Presence Of Heavy Nuclei Research Articles

Nucleus-acoustic shock waves in white dwarfs

The nucleus-acoustic shock waves (NASWs) propagating in a white dwarf plasma system, which contain non-relativistically or ultrarelativistically degenerate electrons, non-relativistically degenerate, viscous fluid of light nuclei, and immobile nuclei of heavy elements, have been theoretically investigated. We have used the reductive perturbation method, which is valid for small but finite-amplitude NASWs to derive the Burgers equation. The NASWs are, in fact, associated with the nucleus-acoustic (NA) waves in which the inertia is provided by the light nuclei, and restoring force is provided by the degenerate pressure of electrons. On the other hand, the stationary heavy nuclei participate only in maintaining the background charge neutrality condition at equilibrium. It is found that the viscous force acting in the fluid of light nuclei is a source of dissipation, and is responsible for the formation of NASWs. It is also observed that the basic features (polarity, amplitude, width, etc.) of the NASWs are significantly modified by the presence of heavy nuclei, and that NASWs are formed with either positive or negative potential depending on the values of the charge density of the heavy nuclei. The basic properties are also found to be significantly modified by the effects of ultrarelativistically degenerate electrons. The implications of our results in white dwarfs are briefly discussed.

Cosmic-ray secondary antiprotons - A closer look

view Abstract Citations (109) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmic-Ray Secondary Antiprotons: A Closer Look Gaisser, Thomas K. ; Schaefer, Robert K. Abstract Following a suggestion of Webber that early calculations underestimated the intensity of secondary anti-protons, we have systematically reexamined three aspects of the calculation: the normalization and shape of the present interstellar spectrum, nuclear enhancement of antiproton production in collisions involving nuclei, and the mean energy-dependent residence time of secondary nuclei and antiprotons in the Galaxy. In particular, we have a new estimate of the nuclear enhancement factor, based on the wounded nucleon model. Here we find that the presence of heavy nuclei in the cosmic rays increases the antiproton flux by only 20% over a pure proton composition. We conclude that the reported experimental values of the antiproton-to-proton ratio of Ep ≈ 6-12 GeV remain significantly above the range of theoretical expectation allowed by uncertainties in the input assumptions. Publication: The Astrophysical Journal Pub Date: July 1992 DOI: 10.1086/171568 Bibcode: 1992ApJ...394..174G Keywords: Antiprotons; Cosmic Rays; Nuclear Astrophysics; Astronomical Spectroscopy; Computational Astrophysics; Interstellar Matter; Space Radiation; ELEMENTARY PARTICLES; ISM: COSMIC RAYS full text sources ADS |

Formation and signature of quark matter in relativistic ion collisions

Exclusively using experimental information on particle production in nucleon-nucleon interactions, this paper attempts to demonstrate that: (i) the characteristics of relativistic collisions between heavy nuclei are determined by quark physics, not conventional nuclear physics; (ii) the formation of quark matter in such collisions can be observed experimentally via large multiplicities, copious production of photons (not from π decay), the anomalous strangeness, charm and baryon number structure of the events, and appearance of structure in the rapidity distribution; (iii) the formation of quark matter has actually been observed in high energy cosmic ray interactions. We show that the 100 TeV threshold for the appearance of anomalous interactions reflects the transition from nucleonic to quark structure of the nucleus. Observed anomalies match the signatures of quark matter formation in (ii); (iv) our results imply the abundant presence of heavy nuclei, e.g. Fe, in the high energy cosmic ray spectrum. Cosmic ray interactions above 100 TeV can eventually be used to study the vacuum structure of quantum chromodynamics and the disappearance of spontaneous symmetry breaking due to the restoration of symmetry at high matter densities.

Radiative Processes in the Presence of Heavy Nuclei

Calculations of the cross sections for bremsstrahlung and pair production are carried out without the use of the Born approximation, but by reducing the calculation of these cross sections to the calculation of the exact elastic scattering of electrons and positrons, the last quantities having been tabulated to some extent. Large deviations from the Born approximation results are obtained in the angular distributions of these radiative processes, but arguments are presented that the Born approximation should yield the integrated cross sections correctly at sufficiently high energies. The failure of the Born approximations for relativistic equations is explained in a purely classical way.