What frequency of electromagnetic radiation is needed to excite a nuclear spin flip? Where is radiofrequency (RF) radiation on the energy scale of the electromagnetic spectrum? Is the thermal energy at room temperature large or small compared to the energy of a \(\pi\)-\(\pi\)* transition and to the energy of a nuclear spin flip?What are the consequences of your answers to these questions? If thermal energy has sufficient energy to excite nuclear spin flips, why are there still more in the ground than excited state? Can you think of two processes by which a specific excited state nucleus can get rid of its excess energy? Do excited state nuclei have short or long relaxation times? When the populations of the two levels are equal, can we continue to excite ground state nuclei up to the excited state such that the population of the excited state becomes larger than the population of the ground state, creating what is known as a population inversion? What happens to the population distribution as the energy gap between the ground and excited state is increased? Consider a sample in an NMR tube.The crosshatched region in the tube is the area over which signal is recorded.Why is it important that B APPL be homogeneous over this entire region?