Question

1. What is the result when you apply the Fourier transform to a free induction decay signal (time domain signal)? 2. Why is pw90 called the 90° pulse width? Why does the 360° pulse result in no signal? (HINT: Study figures 3 and 5) 3. Describe the following components of an NMR spectrometer and describe why they are necessary: super-cooled magnet, shim coils, and sample probe. (HINT: You can describe each of them from different aspects, e.g. what it is made of, what it is used for, in which part of the whole instrument it is placed, etc.) 4. Which relaxation time can be found using an inversion recovery experiment? Which two pulses are used? Briefly explain the experiment. S. What is an advantage and a disadvantage of short relaxation times? (HINT: Think about practicality and read the required readings)

Answer 1

1.In fourier transformation,free induction decay is the observable NMR signal generated by non equilibrium nuclear spin magnetization processing about the magnetic field. This non equilbrium magnetization can be induced , generally by applying a ulse of resonant rado frequency close to the larmor frequency of the nuclears spnins.

If the magnetization vector has a non zero component in the XY plane , then the processing magnetization will induce a corresponding oscillating voltage in a detection coil surrounding the sample.This time duration signal is typicaly digitised and then Fourier transformed in order to obtain a frequency spectrum of the NMr signal.