Results are presented from an analysis of the particle multiplicity between high transverse energy jets in {anti p}-p collisions at {radical}s = 1,800 GeV. The data were collected using the D0 Detector at Fermi National Accelerator Laboratory. The authors observe an excess of events at low multiplicity which is consistent with strongly interacting color-singlet exchange. The fraction of events due to color-singlet exchange is measured as a function of the transverse energy and rapidity separation of the jets and is compared to several theoretical models for color-singlet exchange.

We have searched for evidence of supersymmetry with the Collider Detector at Fermilab using trilepton events in p{anti p} collisions at {radical}s = 1.8 TeV. In the Minimal Supersymmetric Standard Model (MSSM), we expect trilepton events from chargino-neutralino ({tilde {xi}}{sup {+-}}{sub 1}{tilde {xi}}{sup 0}{sub 2}) pair production, with subsequent decay into leptons. In all possible combinations of electron and muon channels, we observe no candidate events in 107 pb{sup -1} of data. We present limits on chargino and neutralino production within the framework of a supergravity inspired MSSM: {sigma}{sub {tilde {xi}}{sup {+-}}{sub 1}{tilde {xi}}{sup 0}{sub 2}} {center_dot} BR({tilde {xi}}{sup {+-}}{sub 1}{tilde {xi}}{sup 0}{sub 2} {yields} 3l + X) < 0.34 pb and M{sub {tilde {xi}}{sup {+-}}{sub 1}} > 81.5 GeV/c{sup 2} for tan {beta} = 2, {mu} = -600 GeV/c{sup 2} and M{sub {tilde q}} = M{sub {tilde g}}. We also present limits on a SU(5) x U(1) supergravity model and a 4 and 1/2 parameter Minimal SUGRA model.

One-dimensional (1D) and two-dimensional (2D) arrays of Al islands linked by submicron Al/Al{sub x}O{sub y}/Al tunnel junctions were fabricated on an insulating layer grown on a ground plane. The arrays were cooled to temperatures as low as 20 mK where the Josephson coupling energy E{sub J} of each junction and the charging energy E{sub C} of each island were much greater than the thermal energy k{sub B}T. The capacitance C{sub g} between each island and the ground plane was much greater than the junction capacitance C. Two classes of arrays were studied. In the first class, the normal state tunneling resistance of the junctions was much larger than the resistance quantum for single electrons, R{sub N}{much_gt} R{sub Q{sub e}}{identical_to} h/e{sup 2} {approx} 25.8 k{Omega}, and the islands were driven normal by an applied magnetic field such that E{sub J} = 0 and the array was in the Coulomb blockade regime. The arrays were made on degenerately-doped Si, thermally oxidized to a thickness of approximately 100 nm. The current-voltage (I - V) characteristics of a 1D and a 2D array were measured and found to display a threshold voltage V{sub T} below which little current flows. In the second class of …

There has been continuing development of generic classes of microstrip gas chambers (MSGCs), microgap gas chambers (MGCs) and microdot gas chambers (MDOTs) at Lawrence Berkeley National Laboratory (LBNL) over the past few years, to improve such detectors beyond their present capabilities, to produce detectors suitable for use in current or upcoming experiments, and to allow a basis for new R&D developments which may incorporate these detectors as part of the system. All of these new detectors are collectively referred to as {open_quotes}gas avalanche microdetectors{close_quotes}. The MSGC, which was motivated by the pioneering work of A. Oed, has many attractive features, especially excellent spatial resolution ({approximately}30 {mu}m rms at normal incidence) and high rate capability ({approximately}10{sup 6} mm{sup -2}{center_dot}s{sup -1}). Moreover, the MGC seems to have certain advantages over the MSGC in speed, stability and simplicity, and the MDOT has larger gain (>10{sup 4}) and the intrinsic advantages of two-dimensional readout. Because of these attractive properties, they have received a great deal of attention for nuclear and high energy physics experiments, medical X-ray imaging and many other fields requiring radiation detection and measurement.

Microdosimetry was used to investigate three issues at the neutron therapy facility (NTF) at Fermilab. Firstly, the conversion factor from absorbed dose in A-150 tissue equivalent plastic to absorbed dose in ICRU tissue was determined. For this, the effective neutron kerma factor ratios, i.e. oxygen tissue equivalent plastic and carbon to A-150 tissue equivalent plastic, were measured in the neutron beam. An A-150 tissue equivalent plastic to ICRU tissue absorbed dose conversion factor of 0.92 {+-} 0.04 determined. Secondly, variations in the radiobiological effectiveness (RBE) in the beam were mapped by determining variations in two related quantities, e{sup *} and R, with field size and depth in tissue. Maximal variation in e{sup *} and R of 9% and 15% respectively were determined. Lastly, the feasibility of utilizing the boron neutron capture reaction on boron-10 to selectively enhance the tumor dose in the NTF beam was investigated. In the unmodified beam, a negligible enhancement for a 50 ppm boron loading was measured. To boost the boron dose enhancement to 3% it was necessary to change the primary proton energy from 66 MeV and to filter the beam by 90 mm of tungsten.

The response of a given material to an incident electromagnetic wave is described by the energy dependent complex index of refraction n = 1 {minus} {delta} + i{beta}. In the extreme ultraviolet (EUV)/soft x-ray spectral region, the need for accurate determination of n is driven by activity in areas such as synchrotron based research, EUV/x-ray lithography, x-ray astronomy and plasma applications. Knowledge of the refractive index is essential for the design of the optical components of instruments used in experiments and applications. Moreover, measured values of n may be used to evaluate solid state models for the optical behavior of materials. The refractive index n of Si, Mo and Be is investigated in the EUV/soft x-ray region. In the case of Si, angle dependent reflectance measurements are performed in the energy range 50--180 eV. The optical constants {delta}, {beta} are both determined by fitting to the Fresnel equations. The results of this method are compared to the values in the 1993 atomic tables. Photoabsorption measurements for the optical constants of Mo are performed on C/Mo/C foils, in the energy range 60--930 eV. Photoabsorption measurements on Be thin films supported on silicon nitride membranes are performed, and the results are applied …

A mathematical model is created of the dynamic response of pressures caused by flow inputs to an existing distributed helium refrigeration system. The dynamic system studied consists of the suction and discharge pressure headers and compressor portions of the refrigeration system used to cool the superconducting magnets of the Tevatron accelerator at the Fermi National Accelerator Laboratory. The modeling method involves identifying the system from data recorded during a series of controlled tests, with effort made to detect locational differences in pressure response around the four mile accelerator circumference. A review of the fluid mechanics associated with the system indicates linear time invariant models are suitable for the identification, particularly since the governing equations of one dimensional fluid flow are approximated by linear differential equations. An outline of the experimental design and the data acquisition system are given, followed by a detailed description of the modeling, which utilized the Matlab programming language and associated System Identification Toolbox. Two representations of the system are presented. One, a black box model, provides a multi-input, multi-output description assembled from the results of single input step function testing. This description indicates definite variation in pressure response with distance from the flow input location, and …

Multilayer thin films are used as Bragg reflectors for soft x-rays in the energy range 50eV < E < 1000eV in many x-ray optics applications such as x-ray microscopes and telescopes, reducing optics for extreme ultraviolet (EUV) lithography, and x-ray polarizers and phase retarders. Applications often depend critically on reflectivity, which has not been systematically characterized for multilayer periods below 20{angstrom}. For this study, W/B{sub 4}C multilayers were fabricated by magnetron sputtering on Si(111), with periods from 48{angstrom} to as little as 4.7{angstrom}. The x-ray reflectivity measured at {lambda} = 1.54{angstrom} and at 45{degrees} incidence (289 eV < E < 860 eV) was found to decrease sharply for multilayer periods less than 15-20{angstrom}. Examination by high-resolution transmission electron microscopy (HRTEM) showed an expansion of the thickness of the W-rich layers of 30-40% from the nominal values, consistent with intermixture of the two materials during sputter growth, and discontinuous W-rich layers for multilayer periods below about 15{angstrom}. The experimental data for the specular reflectivity in the hard and soft x-ray regimes and the diffuse scattering fit well to a model of multilayer roughness. The model is expressed as a power-law dependence of roughness on spatial frequency. Analysis of small-angle scattering in …

The oxidation behavior of high strength and high toughness SiC, sintered with Al, B, and C (ABC-SiC), was examined. Kinetic data were acquired and the parabolic rate constant for oxidation was determined and compared with literature data on various SiC materials. The role of secondary phases on the oxide morphology was explored. ABC-SiC was compared to commercially available SiC, Hexoloy, and SiC sintered with 10% yttrium aluminum garnet (YAG). Two-step sintering (pre-coarsening) was employed with holds for 48 hours at 600--1,600 C, prior to the typical hot-pressing conditions of 1,900 C for 1 hour, to change the chemistry and reduce the number of bubbles in the silica scale. The effects on the oxide thickness and integrity was examined as a function of the precoarsening heat treatment temperature. Additionally, the hot-pressed ABC-SiC was subjected to heat treatments (anneals) at 1,800 C for 1 hour in nitrogen, Ar, and vacuum environments, and the effects on subsequent oxidation were evaluated. The Ar and vacuum heat treatments dramatically improved the oxidation resistance of ABC-SiC. Finally, reoxidation experiments were performed to try to alter the surface chemistry of the SiC to improve the oxidation resistance. The four-point bend strengths and two-parameter Weibull plots of the …

EUV lithography is a promising and viable candidate for circuit fabrication with 0.1-micron critical dimension and smaller. In order to achieve diffraction-limited performance, all-reflective multilayer-coated lithographic imaging systems operating near 13-nm wavelength and 0.1 NA have system wavefront tolerances of 0.27 nm, or 0.02 waves RMS. Owing to the highly-sensitive resonant reflective properties of multilayer mirrors and extraordinarily tight tolerances set forth for their fabrication, EUV optical systems require at-wavelength EUV interferometry for final alignment and qualification. This dissertation discusses the development and successful implementation of high-accuracy EUV interferometric techniques. Proof-of-principle experiments with a prototype EUV point-diffraction interferometer for the measurement of Fresnel zoneplate lenses first demonstrated sub-wavelength EUV interferometric capability. These experiments spurred the development of the superior phase-shifting point-diffraction interferometer (PS/PDI), which has been implemented for the testing of an all-reflective lithographic-quality EUV optical system. Both systems rely on pinhole diffraction to produce spherical reference wavefronts in a common-path geometry. Extensive experiments demonstrate EUV wavefront-measuring precision beyond 0.02 waves RMS. EUV imaging experiments provide verification of the high-accuracy of the point-diffraction principle, and demonstrate the utility of the measurements in successfully predicting imaging performance. Complementary to the experimental research, several areas of theoretical investigation related to the novel …

This thesis reports on the measurement of the W and Z boson inclusive production cross sections ({sigma}{sub W} and {sigma}{sub Z}) times electronic branching ratios (Br(W {yields} e{nu}) and Br(Z {yields} ee)) in p{anti p} collisions at {radical}s = 1.8 TeV. The analysis is based on 12.8 pb{sup -1} of data taken in the 1992-1993 run by the D0 detector at the Fermilab Tevatron collider; the cross sections were measured to be: {sigma}{sub W} {center_dot} Br(W {yields} e{nu}) = 2. 36 {+-} 0.02 {+-} 0.07 {+-} 0.13 nb and {sigma}{sub Z} {center_dot} Br(Z {yields} ee) = 0.218 {+-} 0.008 {+-} 0.008 {+-} 0.012 nb. The first error is statistical, the second error represents the non- luminosity systematic error, and the third error shows the uncertainty in the luminosity determination. Future prospects for similar measurements based on larger samples of data are discussed.

This dissertation describes the measurement of the top quark mass m{sub t} using events recorded during a 125 pb{sup -1} exposure of the D0 detector to {radical}s=1.8 TeV {anti p}p collisions. Six events consistent with the hypothesis t{anti t} {yields} bW{sup +}, {anti b}W{sup -} {yields} b{anti l}{nu}, {anti b}l{anti {nu}} form the dilepton sample. The kinematics of such events may be reconstructed for any assumed mt, and the likelihood of each such solution evaluated. A measurement of m{sub t} based on these relative solution likelihoods gives m{sub t} = 169.9 {+-} 14.8 (stat.) {+-} 3. 8 (syst.) GeV/c{sup 2}. A 2C kinematic fit is performed on a sample of 77 events consistent with t{anti t} {yields} bW{sup +}, {anti b}W{sup -} {yields} b{anti l}{nu}, {anti b}q{anti q} , and this, in combination with an estimate on the likelihood that each event is top, yields m{sub t} = 173.3 {+-} 5.6 (stat.) {+-} 6.2 (syst.) GeV/c{sup 2} . A combination of these two measurements gives m{sub t} = 173.1 {+-} 5.2 (stat.) {+-} 5.7 (syst.) GeV/c{sup 2}.

A new methodology is proposed for the efficient determination of Green`s functions and eigenstates for quantum systems of two or more dimensions. For a given Hamiltonian, the best possible separable approximation is obtained from the set of all Hilbert space operators. It is shown that this determination itself, as well as the solution of the resultant approximation, are problems of reduced dimensionality for most systems of physical interest. Moreover, the approximate eigenstates constitute the optimal separable basis, in the sense of self-consistent field theory. These distorted waves give rise to a Born series with optimized convergence properties. Analytical results are presented for an application of the method to the two-dimensional shifted harmonic oscillator system. The primary interest however, is quantum reactive scattering in molecular systems. For numerical calculations, the use of distorted waves corresponds to numerical preconditioning. The new methodology therefore gives rise to an optimized preconditioning scheme for the efficient calculation of reactive and inelastic scattering amplitudes, especially at intermediate energies. This scheme is particularly suited to discrete variable representations (DVR`s) and iterative sparse matrix methods commonly employed in such calculations. State to state and cumulative reactive scattering results obtained via the optimized preconditioner are presented for the two-dimensional …

Since the gains associated with solar thermal energy technologies are comparatively small in relation to the required capital investment, it is vital to maximize conversion efficiency. While providing the necessary function of freeze protection, the heat exchanger commonly included in solar domestic water heating systems represents a system inefficiency. This thesis explores two alternate methods of providing freeze protection without resorting to a heat exchanger. Commonly, collectors are made of rigid copper tubes separated by copper or aluminum fins. Cracking damage can occur when water is allowed to freeze and expand inside the non compliant tubes. The possibility of making collectors out of an elastic material was investigated and shown to be effective. Since unlike copper, elastomers typically have low thermal conductivities, the standard collector performance prediction equations do not apply. Modified thermal performance prediction equations were developed which can be used for both low and high thermal conductivity materials to provide accurate predictions within a limited range of plate geometries. An elastomeric collector plate was then designed and shown to have comparable performance to a copper plate collector whose aperture area is approximately 33% smaller. Another options for providing freeze protection to an SDHW system is to turn it …