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The Study of The Pressure Dependence of Foreign Gas on the Fluorescence of Nitric OxideLai, Chin-Min 31 July 2001 (has links)
The photoabsorption cross sections of NO have been measured in the wavelength range 150~200nm, and the cross sections deviation from Beer-Lambert law due to the insufficient resolution of light source is discussed qualitatively.
From the steady state approximation of quenching reactions, the pressure dependence of foreign gas on the ratio of absorption intensity to the fluorescence intensity is derived. Furthermore, the non-Stern-Volmer behaviors of the C2£S(n=0) state of NO were discussed by assuming the non-predissociated (J<9/2) and the predissociated (J>9/2) rotational levels following different quenching mechanisms.
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Methods for the calculation of cross-sections of interest to nuclear reactor designStreet, A. M. January 1987 (has links)
No description available.
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A Calculation of the Kaon-Neutron Scattering Cross SectionHooper, Robert Gibson 06 1900 (has links)
The purpose of this investigation was to study the scattering processes of K+ mesons with neutrons. In order to do such a study one must first make certain basic assumptions about the type of interaction involved and then proceed to calculate physically meaningful qualities which describe the processes. Thus, the problem is this: assuming the validity of Feynman's rules for these strongly interacting particles, calculate the differential and total scattering cross sections for the interaction of scalar K+ mesons and neutrons.
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A measurement of Z(vv̄)[photon] cross section and limits on anomalous triple gauge couplings at [square root of]s = 7 TeV using CMSShrestha, Shruti January 1900 (has links)
Doctor of Philosophy / Department of Physics / Yurii Maravin / In this thesis, the first measurement of Z(vv̄)[photon] cross section in pp collisions at [square root of]s = 7 TeV has been done using data collected by the CMS detector. The measured cross section is 21.3 ± 4.2 (stat.) ± 4.3 (syst.) ± 0.5 (lumi.) fb. This measurement is based on the observations of events with missing transverse energy in excess of 130 GeV and photon in the rapidity range [eta] < 1.44 of transverse momentum in excess of 145 GeV in a data sample corresponding to an integrated luminosity of 5 fb⁻¹. This measured cross section is in good agreement with the theoretical prediction of 21.9 ± 1.1 fb from BAUR. Further, neutral triple gauge couplings involving Z bosons and photons have been studied. No evidence for the presence of such couplings is observed and is in agreement with the predictions of the standard model. We set the most stringent limits to date on these triple gauge couplings.
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Flux-limited Diffusion Coefficient Applied to Reactor AnalysisKeller, Steven Ede 09 July 2007 (has links)
A new definition of the diffusion coefficient for use in reactor physics calculations is evaluated in this thesis. It is based on naturally flux-limited diffusion theory (FDT), sometimes referred to as Levermore-Pomraning diffusion theory. Another diffusion coefficient more loosely based on FDT is also evaluated in this thesis. Flux-limited diffusion theory adheres to the physical principle of flux-limiting, which is that the magnitude of neutron current is not allowed to exceed the scalar flux. Because the diffusion coefficients currently used in the nuclear industry are not flux-limited they may violate this principle in regions of large spatial gradients, and because they encompass other assumptions, they are only accurate when used in the types of calculations for which they were intended.
The evaluations were performed using fine-mesh diffusion theory. They are in one spatial dimension and in 47, 4, and 2 energy groups, and were compared against a transport theory benchmark using equivalent energy structures and spatial discretization.
The results show that the flux-limited diffusion coefficient (FD) outperforms the standard diffusion coefficient in calculations of single assemblies with vacuum boundaries, according to flux- and eigenvalue-errors. In single assemblies with reflective boundary conditions, the FD yielded smaller improvements, and tended to improve only the fast-group results. The results also computationally confirm that the FD adheres to flux-limiting, while the standard diffusion coefficient does not.
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Measurement of spallation residuals in mercury for accelerator facility targetsBlaylock, Dwayne Patrick 27 May 2016 (has links)
A benchmark experiment was designed and conducted that irradiated two small volume mercury targets at the Weapon Neutron Research facility at the Los Alamos Neutron Science Center with 800 MeV protons. Following irradiation the production cross sections of 53 medium and longer-lived spallation residuals using gamma spectroscopy at various decay times up to a year were determined. The measured cross sections were then compared with predicted cross sections from the MCNPX code. After acquisition of the gamma spectroscopy data the targets were drained and disassembled to study the distribution and the deposition of the spallation residuals.
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Underground study of the 17 O(p,γ )18F reaction at Gamow energies for classical novaeScott, David Andrew January 2014 (has links)
Classical novae are explained as thermonuclear explosions on the surface of white dwarf stars accreting hydrogen-rich material from less evolved companions in binary star systems. These events occur frequently within our galaxy and have been proposed as significant contributors to the galactic abundance of 13C, 15N, 17/18O and 18/19F. The short-lived isotope 18F (t1/2 = 110 min) is of particular importance since it may provide a signature of novae events through the detection of 511 keVγ-ray emission following the β+ decay of a 18F nucleus. During classical novae the 17O(p,γ)18F reaction governs the production of 18F and affects the synthesis of the rare isotopes mentioned above. Prior to the present study, the 17O(p,γ)18F reaction rate was poorly determined owing to a lack of low-energy experimental data. The present work reports on the first accurate measurements of the resonant and non-resonant contributions to the 17O(p,γ)18F reaction cross section in the energy region relevant for classical novae. Measurements were performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) accelerator facility of the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. Here the γ-ray background is suppressed by up to 3 orders of magnitude, thus providing a unique environment for low-energy measurements of reaction cross sections. Prompt γ rays associated with the formation and decay of states in 18F were analysed to determine the resonant and non-resonant contributions to the reaction cross section. The total non-resonant S-factor was determined at energies between Ecm ≈ 200 - 370 keV and the strength of a key resonance at Ecm = 183 keV was obtained with the best precision to date. The uncertainty in the reaction rate is now sufficiently low to place firmer constraints on nucleosynthesis predictions from accurate models of novae.
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Top quark pair production measurements in the single lepton channel using the ATLAS detectorBielski, Rafal January 2018 (has links)
Three measurements of top-quark pair production cross sections in proton-proton collisions at sqrt(s) = 13 TeV using data collected by the ATLAS experiment are presented. The single-lepton final states are used, where one electron or muon, two b-jets and two other jets can be identified. The inclusive ttbar production cross section is measured to be sigma(ttbar) = 817 +/- 13 (stat.) +/- 103 (syst.) +/- 88 (lum.) pb, which is in good agreement with predictions and with other measurements. Absolute and relative differential cross sections of ttbar production are also measured, showing an overall good agreement with predictions, except for the top-quark transverse momentum distribution. As already reported in measurements at lower proton-proton collision energies, this distribution is shifted towards higher momenta in all predictions with respect to the observations. Total and differential fiducial cross sections of ttbar production in association with heavy-flavour jets are also presented. All tested models are found to agree with data within the uncertainties of these measurements.
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Systematics of cross sections for target K-vacancy production in heavy ion collisionsPeng, Yong 25 April 2007 (has links)
Cross sections for K-shell ionization by heavy ions have been determined from the
measurements of target K x-ray yields. The measurements were performed with Ar, Kr,
and Xe ions at energies from 2.5 to 25 MeV/amu and self-supported metallic foil targets
of Al, Ti, Cu, Zr, Ag, Sm, and Ta. The x-ray yields were measured with a Si(Li)
detector, while the projectile ions were counted in coincidence with the x-rays using a
plastic scintillation detector. In addition, the amount of secondary K-shell ionization and
the degree of simultaneous L-shell ionization in primary K-shell ionizing collisions were
assessed by performing high-resolution x-ray measurements on targets of Al, Ti, V, Co,
and Cu with a curved crystal spectrometer.
The results of the high resolution measurements revealed that the apparent average Lshell
spectator vacancy fraction at the time of Kñ x-ray emission, L p , may be represented
by a universal function of the Geometrical ModelâÂÂs parameter X for Z2 = 17 - 32.
Multiple-vacancy Kñ fluorescence yields and corrections for K-shell ionization by
secondary processes were determined with the aid of the high resolution spectra for the targets Al, Ti, and Cu. Fluorescence yields for the other targets were determined using
an extrapolation procedure.
The resulting K-vacancy production cross sections for 2.5 to 6 MeV/amu projectiles
were compared with a limited amount of available experimental data and shown to be in
relatively good agreement.
The ECPSSR predictions for all the targets except Al agreed reasonably well with
experimental cross sections for Ar projectiles. The experimental cross sections for Kvacancy
production in Al, Ti, Cu, Zr, and Ag were greatly deviated from the ECPSSR
predictions. The cross sections for Kr on Sm and Ta were in good agreement with
theory.
The scaling properties of the Kñ x-ray production cross sections were examined and a
semiempirical âÂÂuniversalâ curve was deduced that reproduces the measured cross
sections to within ñ30% on average.
The relationship between the Kñ x-ray production cross sections and the geometrical
modelâÂÂs universal variable also was examined.
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Development of a graphical user interface for the coarse mesh radiation transport code COMET and cross section generation with HELIOSHolcomb, Andrew M. 12 January 2015 (has links)
The coarse mesh radiation transport (COMET) code uses response functions to solve the neutron transport equation. Most nuclear codes used today have a very steep learning curve; COMET is no exception. To ease the user's onus of learning how to create correctly formatted COMET input-files, a graphical user interface (GUI) was created. The GUI allows the user to select values for all the relevant variables while simultaneously minimizing the errors a typical new user would make. To this end, the GUI creates all of the input files required to run COMET. The GUI also provides a visualization tool that the user may use to check the problem geometry before running COMET. The GUI is also responsible for post-processing the COMET output for visualization with TecPlot.
In addition to the GUI, multi-group cross section libraries were generated as part of the MHTGR-350 (Modular High Temperature Gas Reactor) benchmark problem under development at Georgia Tech. This project aims to couple COMET with a thermal hydraulics code to best model the true physics of the reactor design. In order for this goal to be actualized, six-group cross sections were generated over the operational temperature range of the MHTGR using the current coupling and collision probability code HELIOS.
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