd one-body interaction we calculate or estimate
the terms we derived. In our calculations we explicitly orthogonalize the
continuum and bound wave functions. We find the effects of orthogonalization to
be very important. Our conclusion is that the present one-body theory cannot
explain the average longitudinal asymmetry found in the recent polarized
neutron experiments. We also confirm the discrepancy, first pointed out by
Auerbach and Bowman, that emerges, between the calculated average asymmetry and
the parity violating spreading width, when distant doorways are used in the
theory.Comment: 37 pages, REVTEX, 5 figures not included (Postscript, available from
the authors
An O(N) symmetric extension of the Sine-Gordon Equation
We discuss an O(N) exension of the Sine-Gordon (S-G)equation which allows us
to perform an expansion around the leading order in large-N result using
Path-Integral methods. In leading order we show our methods agree with the
results of a variational calculation at large-N. We discuss the striking
differences for a non-polynomial interaction between the form for the effective
potential in the Gaussian approximation that one obtains at large-N when
compared to the N=1 case. This is in contrast to the case when the classical
potential is a polynomial in the field and no such drastic differences occur.
We find for our large-N extension of the Sine-Gordon model that the unbroken
ground state is unstable as one increases the coupling constant (as it is for
the original S-G equation) and we determine the stability criteria.Comment: 21 pages, Latex (Revtex4) v3:minor grammatical changes and addition
Riemann's theorem for quantum tilted rotors
The angular momentum, angular velocity, Kelvin circulation, and vortex
velocity vectors of a quantum Riemann rotor are proven to be either (1) aligned
with a principal axis or (2) lie in a principal plane of the inertia ellipsoid.
In the second case, the ratios of the components of the Kelvin circulation to
the corresponding components of the angular momentum, and the ratios of the
components of the angular velocity to those of the vortex velocity are analytic
functions of the axes lengths.Comment: 8 pages, Phys. Rev.
Spin-structures of N-boson systems with nonzero spins - an analytically solvable model with pairing force
A model is proposed to study the possible pairing structures of N-boson
systems with nonzero spin. Analytical solutions have been obtained. The
emphasis is placed on the spin-structures of ground states with attractive or
repulsive pairing force, and with or without the action of a magnetic field. A
quantity (an analogue of the two-body density function) is defined to study the
spin-correlation between two bosons in N-body systems. The excitation of the
system has also been studied.Comment: 10 pages, 2 figures, accepted by Few-Body System
Bias-voltage induced phase-transition in bilayer quantum Hall ferromagnets
We consider bilayer quantum Hall systems at total filling factor in
presence of a bias voltage which leads to different filling factors
in each layer. We use auxiliary field functional integral approach to study
mean-field solutions and collective excitations around them. We find that at
large layer separation, the collective excitations soften at a finite wave
vector leading to the collapse of quasiparticle gap. Our calculations predict
that as the bias voltage is increased, bilayer systems undergo a phase
transition from a compressible state to a phase-coherent state {\it
with charge imbalance}. We present simple analytical expressions for
bias-dependent renormalized charge imbalance and pseudospin stiffness which are
sensitive to the softening of collective modes.Comment: 12 pages, 5 figures. Minor changes, one reference adde
Elastic Scattering of Pions From the Three-nucleon System
We examine the scattering of charged pions from the trinucleon system at a
pion energy of 180 MeV. The motivation for this study is the structure seen in
the experimental angular distribution of back-angle scattering for pi+ 3He and
pi- 3H but for neither pi- 3He nor pi+ 3H. We consider the addition of a double
spin flip term to an optical model treatment and find that, though the
contribution of this term is non-negligible at large angles for pi+ 3He and pi-
3H, it does not reproduce the structure seen in the experiment.Comment: 15 pages + 5 figure
New features of collective motion of intrinsic degrees of freedom. Toward a possible way to classify the intrinsic states
Three exactly solvable Hamiltonians of complex structure are studied in the
framework of a semi-classical approach. The quantized trajectories for
intrinsic coordinates correspond to energies which may be classified in
collective bands. For two of the chosen Hamiltonians the symmetry SU2xSU2 is
the appropriate one to classify the eigenvalues in the laboratory frame.
Connections of results presented here with the molecular spectrum and
Moszkowski model are pointed out. The present approach suggests that the
intrinsic states, which in standard formalisms are heading rotational bands,
are forming themselves "rotational" bands, the rotations being performed in a
fictious boson space.Comment: 33 pages, 9 figure
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