PHYS1008 Study Guide - Final Guide: Gyroscope, Rotating Magnetic Field, Transverse Plane
2 Aug 2018
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Document Summary
Whilst precession is the rotation of an induvidual proton, resonance is when they all move together. In the presence of b0 only, the spins precess around b0, but the net magnetisation (m) does not precess. The net magnetisation vector, is the 10/1 million spins which line up with the b0 field. They do not flip up, they align with the field to be in the easiest energy state for them. When the net magnetisation vector is in line with the b0 field they cannot be read. A second magnetic field needs to be applied in a different direction in order to see their movement. B1 = second field added, at the larmor frequency, this causes m to resonate and allows it to be measured. A weak field is applied that rotates around b0. There is net magnetisation of the spins in the presence of b0, the angular momentums of m is aligned but there is no precession.
