Browsing by Author "Baker, Stephen D."
Now showing 1 - 14 of 14
Results Per Page
Sort Options
Item A polarization study of the elastic scattering of _He by _He(1968) Hardy, Donald McCoy; Baker, Stephen D.The asymmetries in the elastic scattering of a particles from a 3He target polarized by the technique of optical pumping have been measured at a center of mass scattering angle near 87° in the energy range 4.5 to 9.1 MeV. The qualitiative behavior of the measured asymmetries agrees with that predicted by one of several sets of phase shifts for 4He + 3He elastic scattering.Item A polarized ≥He ion source: Measuring the polarization(1967) Findley, David Owen; Baker, Stephen D.An ion source has been assembled at Rice University which uses the principle of optical pumping to produce polarized He ions for extraction and acceleration. The design of an experiment to measure the degree of polarization of the ions is described. 3He+ ions are accelerated to an energy of approximately 300 keV and produce protons through the 2H(3 He,p) 4He reaction on striking a deuterated target. The polarization of the outgoing protons, measured through the left-right asymmetry of their elastic scattering in a helium-filled polarimeter, provides the information necessary to deduce the nuclear spin polarization of the 3He ions. The polarimeter and its associated equipment are described. The results of tests of the polarimeter system with alpha particles and with unpolarized protons are given.Item A ³He beam polarization monitor(1976) Judd, David Michael; Baker, Stephen D.A polarized 3-He ion source is installed on an injection line of the Texas A & M cyclotron. The polarization is obtained by optically pumping the helium gas. A helium polarimeter was built to constantly monitor the polarization of the ion beam. The design considerations and construction of the polarimeter are discussed. Preliminary experiments have been carried out with the polarimeter; the results of these experiments are discussed.Item An ionization chamber technique for the measurement of the transverse spin dependence of the proton-proton total cross-section(1981) Madigan, William Paul; Phillips, Gerald C.; Mutchler, Gordon S.; Baker, Stephen D.High precision ionization chambers were designed end built to measure the transverse spin dependence of the proton-proton total cross-section difference in the 318 MeV to 8 MeV energy region. Severe microphonic noise was minimized by mounting one of the chambers on pneumatic vibration isolators. Consideration of large fluctuations of the ionization produced in the thin gas layers of the chambers and the measured electronics noise accounts for about 6% of the resolution width of the measurement. Additional effects such as the beam intermittently scraping the target cavity, secondary emission of electrons, and beam-related RF pickup are postulated to account for the remaining width. Designing, constructing, and operation the high-precision ionization chambers has greatly improved our understanding of high-accuracy applications of ionization chambers and analog electronics.Item Analyzing powers and phase shifts in 3He-3He scattering(1976) Biegert, Edward Karl; Baker, Stephen D.Polarization analyzing powers for the elastic scattering of 3He from a polarized 3He target have been measured at three angles for laboratory energies between 8.9 and 34.8 MeV. This includes the 15 to 28 MeV excitation region of 6Be where a broad l = 3 resonance in the elastic scattering differential cross sections has been observed. There is qualitative agreement between these data and a recent resonating group calculation by Reichstein. Minor adjustments in the magnitude of the F wave splitting predicted by Reichstein give good fits to the data. We obtain splittings between about 5° and 1° at 25 MeV incident energy which predict analyzing powers in excess of .4 at certain angles.Item [Delta]+ production in the PP --> PP[pi] [omicron] reaction at 800 MeV(1980) Pepin, Gregory Paul; Mutchler, Gordon S.; Phillips, Gerald C.; Baker, Stephen D.Fifth order differential cross sections have been measured for the reaction during two experiments using the 8 MeV External Proton Beam at the Los Alamos Meson Physics Facility (LAMPF). The kinematically complete data were obtained at seven angular settings covering a range of four-momentum transfers. The protons were detected by MWPC counters on two arms which measured the reaction angles for both charged particles. A magnetic spectrometer measured the momentum of one of the protons. The measured cross sections were compared to calculations using a peripheral model of pion production. Results indicate that the data can be fit with a single value of the pion form factor parameter whose value is much larger than that predicted using optical model calculations.Item Low frequency double electron Muon resonance in fused quartz(1983) Warren, Mial E.; Estle, Thomas L.; Baker, Stephen D.; Dodds, Stanley A.Double Electron Muon Resonance (DEMUR) is a double resonance technique for the study of muonium defect centers in insulators and semiconductors. A DEMUR experiment was performed at a low rf frequency to investigate the response of the muonium coupled spin system to perpendicular static and oscillating fields of comparable magnitude. The experiment was performed in fused quartz with a linearly polarized rf field resonant with the .dm =1 transition of the muonium triplet in a five gauss static field. For small rf field amplitudes, the results were as predicted by a theory consistent with the rotating wave approximation. For rf fields comparable in magnitude to the static field, significant deviations from the theory were observed. A theory for DEMUR with large alternating fields has not been developed.Item Magneto-hydrostatic equilibrium configurations for the magnetosphere of Uranus(1984) Ip, Antonio K.; Wolf, Richard A.; Dunning, F. Barry; Baker, Stephen D.At the time of the Voyager 2 flyby of Uranus, the rotational axis of the planet will be roughly antiparallel to the solar wind flow. If Uranus has a magnetic dipole moment that is approximately aligned with its spin axis, we will have the rare opportunity to observe a ''pole-on'' magnetosphere as discussed qualitatively by Siscoe(1971). Due to the axial symmetry of a pole-on magnetosphere we are able to utilize the Grad-Shafranov theory for calculating a self-consistent magneto-hydrostatic equilibrium model of the magnetosphere of Uranus. In this paper we present an analytic model for the linear case. We also mention an approximation method which enables us to calculate the tail configuration when different relations between the thermal plasma pressure and the vector potential are assumed.Item Self frequency-locking of a dye laser to the center of an atomic transition frequency(1985) Johnson, Lee K.; Jeys, Thomas H.; Walters, G. King; Baker, Stephen D.A new method of passive frequency stabilization is used to lock the laser output frequency to an atomic transition. A Michelson interferometer replaces the output coupler of a broadband standing wave dye laser. A sodium vapor absorber placed in one leg of the interferometer increases feedback only at the absorption frequency, forcing the laser to operate at this frequency. A fully Doppler-broadened vapor Results in simultaneous laser output at the 2S1/2-2P1/2 2S1/2-2P3/2 transition frequencies (dV=52 GHz) with linewidtns of 3 GHz each. An atomic beam of 1 MHz Doppler width produces simultaneous operation on both the [equation] transition frequencies (AV = 1.77 GHz) with linewidths of 1 MHz each. This technique should be applicable to other absorbers and may be of interest in optical pumping applications.Item Spin correlation parameters in [--> over]p-³[--> over]He and [--> over]d-³[--> over]He elastic scattering(1974) May, Donald Philip; Baker, Stephen D.Analyzing powers and spin correlation parameters have been measured for polarized protons elastically scattered from polarized He at energies E^ = 8.82 and 6.8 MeV at ©cm = 39.6°, 76.8°, 19.5°, and 136.8°. The parameters (Oh 72) measured in this experiment were A , A , C , and C . The results of a phase shift search which includes these data are also presented. In addition, analyzing powers and spin correlation parameters have been measured for d- He elastic scattering at energies E, = 3.73 to 11.89 MeV at = 49.5°, 95.3°, and 12.°. In this case a polarized deuteron beam was incident on a polarized He target.Item Spin-polarized low energy electron diffraction studies of Cu¿Au(001)(1985) Lind, David Melvin; Walters, G. King; Dunning, F. Barry; Baker, Stephen D.Combined measurements in low-energy electron diffraction of both intensity and diffracted electron spin-polarization are obtained for Cu,Au(1). Here the use of polarized LEED represents a refinement over standard LEED techniques because additional and complementary data is obtained. In addition, the recent implementation of a spin-modulated polarized electron source allows the rapid and simultaneous acquisition of PLEED I-V and P-V spectra. The order-disorder transition at the Cu,Au(1) surface, near the bulk transition temperature (at Tc=391°C), seems only slightly to affect PLEED profiles. The polarization of the (1) beam has been studied as a function of temperature between room temperature and 44°C. Although significant polarizations were noted, no dramatic transition-dependent polarization changes were found. Temperature dependent changes in the profiles are noted, and may be attributed to standard thermal scattering according to the Debye-Waller factor. In addition, angular studies of the specular diffraction were obtained, and may be used to characterize the ordered state at room temperature.Item Temperature dependence of time resolved (ArXe)+emission(1983) Houston, Louis M.; Walters, G. King; Baker, Stephen D.; Glass, Graham P.Rare gas binary mixtures under electron bombardment are characterized by strong emissions that have been traced to radiative transitions of diatomic heteronuclear ions (e.g.,(ArXej*) .The kinetic processes governing heteronuclear ion formation and decay are not well understood,but the more Important of these processes should be elucidated by time resolved spectroscopy. In particular, since heteronuclear rare gas ions are known to be only weakly bound, their characteristic emissions are expected to be greatly affected by changes in temperature. Under this assumption,an experiment was devised to study the (ArXe)+ 32nm emission under time resolved conditions for different temperatures and mixtures of the gas. The experiment necessitated the design and installation of a temperature variable gas cell. Although the apparatus allows one to vary temperature over a wider range,data,thus far, were taken between 24BK and 348K. In this range, preliminary time dependent spectra have been observed to vary significantly as a function of temperature.Item The elastic scattering of protons from polarized He_(1967) McSherry, Diana Hartridge; Baker, Stephen D.Protonsfrom 3.8 to 10.9 Mev laboratory energy have been elastically scattered from a He3 target polarized by optical pumping). The left-right scattering asymmetries were measured at laboratory angles of 45° and 90°. This data was compared to calculated values of He3 recoil polarization obtained from phase shift analyses using cross section and proton polarization data for the He3(p,p)Re3 reaction. The He3 recoil polarization data is consistent with only one of the four sets of phase shifts which give equally acceptable fits to cross section and proton polarization data.Item Theory of single pion production in nucleon-nucleon scattering(1981) Umland, Eric Alexander; Duck, Ian M.; Baker, Stephen D.; Mutchler, Gordon S.We have developed a phenomenological theory for the reaction NN+NNir based on the peripheral model and the formation and decay of dibaryon resonances. The peripheral graphs include one pion exchange with a monopole form factor at the TTNN vertex and the full TTN elastic scattering amplitude obtained from phase shift analyses and including off-shell corrections. Interfering with the one pion exchange graphs are one rho exchange graphs. Similiar monopole form factors are included at the pNN and pNA vertices. All form factors possess one adjustable parameter. We also study effects due to the still speculative J = 3~ and 2+ dibaryon resonances. The highly inelastic nature of these objects suggests that a single pion production reaction of the form NN+R+NA+NNTr presents the best opportunity for observing dibaryon manifestations. We calculated the fifth order spin dependent differential cross sections d+ (beam polarized up) and cr (beam polarized down) and the asymmetry (c+-c)/(a +). The peripheral model alone gives generally poor agreement with the kinematically-complete, beam polarized data of Hancock. Inclusion of the diproton amplitudes results in a general improvement in the fits, supporting the notion of such resonances in the 3 and 1D2 partial waves of the NN channel.