Uncertainties In Direct Neutron Capture Calculations Due To Nuclear Structure Models

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. For spherical nuclei close to the dripline the statistical model (Hauser-Feshbach) approach is not applicable and direct contributions may dominate the cross sections. For neutron-rich, even-even Sn targets, we compare the resulting neutron capture cross sections when consistently taking the input for the direct capture calculations from three different microscopic models. The results underline the sensitivity of cross sections calculated in the direct model to nuclear structure models which can lead to high uncertainties when lacking experimental information.Comment: 4 pages, using espcrc1.sty, Proc. Intl. Conf. "Nuclei in the Cosmos IV", Univ. Notre Dame 1996, Nucl. Phys. A, in press. A postscript version can also be obtained from http://quasar.physik.unibas.ch/research.htm

Observing Nucleon Decay in Lead Perchlorate

Lead perchlorate, part of the OMNIS supernova neutrino detector, contains two nuclei, 208Pb and 35Cl, that might be used to study nucleon decay. Both would produce signatures that will make them especially useful for studying less-well-studied neutron decay modes, e.g., those in which only neutrinos are emitted.Comment: 6 pages, 2 figure

The Path to Improved Reaction Rates for Astrophysics

This review focuses on nuclear reactions in astrophysics and, more specifically, on reactions with light ions (nucleons and alpha particles) proceeding via the strong interaction. It is intended to present the basic definitions essential for studies in nuclear astrophysics, to point out the differences between nuclear reactions taking place in stars and in a terrestrial laboratory, and to illustrate some of the challenges to be faced in theoretical and experimental studies of those reactions. The discussion revolves around the relevant quantities for astrophysics, which are the astrophysical reaction rates. The sensitivity of the reaction rates to the uncertainties in the prediction of various nuclear properties is explored and some guidelines for experimentalists are also provided.Comment: 100 pages, 33 figures, 1 table; accepted for publication in Int. J. Mod. Phys. E (scheduled for February 2011 issue); the formatting here differs in that it includes a table of contents and numbered paragraphs 5.4.2.1-5.4.2.10; v2: updated references; v3: typos fixed; v4: final typo fix, content similar to published version

Dynamical density functional theory for interacting Brownian particles: stochastic or deterministic?

We aim to clarify confusions in the literature as to whether or not dynamical density functional theories for the one-body density of a classical Brownian fluid should contain a stochastic noise term. We point out that a stochastic as well as a deterministic equation of motion for the density distribution can be justified, depending on how the fluid one-body density is defined -- i.e. whether it is an ensemble averaged density distribution or a spatially and/or temporally coarse grained density distribution.Comment: 10 pages, 1 figure, to be submitted to Journal of Physics A: Mathematical and Genera

Performance of the ATLAS Muon Drift-Tube Chambers at High Background Rates and in Magnetic Fields

The ATLAS muon spectrometer uses drift-tube chambers for precision tracking. The performance of these chambers in the presence of magnetic field and high radiation fluxes is studied in this article using test-beam data recorded in the Gamma Irradiation Facility at CERN. The measurements are compared to detailed predictions provided by the Garfield drift-chamber simulation programme

Thermonuclear Ti-42(p, gamma)V-43 rate in type-I x-ray bursts

The thermonuclear rate of the Ti-42(p, gamma)V-43 reaction has been reevaluated based on a recent precise proton separation energy measurement of S-p(V-43) = 83 +/- 43 keV. The astrophysical impact of our new rates has been investigated through one-zone postprocessing type-I x-ray burst calculations. It shows that the new experimental value of S-p significantly affects the yields of species for A approximate to 40-45. As well, the precision of the recent experimental S-p value constrains these yields to better than a factor of 3.Peer reviewedFinal Accepted Versio

Performance of the ATLAS Precision Muon Chambers under LHC Operating Conditions

For the muon spectrometer of the ATLAS detector at the large hadron collider (LHC), large drift chambers consisting of 6 to 8 layers of pressurized drift tubes are used for precision tracking covering an active area of 5000 m2 in the toroidal field of superconducting air core magnets. The chambers have to provide a spatial resolution of 41 microns with Ar:CO2 (93:7) gas mixture at an absolute pressure of 3 bar and gas gain of 2?104. The environment in which the chambers will be operated is characterized by high neutron and background with counting rates of up to 100 per square cm and second. The resolution and efficiency of a chamber from the serial production for ATLAS has been investigated in a 100 GeV muon beam at photon irradiation rates as expected during LHC operation. A silicon strip detector telescope was used as external reference in the beam. The spatial resolution of a chamber is degraded by 4 ?m at the highest background rate. The detection efficiency of the drift tubes is unchanged under irradiation. A tracking efficiency of 98% at the highest rates has been demonstrated