A hydrogen sample is at equilibrium in a 1.5 Tesla magnetic field. A constant B1 field of 1.17x10-4 Tesla is applied along the +x'-axis for 50 microseconds. What is the direction of the net magnetization vector after the B1 field is turned off?

B1 = 1.17x10-4 T,
τ = 50x10-6 s, and

B1 is applied along the +x' axis.

The relationship between the rotation angle in radians (θ) and the length, in seconds, that the B1 field is applied (τ) is:

θ = 2π τ B1 γ

where: γ = gymagnetic ratio for the nuclei in question.

θ = 2π τ B1 γ

θ = 2π * 50x10-6s * 1.17x10-4T * 42.58 MHz/T

θ = 1.565 rad.

θ = 1.565 rad. * 180o/π rad = 89.673o

The net magnetization vector will be almost along the +y' axis: 89.673o from the +z axis after the clockwise about the +x' axis.