A first complication is that the relaxation rate of bulk NaCl solution has a concentration dependence as can be seen in the figure 1.
Figure 1: The longitudinal (1/T1) and transverse (1/T2)
rate of Na in 10 nm pores as a function
of the NaCl concentration (C).
Secondly, it was verified that the ions are in the fast modulation regime and therefore the quadrupolar character of the Na nucleus (I=3/2) can be neglected. Then the pore size dependence was studied, as can be seen in the figure 2.
Figure 2. The measured longitudinal and transverse relaxation
for Na ions as a function of 1/(pore size).
Figure 3 The T2 distributions of H (red line) and Na (black line) in two building materials. The dashed line is the bulk T2 for Na.
L.A.Rijniers, P.C.M.M.Magusin, H.P.Huinink, L.Pel, K.Kopinga, Sodium NMR relaxation in porous materials, Journ. of Magn. Res.167 25-30 (2004)
L.A.Rijniers, J.Petkovic, L.Pel, P.C.M.M.Magusin, K.Kopinga,
of Na and Cl in porous building materials, Mag. Res.
Imaging 21 435 (2003)
L. Rijniers, L.Pel, H.P Huinink, K. Kopinga, Pore size
from hydrogen and sodium NMR using the transverse relaxation at 4.7 T,
Mag. Res. Imaging. 19, 580 (2001)