LBNL·48994 ERNEST ORLANDO LAWRENCE BERKELEY NATIONAL LABORATORY Ultra-Low Field Magnetic Resonance Using Optically Pumped Noble Gases and SQUID Detection Annjoe G. Wong-Foy Materials Sciences Division May 2001 Ph.D. Thesis

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Ultra-low field magnetic resonance using optically pumped noble gases and SQUID detection

Observation of Nuclear Quadrupole Resonance with Superconducting Magnetometers.

Conventional pure nuclear quadrupole resonance (NQR) is a technique well suited for the study of very large quadrupolar interactions Numerous nuclear magnetic resonance (NMR) techniques have been developed for the study of smaller quadrupolar interactions However, there are many nuclei which have quadrupolar interactions of intermediate strength Quadrupolar interactions in this region have traditionally been difficult or unfeasible to detect This work describes the development and application of a SQUID NQR technique which is capable of measuring intermediate strength quadrupolar interactions, in the range of a few hundred kilohertz to several megahertz In this technique, a dc SQUID (Superconducting QUantum Interference Device) is used to monitor the longitudinal sample magnetization, as opposed to the transverse magnetization, as a rf field is swept in frequency This allows the detection of low-frequency nuclear quadrupole resonances over a very wide frequency range with high sensitivity The theory of this NQR technique is discussed and a description of the dc SQUID system is given In the following chapters, the spectrometer is discussed along with its application to the study of samples containing half-odd-integer spin quadrupolar nuclei, in particular boron-11 and aluminum-27 The feasibility of applying this NQR technique in the study of samples containingmore » integer spin nuclei is discussed in the last chapter 140 refs, 46 figs, 6 tabs« less

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Low-frequency nuclear quadrupole resonance with a dc SQUID

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) techniques have been very successful in obtaining molecular conformation and dynamics information. Unfortunately, standard NMR and NQR spectrometers are unable to adequately detect resonances below a few megahertz due to the frequency dependent sensitivity of their Faraday coil detectors. For this reason a new spectrometer with a dc SQUID (Superconducting Quantum Interference Device) detector, which has no such frequency dependence, has been developed. Previously, this spectrometer was used to observe {sup 11}B and {sup 27}Al NQR resonances. The scope of this study was increased to include {sup 23}Na, {sup 51}V, and {sup 55}Mn NQR transitions. Also, a technique was presented to observe {sup 14}N NQR resonances through cross relaxation of the nitrogen polarization to adjacent proton spins. When the proton Zeeman splitting matches one nitrogen quadrupoler transition the remaining two {sup 14}N transitions can be detected by sweeping a saturating rf field through resonance. Additionally, simultaneous excitation of two nitrogen resonances provides signal enhancement which helps to connect transitions from the same site. In this way, nitrogen-14 resonances were observed in several amino acids and polypeptides. This spectrometer has also been useful in the direct detection of methyl quantum tunneling splittingsmore » at 4.2 K. Tunneling, frequencies of a homologous series of carboxylic acids were measured and for solids with equivalent crystal structures, an exponential correlation between the tunneling frequency and the enthalpy of fusion is observed. This correlation provides information about the contribution of intermolecular interactions to the energy barrier for methyl rotation.« less

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Bruce Elmer Black

Papers

Methyl Quantum Tunneling and Nitrogen-14 NQR NMR Studies Using a SQUID Magnetic Resonance Spectrometer