A Classical Perspective Applied field B A"classical"view will help us Precessional orbit understand the measurement process. Magnetic dipole Consider a spinning charged particle in a magnetic field: .Particle will precess at a characteristic frequency Spinning (Larmor Frequency)Vo particle v。=yB./2π (where y=magnetogyric ratio)
射频振荡线圈与外磁 场方向垂直
射频振荡线圈与外磁 场方向垂直
(a) N nucer Excited stale N FIGURE 11.1 Hnuclear Ground statr The spectroscopic transition for nuclear magnetic resonance. Energy is needed to reorient the nuclear magnets in a magnetic field.The energy is absorbed and reemitted at the frequency charac- teristic of the nucleus in its local environment.(a)The large arrow ( represents the external magnetic Excited state field.The two smaller arrows repre. sent the dipole of a nucleus with a nuclear spin /(b)An energy No level diagram for the system in (a). magnetic The splitting is proportional to the field Ground state field. Field on
能童稍高 1 一 N N $外进场 s Ni m✉+ 能址稍低
Instrumental Continuous Wave (CW)NMR original instruments used: Electromagnets (14-23 kG:60-100 MHz) Fixed frequency RF source Swept(variable)magnetic field -measure absorption of applied RF not very sensitive.Why? 2