Tài liệu Magnetic resonance potx

Applied physics group, Physics department, CBNU Contents: Introduction Theory basis The basis of experiments Summary Next slide Applied physics group, Physics department, CBNU Magnetic resonance is a phenomenon found in magnetic systems that possess both magnetic moments and angular momentum Magnetic resonance is an analytical technique based on a property of matter called spin Magnetic resonance techniques include: Magnetic resonance imaging (MRI), Nuclear magnetic resonance (NMR), Electron spin resonance (ESR), Electron paramagnetic resonance (EPR) Magnetic resonance techniques are generally non-invasive and non-destructive Next slide Applied physics group, Physics department, CBNU Magnetic resonance technique applications MRI is used by clinicians to produce tomographic images of the inside of the human body MRI is also used by scientists to study materials as it is a non-destructive imaging technique NMR is used by scientists to study the structure and dynamics of molecules ESR and EPR are used by scientists to study structure and reactions of free radicals Next slide Applied physics group, Physics department, CBNU Next slide Applied physics group, Physics department, CBNU A system such as a nucleus may consist of many particles coupled together so that in any given state, the nucleus possesses a total magnetic moment µ and a total angular momentum J Two vectors may be taken as parallel µ = γJ where γ is a scalar called the “gyromagnetic ratio” In quantum theory, we have J = I where I stands for a dimensionless angular momentum operator Next slide Applied physics group, Physics department, CBNU  As an external magnetic field is applied, this field produces an interaction energy of nucleus of amount -µ H The Hamiltonian: H = - µH H = -γ  H0Iz in the z-direction, and E = γ  H0m with m = I, I-1, ….-I (2I + values) Next slide Applied physics group, Physics department, CBNU m H0 3   +1 2  -3/2 3   µH  2  -1/2 3  H  µ 0 2  +1/2 +3/2 3  −  µH  2  3  −  µH  2  The energy of the four sublevels of a nucleus with spin I=3/2 when placed in a magnetic field H0  To satisfy the conservation of energy, ω = ∆ E ∀ ∆E is the energy difference between the initial and final nuclear Zeeman energies ∀ ω is an angular frequency Next slide Applied physics group, Physics department, CBNU  For producing magnetic resonance, an alternating magnetic field is applied perpendicularly to the static magnetic field, and is written by H pert= -γ  H0x Ixcosω t Consequently, the allowed transitions are between levels adjacent in energy, giving ω = ∆ E = γ  H0 H x H0 or ω = γ H0  On the other hand, for a particle with mass m and charge e moving in a circular path of radius r with period T J = mvr = m.2π r2/T While the magnetic moment is µ = iA, because i = (e/c)(1/T), we have µ = eπ r2/cT, then deducing γ = e/2mc Next slide Applied physics group, Physics department, CBNU Experiments m =+ A Oven dH dz C dH =0 dz m =− B dH dz Detector m =+ Slit The atomic beam arrangement of I Rabi and collaborators used to detect magnetic resonance transitions in atomic energy levels Next slide Applied physics group, Physics department, CBNU X -in Electromagnet pole faces Magnet Power supply X–Y recorder B Y -in Keithley 610A D Crystal Magic T Cavity and sample A Sync in Microwave Oscillator And power supply C Dummy load Schematic arrangement of apparatus for an electron paramagnetic resonance experiment in the microwave region Next slide Applied physics group, Physics department, CBNU Conclusion With a large masses have low γ’s, a factor of 1000 lower γ for nuclei than for electrons We can change ω by changing Ho, but in most cases it is advantageous to use as large a magnetic field as possible The electronic systems have a resonance in the microwave frequency region The nuclear systems have a resonance in the radio frequency region Next slide Applied physics group, Physics department, CBNU Next slide Applied physics group, Physics department, CBNU Thanks for your attention! The end ... spin Magnetic resonance techniques include: Magnetic resonance imaging (MRI), Nuclear magnetic resonance (NMR), Electron spin resonance (ESR), Electron paramagnetic resonance (EPR) Magnetic resonance. .. group, Physics department, CBNU Magnetic resonance is a phenomenon found in magnetic systems that possess both magnetic moments and angular momentum Magnetic resonance is an analytical technique... physics group, Physics department, CBNU  For producing magnetic resonance, an alternating magnetic field is applied perpendicularly to the static magnetic field, and is written by H pert= -γ  H0x