Experimental accessibility of nuclear relaxation parameters

As anticipated in Section 3.2, a nuclear longitudinal relaxation rate R can be defined only when relaxation is an exponential process. This is at variance with nuclear transverse relaxation, which is always exponential and always defined by the transverse relaxation rate / 2- As far as longitudinal relaxation is concerned, when the return to the equilibrium value Mz (oo) of longitudinal nuclear magnetization after a 180° pulse is exponential, we can write (see Section 1.7.4) 

If we consider that relaxation is further enhanced by interaction with a paramagnetic center, Eq. (3.40) becomes 

The meaning of Eq. (3.41) is that any further decay function is multiplied by the original decay function if they are independent (see also Section 3.2). If both 

Experimental techniques are available to measure magnetization recovery under different conditions. These are, for instance, the selective and non-selective variants of the inversion recovery experiment described in Section 1.7.4, and will be discussed in more detail in Chapter 9. We anticipate here, from Chapters 7 and 9, in a qualitative way, the kind of information contained in these experiments. 

---