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High resolution NMR scattering : the first measurement of spin diffusion rates in a homogeneous solid

IP.com Disclosure Number: IPCOM000128036D
Original Publication Date: 1998-Dec-31
Included in the Prior Art Database: 2005-Sep-14
Document File: 5 page(s) / 21K

Publishing Venue

Software Patent Institute

Related People

Zhang, Wurong: AUTHOR [+3]

Related Documents

http://theses.mit.edu:80/Dienst/UI/2.0/Describe/0018.mit.theses/1998-237: URL

Abstract

The first direct measurement of the rate of spin diffusion through a homogeneous sample was performed as an incoherent NMR sca~tering experiment. The experiment consists of a combination of pulsed gradient spin echo methods with multiple pulse / pulsed gradient spatial encoding met-hods. The r+MR scattering experiment involves the creation of an initial spatial magnetization grating, a period of spin evolution including the displacement of spin magnetization, followed by the detection of the residual magnetization grating. The essence of NMR scattering measurements is to record the extent of microscopic motion of spin magnetization through a sample by directly observing amplitude and phase changes of a well defined spin magnetization grating. The spin diffusion measurement records the rate of destruction of a magnetization grating by the random offset of spin magnetization associated with the flip-flop term of the homonuclear dipole-dipole interaction. Since the microscopic motion driven by dipolar coupling is very slow, only fine magnetization gratings are sensitive to the small spatial offsets. Strong pulsed magnetic field gradient techniques were developed for these studies which generate switched gradients with strengths up to 10 3 T/m (a factor of 100 stronger than those commercially available, and a factor of 25 stronger than the highest previously reported). These gradients are able to create a spatial magnetization grating with a pitch of from l m to lnm for solid state NMR scattering experiments. Gradients on the order of 200T/m were applied in the spin diffusion measurement experiment. For single crystal CaF 2 , the measured parallel components of the spin diffusion rates are 7.1 x 10- 12 CM 2 /s along the [0,0,1] direction and 5.3 x 10- 12 cm 2 /s along the [1,1,11 direction, in good agreement with theoretical predictions. Additional work has been done on flow measurement. A noval approach is introduced to measuring flow velocities using a probe with a spatially varying RF field, and without using other magnetic field gradients. The velocities of the spins are measured as a modulation of the NMR signal from the translat,,oil of a spatial magnetization grating through a detection coil with a spatially periodic field profile. Since the same coil can be employed to create the initial magnetization grating, the overall 2 measurement is as simple as recording the signal modulation frequency following a single excitation pulse. The design principles are discussed for a probe that has a spatially periodic field constructed from a series of lumped element 7rcircuits. Spatial modulation of the amplitude or the phase of the RF field can easily be achieved, and either of these may be used to characterize a flow field. Examples are shown of measurements of pipe flow using a probe with an amplitude modulated RF field.

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 This record is the front matter from a document that appears on a server at MIT and is used through permission from MIT. See http://theses.mit.edu:80/Dienst/UI/2.0/Describe/0018.mit.theses/1998-237 for copyright details and for the full document in image form.

High Resolution NMR Scattering: The First Measurement of Spin Diffusion Rates in a Homogeneous Solid

by

Wurong Zhang
B.S., Engineering Physics, Tsinghua University, Beijing, China (1988)

M.S., Engineering Physics, Tsinghua University, Beijing, China (1991) Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Radiological Sciences

at the Massachusetts Institute of Technology

FEBRUARY 1998
SIGNATURE OF author: [[signature omitted]]

Department of Nuclear Engineering

December 22, 1997

CERTIFIED BY: [[SIGNATURE OMITTED]]

David G. Cory Associate Professor of Nuclear Engineering Thesis Supervisor Sow-Hsin Chen

Professor of Nuclear Engineering Thesis Reader

ACCEPTED BY: [[SIGNATURE OMITTED]]

Lawrence M. Lidsky Chairman, Department Committee on Graduate Students ARCHIVES MASSACHUSETTS INSTITUTE OF TECHNOLOGY LIBRARIES AUG 18 1998

Massachusetts Institute of Technology Page 1 Dec 31, 1998

Page 2 of 5

High resolution NMR scattering : the first measurement of spin diffusion rates in a homogeneous solid

High Resolution NMR Scattering: The First Measurement of Spin Diffusion Rates in a Homogeneous Solid

by

Wurong Zhang

Submitted to the Department of Nuclear Engineering on December 22, 1997, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Radiological Sciences

Abstract

The first direct measurement of the rate of spin diffusion through a homogeneous sample was performed as an incoherent NMR sca~tering experiment. The experiment consists of a combination of pulsed gradient spin echo methods with multiple pulse / pulsed gradient spatial encoding met-hods. The r+MR scattering experiment involves the creation of an initial spatial magnetization grating, a period of spin evolution including the displacement of spin magnetization, followed by the detection of the residual magnetization grating. The essence of NMR scattering measurements is to record the extent of microscopic motion of spin magnetization through a sample by directly observing amplitude and phase changes of a well defined spin magnetization grating. The spin diffusion measurement records the rate of destruction of a magnetization grating by the random offset of spin magnetization associated with the flip-flop term of the homonuclear dipole-dipole interaction.

Since the microscopic motion driven by dipolar coupling is very slow, only fine magnetization gratings are sensitive to the small spatial offsets. Strong pulsed magnetic field gradient techniques were developed for these studies which generate switched gradients with strengths up to 103T/m (a factor of 100 stronger than those commercially available, and a factor of 25 stronger than the highest previo...