268 research outputs found
An interferometric study of dissociative recombination radiation in neon and argon afterglows
Spectral line profiles on neon and argon determined by high resolution, photoelectric recording, pressure tuned Fabry-Perot interferomete
A mathematical study of the electron decay in diffusion and recombination controlled afterglows - Annals of physics
Mathematical solution for electron continuity equation in decaying plasma afterglo
On the alternatives for bath correlators and spectral densities from mixed quantum-classical simulations
We investigate on the procedure of extracting a "spectral density" from mixed
QM/MM calculations and employing it in open quantum systems models. In
particular, we study the connection between the energy gap correlation function
extracted from ground state QM/MM and the bath spectral density used as input
in open quantum system approaches. We introduce a simple model which can give
intuition on when the ground state QM/MM propagation will give the correct
energy gap. We also discuss the role of higher order correlators of the
energy-gap fluctuations which can provide useful information on the bath.
Further, various semiclassical corrections to the spectral density, are applied
and investigated. Finally, we apply our considerations to the photosynthetic
Fenna-Matthews-Olson complex. For this system, our results suggest the use of
the Harmonic prefactor for the spectral density rather than the Standard one,
which was employed in the simulations of the system carried out to date.Comment: 21 pages, 16 figure
Theory of collision-induced translation-rotation spectra: H2-He
This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.29.595.An adiabatic quantal theory of spectral line shapes in collision-induced absorption and emission is presented which incorporates the induced translation-rotation and translation-vibration spectra. The generalization to account for the anisotropy of the scattering potential is given. Calculations are carried out of the collision-induced absorption spectra of He in collisions with H2 with ab initio electric dipole functions and realistic potentials. The anisotropy of the interaction potential is small and is not included in the calculations. The predicted spectra are in satisfactory agreement with experimental data though some deviations occur which may be significant. The rotational line shapes have exponential wings and are not Lorentzian. The connection between the quantal and classical theories is written out explicitly for the isotropic overlap induction
Cooperative damping mechanism of the resonance in the nuclear photoabsorption
We propose a resonance damping mechanism to explain the disappearance of the
peaks around the position of the resonances higher than the resonance
in the nuclear photoabsorption. This phenomenon is understood by taking into
account the cooperative effect of the collision broadening of and
, the pion distortion and the interference in the two-pion
photoproduction processes in the nuclear medium.Comment: 11 pages, uses revtex.sty. To appear in Phys. Rev. Let
Photofission of heavy nuclei at energies up to 4 GeV
Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and
natPb have been measured simultaneously, using tagged photons in the energy
range Egamma=0.17-3.84 GeV. This was the first experiment performed using the
Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the
photofission cross section for 238U relative to that for 237Np is about 80%,
implying the presence of important processes that compete with fission. We also
observe that the relative photofission cross sections do not depend strongly on
the incident photon energy over this entire energy range. If we assume that for
237Np the photofission probability is equal to unity, we observe a significant
shadowing effect starting below 1.5 GeV.Comment: 4 pages of RevTex, 6 postscript figures, Submitted to Phys. Rev. Let
Evaluation of the total photoabsorption cross sections for actinides from photofission data and model calculations
We have calculated the fission probabilities for 237-Np, 233,235,238-U,
232-Th, and nat-Pb following the absorption of photons with energies from 68
MeV to 3.77 GeV using the RELDIS Monte-Carlo code. This code implements the
cascade-evaporation-fission model of intermediate-energy photonuclear
reactions. It includes multiparticle production in photoreactions on
intranuclear nucleons, pre-equilibrium emission, and the statistical decay of
excited residual nuclei via competition of evaporation, fission, and
multifragmentation processes. The calculations show that in the GeV energy
region the fission process is not solely responsible for the entire total
photoabsorption cross section, even for the actinides: ~55-70% for 232-Th,
\~70-80% for 238-U, and ~80-95% for 233-U, 235-U, and 237-Np. This is because
certain residual nuclei that are created by deep photospallation at GeV photon
energies have relatively low fission probabilities. Using the recent
experimental data on photofission cross sections for 237-Np and 233,235,238-U
from the Saskatchewan and Jefferson Laboratories and our calculated fission
probabilities, we infer the total photoabsorption cross sections for these four
nuclei. The resulting cross sections per nucleon agree in shape and in
magnitude with each other. However, disagreement in magnitude with
total-photoabsorption cross-section data from previous measurements for nuclei
from C to Pb calls into question the concept of a ``Universal Curve'' for the
photoabsorption cross section per nucleon for all nuclei.Comment: 39 pages including 11 figure
Photofission and Quasi-Deuteron-Nuclear State as Mixing of Bosons and Fermions
The empirical-phenomenological quasi-deuteron photofission description is
theoretically justified within the semiclassical, intermediate statistics
model. The transmutational fermion (nucleon) - boson (quasi-deuteron) potential
plays an essential role in the present context and is expressed in terms of
thermodynamical and of microscopical quantities, analogous to those commonly
used in the superfluid nuclear model.Comment: 7 pages, RevTex, to appear in Zeit. f. Phys.
The Role of Nucleons in Electromagnetic Emission Rates
Electromagnetic emission rates from a thermalized hadronic gas are important
for the interpretation of dilepton signals from heavy-ion collisions. Although
there is a consensus in the literature about rates for a pure meson gas,
qualitative differences appear with a finite baryon density. We show this to be
essentially due to the way in which the pi-N background is treated in regards
to the nucleon resonances. Using a background constrained by unitarity and
broken chiral symmetry, it is emphasized that the thermalized hadronic gas can
be considered dilute.Comment: 9 pages, 7 figures, minor change
- …