246 research outputs found
On alfa-particle heating of a thermonuclear plasma
The theory of the slowing down and thermalization of alfa-partides created in and slowed down by a plasma considered as an undisturbed thermal bath is re-examined. The considerations are limited to a homogeneous, isotropic plasma. Also the alfaparticles are considered as a density-wise negligible component of the plasma. Under these circumstances, all essential parts of the theory can be studied analytically. Thus all standard approximations can be studied with precision. However, the conclusions do not differ from numerical results earlier obtained by numerous authors. In this sense the present paper must be considered as a review based on analytical methods. The standard approximations referred to are such as the neglect of the variation of the Coulomb logarithm with velocity, the influence of quantum-mechanical effects, the significance of the impact parameter cut-off (the Debye length), and the assumption of a Maxwellian plasma. Some of these effects have been examined analytically by other authors. However, the present work shows that the Fokker-Planck equation can be solved without the aid of computers for the simplest set of standard approximations. The result thereof is a determination of slowing down rates and rate of growth of energy spread and thereby thermalization of the alfa-particles
Nuclear structure and reaction studies at SPIRAL
The SPIRAL facility at GANIL, operational since 2001, is described briefly.
The diverse physics program using the re-accelerated (1.2 to 25 MeV/u) beams
ranging from He to Kr and the instrumentation specially developed for their
exploitation are presented. Results of these studies, using both direct and
compound processes, addressing various questions related to the existence of
exotic states of nuclear matter, evolution of new "magic numbers", tunnelling
of exotic nuclei, neutron correlations, exotic pathways in astrophysical sites
and characterization of the continuum are discussed. The future prospects for
the facility and the path towards SPIRAL2, a next generation ISOL facility, are
also briefly presented.Comment: 48 pages, 27 figures. Accepted for publication in Journal of Physics
Standard Model tests with trapped radioactive atoms
We review the use of laser cooling and trapping for Standard Model tests,
focusing on trapping of radioactive isotopes. Experiments with neutral atoms
trapped with modern laser cooling techniques are testing several basic
predictions of electroweak unification. For nuclear decay, demonstrated
trap techniques include neutrino momentum measurements from beta-recoil
coincidences, along with methods to produce highly polarized samples. These
techniques have set the best general constraints on non-Standard Model scalar
interactions in the first generation of particles. They also have the promise
to test whether parity symmetry is maximally violated, to search for tensor
interactions, and to search for new sources of time reversal violation. There
are also possibilites for exotic particle searches. Measurements of the
strength of the weak neutral current can be assisted by precision atomic
experiments using traps of small numbers of radioactive atoms, and sensitivity
to possible time-reversal violating electric dipole moments can be improved.Comment: 45 pages, 17 figures, v3 includes clarifying referee comments,
especially in beta decay section, and updated figure
Nonlinear wave interaction in coastal and open seas -- deterministic and stochastic theory
We review the theory of wave interaction in finite and infinite depth. Both of these strands of water-wave research begin with the deterministic governing equations for water waves, from which simplified equations can be derived to model situations of interest, such as the mild slope and modified mild slope equations, the Zakharov equation, or the nonlinear Schr\"odinger equation. These deterministic equations yield accompanying stochastic equations for averaged quantities of the sea-state, like the spectrum or bispectrum. We discuss several of these in depth, touching on recent results about the stability of open ocean spectra to inhomogeneous disturbances, as well as new stochastic equations for the nearshore
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