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At least 721 records · Page 40Linked to original sources
PubMed1993

Universal characteristics of transverse momentum transfer in intermediate energy heavy ion collisions.

A microscopic optical model formalism for estimating momentum transfer in intermediate energy heavy ion collisions predicts universal behavior of the transverse component. In particular, for symmetric systems (Ap = AT) heavier than niobium, it appears that values of P perpendicular/A are independent of the mass and charge of the colliding nuclei and vary only with impact parameter and incident beam energy. This suggests that momentum transfer per nucleon saturates to some limiting value with increasing mass.

Calcium↗
PubMed1994

Bose condensation of nuclei in heavy ion collisions.

Using a fully self-consistent quantum statistical model, we demonstrate the possibility of Bose condensation of nuclei in heavy ion collisions. The most favorable conditions of high densities and low temperatures are usually associated with astrophysical processes and may be difficult to achieve in heavy ion collisions. Nonetheless, some suggestions for the possible experimental verification of the existence of this phenomenon are made.

Elementary Particles↗
PubMed1998

Optical model methods of predicting nuclide production from spallation reactions.

Quantum mechanical optical model methods for calculating isotope production cross sections from the spallation of heavy nuclei by high-energy protons are developed from a modified abrasion-ablation collision formalism. The abrasion step is treated quantum-mechanically as a knockout process which leaves the residual prefragment nucleus in an excited state. In ablation the prefragment deexcites to produce the final fragment. The excitation energies of the prefragments are estimated from a combination of liquid drop and frictional-spectator interaction considerations. Estimates of elemental and isotopic production cross sections are in good agreement with recently published cross section measurements.

Cosmic Radiation↗
PubMed1990

Higgs-boson production in nucleus-nucleus collisions.

Cross-section calculations are presented for the production of intermediate-mass Higgs bosons produced in ultrarelativistic nucleus-nucleus collisions via two-photon fusion. The calculations are performed in position space using Baur's method for folding together the Weizsacker-Williams virtual-photon spectra of the two colliding nuclei. It is found that two-photon fusion in nucleus-nucleus collisions is a plausible way of finding intermediate-mass Higgs bosons at the Superconducting Super Collider or the CERN Large Hadron Collider.

Elementary Particles↗
PubMed1985

Search for anomalous fragments produced in collisions with heavy target nuclei and in delta Z = 1 peripheral interactions.

We exposed a stack of CR39 track detectors containing Ag foils to a 1.7-GeV/nucleon 56Fe beam and investigated the anomalous mean-free-path effect. Neither the whole set of 7517 nor a subset of 2542 interacting fragments produced probably in the Ag target show an effect. By combining the data of this and an earlier experiment we can also exclude an effect for 3219 interacting fragments produced in delta Z = 1 collisions.

Argon↗
PubMed1989

Nuclear collective flow and charged-pion emission in Ne-nucleus collisions at E/A = 800 MeV.

Triple-differential cross sections of charged pions were measured for collisions of Ne projectiles at E/A = 800 MeV with NaF, Nb, and Pb targets. The reaction plane was estimated event by event from the light-baryon momentum distribution. For heavy targets, preferential emission of charged pions away from the interaction zone towards the projectile side was observed in the transverse direction. Such a preferential emission, which is not predicted by cascade calculations, may be attributed to a stronger pion absorption by the heavier spectator remnant.

Elementary Particles↗
PubMed1996

Biological effects of stellar collapse neutrinos

Massive stars in their final stages of collapse radiate most of their binding energy in the form of MeV neutrinos. The recoil atoms that they produce in elastic scattering off nuclei in organic tissue create radiation damage which is highly effective in the production of irreparable DNA harm, leading to cellular mutation, neoplasia, and oncogenesis. Using a conventional model of the galaxy and of the collapse mechanism, the periodicity of nearby stellar collapses and the radiation dose are calculated. The possible contribution of this process to the paleontological record of mass extinctions is examined.

Animals↗
PubMed2000

Linking solar and long baseline terrestrial neutrino experiments.

We show that, in the framework of three light neutrino species with hierarchical masses and assuming no fine tuning between the entries of the neutrino mass matrix, one can use the solar neutrino data to obtain information on the element U(e3) of the lepton mixing matrix. Conversely, a measurement of U(e3) in atmospheric or long baseline accelerator or reactor neutrino experiments would help discriminate between possible oscillation solutions of the solar neutrino problem.

Earth, Planet↗
PubMed2000

Probing possible decoherence effects in atmospheric neutrino oscillations.

It is shown that the results of the Super-Kamiokande atmospheric neutrino experiment, interpreted in terms of nu(mu)<-->nu(tau) flavor transitions, can probe possible decoherence effects induced by new physics (e.g., by quantum gravity) with high sensitivity, supplementing current laboratory tests based on kaon oscillations and on neutron interferometry. By varying the (unknown) energy dependence of such effects, one can either obtain strong limits on their amplitude or use them to find an unconventional solution to the atmospheric nu anomaly based solely on decoherence.

Atmosphere↗
PubMed2001

Simulation of the spherically symmetric stellar core collapse, bounce, and postbounce evolution of a star of 13 solar masses with boltzmann neutrino transport, and its implications for the supernova mechanism.

With exact three-flavor Boltzmann neutrino transport, we simulate the stellar core collapse, bounce, and postbounce evolution of a 13M star in spherical symmetry, the Newtonian limit, without invoking convection. In the absence of convection, prior spherically symmetric models, which implemented approximations to Boltzmann transport, failed to produce explosions. We consider exact transport to determine if these failures were due to the transport approximations made and to answer remaining fundamental questions in supernova theory. The model presented here is the first in a sequence of models beginning with different progenitors. In this model, a supernova explosion is not obtained.

Astronomy↗
PubMed2003

Revised alpha4 term of lepton g-2 from the Feynman diagrams containing an internal light-by-light scattering subdiagram.

The alpha(4) contribution to the lepton g-2 from a gauge-invariant set of 18 Feynman diagrams containing a light-by-light scattering subdiagram internally has been reevaluated by a method independent of the previous approach. Comparison of two methods revealed a program error in the first version. Correcting this error, the contributions of these 18 diagrams become -0.990 72(10)(alpha/pi)(4) and -4.432 43(58)(alpha/pi)(4) for the electron and muon g-2, respectively. The correction is not large enough to affect the comparison between theory and experiment for the muon g-2, but it does alter the inferred value for the fine structure constant alpha(-1) by 6 ppb.

Elementary Particles↗
PubMed1997

Risk assessment for heavy ions of parts tested with protons.

An internuclear cascade-evaporation code is used to model energy deposition in thin slabs of silicon. This model shows that protons produce a significant number of events with effective Linear Energy Transfer (LET) greater than 8 MeV cm2/mg and demonstrates that proton testing of microelectronic components can be an effective way to screen devices for low earth orbit susceptibility to heavy ions.

Computer Simulation↗
PubMed2001

Neutron production from polyethylene and common spacecraft materials.

We report experimental measurements of neutron production from collisions of neutron beams with polyethylene blocks simulating tissue at the Los Alamos National Laboratory Neutron Science Center and 1 GeV/amu iron nuclei with spacecraft shielding materials at the Brookhaven National Laboratory AGS.

Elementary Particle Interactions↗
PubMed1979

Mineral content of skeletal bones in otosclerosis.

In 63 patients with otosclerosis confirmed by operation, the bone mineral content was determined by photon absorptiometry. The bone mineral content and bone mineral concentration were found to be normal, which lends support to the assumption that otosclerosis is a localized disease and not a manifestation of a generalized disorder of the skeletal system.

Absorption↗
PubMed1994

Direct imaging in a water layer of human chromosome fibres composed of nucleosomes and their higher-order structures by laser-plasma X-ray contact microscopy.

X-ray contact microscopy with a 300-ps-duration laser-plasma X-ray source has been used to image hydrated human chromosomes. Clearly imaged are individual nucleosomes and their higher-order particles (superbeads), elementary chromatin fibrils. c. 30 nm in diameter and their higher-order fibres of various sizes up to c. 120 nm in diameter. The results demonstrate that X-ray microscopy is now capable of opening a new path of investigation into the detailed structures of hydrated chromosome fibres in their natural state.

Cells, Cultured↗