1,537 research outputs found

### Calculation of exciton densities in SMMC

We develop a shell-model Monte Carlo (SMMC) method to calculate densities of
states with varying exciton (particle-hole) number. We then apply this method
to the doubly closed-shell nucleus 40Ca in a full 0s-1d-0f-1p shell-model space
and compare our results to those found using approximate analytic expressions
for the partial densities. We find that the effective one-body level density is
reduced by approximately 22% when a residual two-body interaction is included
in the shell model calculation.Comment: 10 pages, 4 figure

### Monte Carlo Simulation of Quantum Computation

The many-body dynamics of a quantum computer can be reduced to the time
evolution of non-interacting quantum bits in auxiliary fields by use of the
Hubbard-Stratonovich representation of two-bit quantum gates in terms of
one-bit gates. This makes it possible to perform the stochastic simulation of a
quantum algorithm, based on the Monte Carlo evaluation of an integral of
dimension polynomial in the number of quantum bits. As an example, the
simulation of the quantum circuit for the Fast Fourier Transform is discussed.Comment: 12 pages Latex, 2 Postscript figures, to appear in Proceedings of the
IMACS (International Association for Mathematics and Computers in Simulation)
Conference on Monte Carlo Methods, Brussels, April 9

### Atomic final-state interactions in tritium decay

We calculate the effect of the Coulomb interaction of the ejected β ray with the bound atomic electron in the β decay of a tritium atom. The excited state probabilities of the residual helium ion are changed by at most 0.17% from the usual sudden approximation

### Skyrme-force time-dependent Hartree-Fock calculations with axial symmetry

We discuss axially symmetric time-dependent Hartree-Fock calculations using a finite-range modification of the Skyrme energy functional. The finite-difference forms of the coordinate-space time-dependent Hartree-Fock equations, the method of time evolution, and other numerical aspects are presented. Detailed results for (^84)Kr-induced deep-inelastic collisions with (^208)Pb at E_(lab) = 494 MeV and with (^209)Bi at E_(lab) = 600 MeV and 714 MeV are compared with experiment.
[NUCLEAR REACTIONS (^84)Kr + (^208)Pb at E_lab = 494 MeV and (^84)Kr + (^209)Bi at E_1ab=600 and 714 MeV, in the time-dependent Hartree-Fock approximation. Strongy
damped collisions. Details of Skyrme force calculations with axial symmetry.

### Spin-Polarization Response Functions in High-Energy (e,e'p) Reactions

Spin-polarization response functions are examined for high-energy
$(\vec{e},e'\vec{p})$ reaction by computing the full 18 response functions for
the proton kinetic energy $T_{p'}=$ 0.515 GeV and 3.179 GeV with an 16O target.
The Dirac eikonal formalism is applied to account for the final-state
interactions. The formalism is found to yield the response functions in good
agreement with those calculated by the partial-wave expansion method at 0.515
GeV. We identify the response functions that depend on the spin-orbital
potential in the final-state interactions, but not on the central potential.
Dependence on the Dirac- or Pauli-type current of the nucleon is investigated
in the helicity-dependent response functions, and the normal-component
polarization of the knocked-out proton, $P_n$, is computed.Comment: 22 pages, Latex, figures available at
ftp://ftp.krl.caltech.edu/pub/users/rseki/it

### Shell Model Monte Carlo Methods

We review quantum Monte Carlo methods for dealing with large shell model
problems. These methods reduce the imaginary-time many-body evolution operator
to a coherent superposition of one-body evolutions in fluctuating one-body
fields; the resultant path integral is evaluated stochastically. We first
discuss the motivation, formalism, and implementation of such Shell Model Monte
Carlo (SMMC) methods. There then follows a sampler of results and insights
obtained from a number of applications. These include the ground state and
thermal properties of {\it pf}-shell nuclei, the thermal and rotational
behavior of rare-earth and $\gamma$-soft nuclei, and the calculation of double
beta-decay matrix elements. Finally, prospects for further progress in such
calculations are discussed

### Atomic screening of nuclear transitions

In the analysis of time-reversal and Mössbauer absorption experiments, it is important to consider atomic processes which interfere with the direct nuclear transition. Interaction of the photon with the atomic electrons causes the radiation to acquire a phase shift, specified by the interference parameter ξ(L_π). We present theoretical expressions for ξ and compare our calculated values with experiment. Satisfactory agreement is obtained. In particular, an apparent violation of time-reversal invariance in the 129-keV transition of ^(191)Ir is fully explained by these effects

### Coupling of phonons to a helium atom adsorbed on graphite

We compute the self-energy for a ^4He atom adsorbed on graphite to second order in the phonon coupling. The phonon contributions amount to several degrees Kelvin. The imaginary part corresponds to a lifetime of some 10^(-11) s

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