From NMR Wiki
The R2 relaxation is the reciprocal of the time constant (T2). T2 is the time constant that measures the decay of the transverse relaxation[1, 1, 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]
