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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
441

Nuclear structure, nuclear reaction

Etchegoyen, Maria Cristina Berisso de January 1982 (has links)
In this thesis, particle- particle angular correlations for reactions in non-zero degree geometry and with non-zero spin nuclei are performed and found to be a valuable tool for spin determination, (d-α) angular correlations in the reaction process <sup>14</sup>N(<sup>6</sup>Li,d)<sup>18</sup>F* (α)<sup>14</sup>N are measured for three high excited states in <sup>18</sup>F with a <sup>6</sup>Li beam of 36MeV. Spins and parities for two of the observed states are determined, and in agreement with theoretical predictions, these states are suggested as members of the K<sup>π</sup>=1<sup>+</sup> α-rotational band. The three analysed 9.58MeV 6<sup>+</sup>, 11.2MeV, 14.1MeV 8<sup>+</sup> states are found to undergo a predominant α-particle decay to the ground state of <sup>14</sup>N. Gamow unbound formalism is carried out for the state descriptions. Angular distributions are measured and analysed under Hauser Feshbach and exact finite range DWBA formalisms. Spectroscopic factors are extracted and compared to shell model predictions, showing a reasonable agreement. (<sup>3</sup>He-α) and (t-α) angular correlations for the reaction processes <sup>14</sup>N(<sup>6</sup>Li,<sup>3</sup>He)<sup>17</sup>0* (α)<sup>13</sup>C and <sup>14</sup>N(<sup>6</sup>Li,t)<sup>17</sup>F* (α)<sup>13</sup>N respectively are measured at 36MeV of <sup>6</sup>Li. High selectivity is observed for the three particle transfer processes and percentages of the different particle decays for the high populated states are presented. Structureless angular correlations hinder definite spin and parity assignements, but the displacement of the preferred direction observed in the pattern decay gives some information on the range of plausible angular momenta. Shell model calculations are performed for comparison with the experimental data, and this allows tentative spin identifications. EFR EWEA calculations are carried out, providing some confirmation on the spin suggestions. Useful nuclear structure information is obtained for the mass 17 and 18 nuclear states. The particle-particle angular correlation expression for a process where a direct reaction mechanism is involved is reviewed, programmed and used for obtaining the theoretical predictions to be compared to the experimental results.
442

Van de Graaff based positron source production

Lund, Kasey Roy 04 November 2015 (has links)
<p> The anti-matter counterpart to the electron, the positron, can be used for a myriad of different scientific research projects to include materials research, energy storage, and deep space flight propulsion. Currently there is a demand for large numbers of positrons to aid in these mentioned research projects. There are different methods of producing and harvesting positrons but all require radioactive sources or large facilities. Positron beams produced by relatively small accelerators are attractive because they are easily shut down, and small accelerators are readily available. </p><p> A 4MV Van de Graaff accelerator was used to induce the nuclear reaction <sup> 12</sup>C(d,n)<sup>13</sup>N in order to produce an intense beam of positrons. 13N is an isotope of nitrogen that decays with a 10 minute half life into <sup>13</sup>C, a positron, and an electron neutrino. This radioactive gas is frozen onto a cryogenic freezer where it is then channeled to form an antimatter beam. The beam is then guided using axial magnetic fields into a superconducting magnet with a field strength up to 7 Tesla where it will be stored in a newly designed Micro-Penning-Malmberg trap. </p><p> Several source geometries have been experimented on and found that a maximum antimatter beam with a positron flux of greater than 0.55&times;10<sup> 6</sup> e+s<sup>-1</sup> was achieved. This beam was produced using a solid rare gas moderator composed of krypton. Due to geometric restrictions on this set up, only 0.1-1.0% of the antimatter was being frozen to the desired locations. Simulations and preliminary experiments suggest that a new geometry, currently under testing, will produce a beam of 107 e+s<sup>-1</sup> or more.</p>
443

Statistical hadronization phenomenology in heavy ion collisions at SPS and RHIC energies

Torrieri, Giorgio January 2004 (has links)
This dissertation examines the phenomenology of statistical hadronization at ultrarelativistic energies. We start with an overview of current experimental and theoretical issues in Relativistic heavy ion physics. We then introduce statistical hadronization, and show how it gives a description of particle abundances and spectra through relativistic covariance and entropy maximization. We argue that several statistical hadronization models are possible; In particular, a distinction can be made between equilibrated staged freeze-out in which post-formation hadron interactions play an important role in determining final-state observables, and non-equilibrium sudden freeze-out where spectra and abundances get determined at the same time and further interactions are negligible. We attempt to falsify sudden freeze-out by examining whether particle abundances and spectra can be described using the same formation temperature. This is done both in the chemical equilibrium framework, and using a chemical non-equilibrium ansatz. Our fits to experimental data suggest that the sudden freeze-out model explains both the particle abundances and spectra. We then try to extract the particle formation temperature, and quantify post-freeze-out hadronic interactions using experimentally observable resonances. We discuss observed resonances and suggest further measurements that have the potential to distinguish between the possible freeze-out scenarios experimentally. Finally, we infer from experimental data how particle formation proceeds in spacetime, in particular whether freeze-out dynamics agrees with the sudden freeze-out expectation. We examine particle spectra, and show that they are not sensitive enough to pick the right freeze-out dynamics. We suggest resonances and azimuthal anisotropy as experimental probes for this task.
444

Rapidity dependence of the single inclusive jet cross section in proton-antiproton collisions at the center-of-mass energy of 1.8 TeV with the Dzero detector

Babukhadia, Levan January 1999 (has links)
We have made a precise measurement of the rapidity dependence of inclusive single jet production cross section d²s/dE(T)dη in pp̄ collisions at √s=1.8 TeV. The measurement is based on integrated luminosity of 92 pb⁻¹ data collected by the D⊘ detector at the Tevatron Collider, Fermi National Accelerator Laboratory. The cross sections are reported as a function of jet transverse energy in five pseudorapidity (η) intervals up to η = 3.0. The experimental results are in good agreement with the theoretical predictions from next-to-leading order perturbative quantum chromodynamics.
445

Heavy quark production in heavy-ion collisions

Valerio, Peter Michael, 1968- January 1996 (has links)
The results of the full next-to-leading-order calculation of open charm production cross section, via hard parton scattering, for both hadronic and heavy-ion collisions at RHIC and LHC energies are presented. In addition to the total cross section, the transverse momentum and rapidity distributions are included. An effective K-factor which encapsulates the next-to-leading-order corrections and the nuclear effects is presented. The open charm yield will be measured through the correlated dileptons produced when the charm decays. An important background comes from the decay of bottom quarks. Therefore, the open bottom yield from hard parton scatterings is presented. The first next-to-leading-order calculation of the thermal heavy quark production is presented, as well as the dimuon spectrum from both the thermal and the initial fusion charm and bottom production at RHIC energies.
446

Kinematic fitting of detached vertices

Mattione, Paul January 2007 (has links)
The eg3 experiment at the Jefferson Lab CLAS detector aims to determine the existence of the &Xgr;5 pentaquarks and investigate the excited &Xgr; states. Specifically, the exotic X--5 pentaquark will be sought by first reconstructing the X- particle through its weak decays, X- &rarr; pi- and &Lgr; &rarr; ppi -. A kinematic fitting routine was developed to reconstruct the detached vertices of these decays, where confidence level cuts on the fits are used to remove background events. Prior to fitting these decays, the exclusive reaction gammaD&rarr; pppi- was studied in order to correct the track measurements and covariance matrices of the charged particles. The &Lgr; &rarr; ppi- and xi- &rarr; pi -&Lgr; decays were then investigated to demonstrate that the kinematic fitting routine reconstructs the decaying particles and their detached vertices correctly.
447

Spin effects in inclusive Lambda production using 200 GeV polarized protons

Nguyen, Chau January 1991 (has links)
We have used the Fermilab Polarized Proton Beam Facility to measure the Analyzing Power and the Depolarization parameters of the inclusive reaction p$\uparrow$ + p $\to$ $\Lambda$ + X. The $\Lambda$ Polarization was also observed as a consistency check against existing data. The kinematic range of the accepted $\Lambda$'s centers at $x\sb{F}$ = 0.5 and $p\sb{t}$ = 0.6 $GeV/c$, with $x\sb{F}$ reaching up to 0.8 and $p\sb{T}$ up to 1.1 $GeV/c$. The Polarization was found to be consistent with previous measurements. The Analyzing Power and Depolarization were found to be near zero at all kinematics bins and in agreement with the only set of existing data which were measured at much lower energies. Beam energy independency was confirmed. The results from our $\Lambda$ data do not contradict predictions made by the Thomas precession model which implies that the proton's spin is carried by the valence quarks.
448

Particle identification by TOF for heavy ion interactions

Chiou, Chengnan January 1990 (has links)
The purpose of the relativistic heavy-ion experiment E810 at the Brookhaven National Laboratory Alternating Gradient Synchrotron(BNL AGS) is to look for indications of a phase transition from hadronic to quark matter: the Quark-Gluon Plasma(QGP). The experiment was performed using a 14.5 $\times$ A Gev/c silicon beam from the BNL AGS to bombard targets of Si, Cu, Sn, Au, and Pb. The experimental apparatus used in the June 1989 run were the BNL Multi-Particle Spectrometer(MPS), the Time Projection Chamber(TPC) system, and the Time-of-Flight(TOF) hodoscope. With a 15m flight path, to separate $\pi\sp-$ from p up to 5-6 Gev/c and $\pi\sp-$ from $k\sp-$ up to 2.5-3 Gev/c, we require that the Root-Mean-Square(RMS) time resolution of the TOF hodoscope be about 150 picoseconds. From the analysis of the TOF beta distribution of fast $\pi\sp-$, a RMS time resolution range of 150-160 ps can be achieved after the time-walk correction.
449

Multinuclei coherent effects on the widths and energy shifts on low energy neutron resonance

Hu, Xiaomin January 1993 (has links)
The exponentially decaying semi-stationary states of an assembly of identical classical radiators can have decay rates and resonant frequencies significantly different from that of an isolated radiator. These coherent effects on classical radiators emitting classical waves apply also to the particle processes in quantum limits, leading to the superradiant and subradiant modes with widths(decay rates) greatly enhanced or suppressed and resonant energies significantly shifted. The purpose of this thesis is to investigate these coherent effects on slow neutron-heavy nuclei interaction. A simple field model is introduced to show the coherent effects on the decay rates and resonant energies of two identical decaying states and on the neutron widths and resonant energies of neutron-two nuclei scattering. The latter case is also obtained by multiple scattering theory and is extended to a more general case of neutron-N nuclei scattering. The coherent effects on neutron width near Bragg angle in a crystal are also investigated.
450

Charge division in a cylindrical drift chamber for E1097

Gaussiran, Thomas Louis, II January 1991 (has links)
A review of the key concepts in the operation of a drift chamber are given. The equations governing charge division are developed. In order to optimize the chamber geometry, calculations were performed so that a suitable geometry for the chamber could be chosen. Electronics to determine position information along the wire (charge division) from the pulses at the two ends of the wire were designed and constructed. A test chamber was constructed and used to demonstrate the validity of the calculations as well as the ability of the electronics to make the position measurement. Results from tests using cosmic rays demonstrate position resolution to have a $\sigma$ of less than 4 mm.

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