186 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
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
Nuclear Photoabsorption at Photon Energies between 300 and 850 Mev
We construct the formula for the photonuclear total absorption cross section
using the projection method and the unitarity relation. Our treatment is very
effective when interference effects in the absorption processes on a nucleon
are strong. The disappearance of the peak around the position of the
resonance in the nuclear photoabsorption can be explained with the cooperative
effect of the interference in two-pion production processes,the Fermi motion,
the collision broadenings of and , and the pion distortion in the
nuclear medium. The change of the interference effect by the medium plays an
important role.Comment: 22pages,7figures,revtex
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
A magnetic field diagnostic for sonoluminescence
This study is motivated by the extraordinary process of single bubble
sonoluminescence (SBSL), where an acoustically driven spherical shock is
thought to power the emitted radiation. We propose new experiments using an
external magnetic field which can induce anisotropies in both the shock
propagation and radiation pattern. The effects will depend on the temperature,
conductivity, and size of the radiating region. Our predictions suggest that
such a laboratory experiment could serve as an important diagnostic in placing
bounds on these parameters and understanding the physics of sonoluminescence.Comment: Latex File, Two .eps files, 5 pages, submitted to PR
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.
Theory of quantum radiation observed as sonoluminescence
Sonoluminescence is explained in terms of quantum radiation by moving
interfaces between media of different polarizability. In a stationary
dielectric the zero-point fluctuations of the electromagnetic field excite
virtual two-photon states which become real under perturbation due to motion of
the dielectric. The sonoluminescent bubble is modelled as an optically empty
cavity in a homogeneous dielectric. The problem of the photon emission by a
cavity of time-dependent radius is handled in a Hamiltonian formalism which is
dealt with perturbatively up to first order in the velocity of the bubble
surface over the speed of light. A parameter-dependence of the zero-order
Hamiltonian in addition to the first-order perturbation calls for a new
perturbative method combining standard perturbation theory with an adiabatic
approximation. In this way the transition amplitude from the vacuum into a
two-photon state is obtained, and expressions for the single-photon spectrum
and the total energy radiated during one flash are given both in full and in
the short-wavelengths approximation when the bubble is larger than the
wavelengths of the emitted light. It is shown analytically that the spectral
density has the same frequency-dependence as black-body radiation; this is
purely an effect of correlated quantum fluctuations at zero temperature. The
present theory clarifies a number of hitherto unsolved problems and suggests
explanations for several more. Possible experiments that discriminate this from
other theories of sonoluminescence are proposed.Comment: Latex file, 28 pages, postscript file with 3 figs. attache
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