Spin Echoes with Four Pulses—An Extension tonPulses

Following Das and Saha's method, the response of a nuclear spin system to four rf pulses has been analyzed by using the classical Bloch equations. The calculations enable one to obtain a recursion formula for the number of echoes to be expected with $n$ pulses. Besides, the calculations also yield several other results important from the experimental view. Thus, they provide a method for obtaining $T_1$, the spin-lattice relaxation time, from primary echo measurements alone, and also give an idea of the order of correction necessary in a measurement of $T_2$, the "spin-spin relaxation time," by observation of primary echoes with successive paired pulses of gradually changing intervals.