A proton polarimeter has been constructed at TRIUMF, with design specifications intended to measure the polarization of protons over an energy range of 100 MeV to 300 MeV. It was built as the principle detector in an experiment to determine three spin-transfer parameters of the fundamental π⃗d → p⃗p reaction. In this thesis, some theoretical and experimental design aspects of the spin-transfer measurement are discussed. The intent of this thesis is to describe an experiment¹ which measures the polarization of protons emitted from the πd→ p⃗p reaction, using an unpolarized target². The sole purpose of this experiment is to demonstrate that our polarimeter and general apparatus are capable of identifying the πd → pp events from a large background presence, and that the systematic errors associated with the polarization extraction have been identified. To this extent, the system is ready to produce the proton polarization required for the spin-transfer measurements. ¹This experiment is identical in all respects to the spin-transfer experiment, except that here, the target is unpolarized. ²The polarization of the protons is well know from the analyzing power, An₀, of the time reversed p⃗p → dπ reaction. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The positive muon is an unstable (Tµ =2.2µsec) particle but one with properties very similar to the proton from a chemical and atomic physics point of view. It has, however, a mass only 1/9 that of the proton, a fact which makes it ideal for studying any mass dependence in chemical and physical phenomena. The µSR and MSR techniques have been utilized to study various relaxation phenomena that occur in the gas phase when the muon or muonium (the muon and electron bound state analogous to the hydrogen atom) interacts with its environment. The fraction of muons that thermalize as muonium has also been measured. It was found that 83% of the muons stopping in n₂ formed muonium, the remainder staying in the charged state. Other gases investigated were H₂ (61 %) , CH₄ (86%), NH3(90%), He(0%), Ne(4%), Ar(74%), Kr(100%) and Xe100%). The amplitude of the signal was found to be strongly pressure dependent and this has been explained in terms of the thermalization time of the muons in these gas targets. Various gas mixtures were also studied where it was found that relaxations of the µSR signal occured as a function of added reagent gas concentration. This phenomena has been attributed to reactions of muon molecular ions with the reagent gas, forming muonium thermally. This represents the first reliable measurements of muon relaxation in the gas phase. Evidence is presented indicating that such reactions occur from the first vibrational state of these muon molecular ions. The systems studied and their room temperature rate constants The spin exchange interactions of muonium with NO and 0₂ were also studied as a function of temperature in the range 295K to 478K. The measured rate constants exhibit a temperature dependence consistent with T ½ and hence a constant spin exchange cross section. The temperature averaged spin exchange cross sections found are: for Mu+O₂, 6~SE=9.0±1x10⁻¹⁶cm² and for Mu+NO, 6se = 1 0 . 5±1 x ⁻¹⁶cm². These values are essentially the same as the cross sections found for hydrogen atom spin exchange with the same molecules, in qualitative agreement with current theoretical predictions. / Science, Faculty of / Chemistry, Department of / Graduate

An orbital dependent local spin density-functional (LSD) scheme with a generated exchange, the LSD GX scheme, has been developed based on the correct normalization conditions of an electron gas. This scheme contains no adjustable parameters; the B$ sb1$, B$ sb2$ and $ alpha sp lim$ are constant for all atoms once the shape of the Fermi hole is chosen. These parameters are rigorously calculated using an unspecified Fermi hole correlation factor and they give an exchange density which reduces exactly to the homogeneous free electron gas one at the high electron density limit. / The LSD GX exchange density is corrected for self-interaction (SI) by splitting the total Fermi hole correlation factor into pure-exchange and self-interaction holes. / These new LSD and SI corrected schemes are compared to each other. They also compare very well theoretically and numerically (total energies and eigenvalues) with other local schemes current in the literature. / New equations for the IP and electronegativities of the atoms in these local schemes are derived which give good results.

No description available.

The high-spin states of the nucleus 64Ge have been investigated using the GASP and the EUROBALL arrays of high-purity germanium detectors. In order to achieve the required experimental sensitivity, special selecting devices were used, namely a highly efficient array of liquid scintillators to detect neutrons and the ISIS Si-ball to detect light charged particles, which has been developed in the present work. A detailed decay scheme for 64Ge has been deduced, assigning spins and parities to the levels through a Directional Correlation from Oriented states analysis, an Angular Distribution analysis and a Polarization Correlation from Oriented states analysis. The character of an intense 1665 keV transition, previously reported as a stretched electric dipole with a small multipole mixing ratio, has been established as an electric dipole with a large multipole mixing ratio. The electric dipole strength has been measured using EUROBALL coupled to an early implementation of the EUCLIDES Si-ball and with the Koln plunger device, allowing an experimental estimate of the isospin mixing probability in 64Ge.

Call number: LD2668 .T4 1985 J665 / Master of Science

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 224-236).

NMR is a powerful analytical spectroscopic tool used to perform detailed studies of structure and dynamics of molecules in solution. However, despite NMR's excellent spectral sensitivity, most NMR methods suffer from low detection sensitivity. This low detection sensitivity results largely from extremely small (Boltzmann) nuclear spin polarization at thermal equilibrium--in even the strongest of magnets. This dissertation focuses on selected research areas that maybe used to combat the limitations presented by NMR and measure weak spectral responses with atomic-scale precision. In particular, these methods involve the use of laser-polarized xenon, liquid crystals, and polarization transfer (cross-polarization) techniques to enhance NMR sensitivity and/or measure weak interactions. The potential use of these tools to study host-guest interactions is of particular interest. In certain systems the sensitivity problem of conventional NMR/MRI can be overcome by applying optical pumping (OP) methods to enhance nuclear spin polarization. For instance, OP of noble gases (such as xenon) is employed to dramatically increase their nuclear spin polarization by transferring angular momentum of laser light to electronic and then nuclear spins. Next, cryptophane complexes are ideal choices for fundamental studies of prototypical host-guest interactions. Of general interest when studying host-guest interactions is how (1) physical confinement at the nanoscale and (2) interactions between guest and host may affect the properties, dynamics, interactions, and/or reactivity of a trapped molecule and the host/guest complex as a whole. As a more specific example, we are interested in probing host-guest dynamic coupling, which refers to the relative motion of the guest within the host, determined by the relative sizes and geometries--as well as the interactions involved. With the development of new NMR methods and techniques, we hope to gain insight into mechanisms that underlie complex formation by probing the structures, dynamics and energetic contributions involved in ligand binding, where molecular contributions such as: orientational and motional freedom of the guest; and structure, dynamics, and ordering of the host can influence the behavior of inclusion complexes.

Nuclear magnetic resonance (NMR) spectroscopy has been extensively used to investigate numerous systems of interest, ranging from collections of molecules to living organisms. However, NMR suffers from one key drawback: an inherent lack of detection sensitivity, as compared to other common forms of spectroscopy. This is due to the minute nuclear magnetic moments and low nuclear spin polarization levels at thermal equilibrium (~10-5 to 10-6), and thus necessitates the use of relatively large sample volumes. One way to overcome this low detection sensitivity is to introduce a species with highly non-equilibrium nuclear spin polarization, such as `hyperpolarized' xenon-129. Hyperpolarized xenon can either be used as its own chemical sensor (due to its exquisitely sensitive chemical shift range), or the non-equilibrium polarization may be transferred from xenon to another molecule of interest (such as a protein or inclusion complex). Hyperpolarized xenon is produced through a process known as spin-exchange optical pumping (SEOP), where the angular momentum from resonant, circularly-polarized light is transferred to the electronic spins of an alkali-metal, and is subsequently transferred to the xenon nuclei through gas-phase collisions. While SEOP has been extensively characterized throughout the years, new experimental techniques and emerging technologies have considerably advanced the field in recent years, and may enable a new understanding of the underlying physics of the system. The first five chapters in this dissertation review background information and the principal motivations for this work. Chapter one reviews the basics of NMR, from the various components of the nuclear spin Hamiltonian and different spin-relaxation pathways to the reasons behind the low polarization of nuclear spins at thermal equilibrium and a few alternative methods to `boost' the NMR signal. Chapter two discusses the fundamental aspects of SEOP, including the electronic spin polarization of the alkali-metal, polarization transfer to the xenon nuclei, and different avenues for the spin polarization to be depleted. The third chapter covers the practical considerations of SEOP from the viewpoint of an experimentalist; namely, the experimental differences when using a variety of alkali metals and noble gases, as well as different SEOP apparatuses and experimental parameters. Chapter four details a variety of different light sources that may be used for SEOP; specifically, the use of laser diode arrays (LDAs) are reviewed, including LDAs that have been frequency-narrowed for more efficient light absorption by the alkali metal. The fifth background chapter covers a variety of magnetic resonance applications of hyperpolarized xenon, including molecular biosensors, specific and non-specific binding with proteins, materials studies, and in vivo applications. The sixth chapter is used as an overview of the dissertation research, which is presented in chapters seven through eleven. Chapter seven details the arrangement of the particular SEOP apparatus used in this research, as well as the experimental protocol for producing hyperpolarized xenon. The eighth chapter accounts the implementation and characterization of the first frequency-narrowed LDA used in this research, as well as an equal comparison to a traditional broadband LDA. Chapter nine introduces the use of in situ low-field NMR polarimetry, which was used to distinguish an anomalous dependence of the optimal OP cell temperature on the in-cell xenon density; the low-field set-up is also used to examine the build-up of nuclear spin polarization in the OP cell as it occurs. The tenth chapter covers the use of high power, frequency-narrowed light sources that are spectrally tunable independent of laser power; this allows for the study of changes to the optimal spectral offset as a function of in-cell xenon density, OP cell temperature, and laser power. Xenon polarization build-up curves are also studied to determine if the spectral offset of the laser affects the nuclear spin polarization dynamics within the OP cell. Finally, chapter eleven accounts the use of high power, broadband LDAs to perform SEOP in which cesium is used as the alkali metal; these results demonstrate (for the first time) that the xenon polarization generated by cesium optical pumping can surpass that of rubidium OP under conditions of high laser flux and elevated in-cell xenon densities.