Requirements to get a resonance
The excitation of the nucleus is generated by a high frequency impulsion B1 at a highpower(50 watts) for a short time (10 to 50
).The field B0 is high and constant, the field B1 is assumed to be weak, perpendicular to B0 and rotates in the plane XOY with an angular speed
and in the same sense than
.
Practically (Fig. 4) A small coil put perpendicular in thefield B0 is run by a current. This one causes an osallatory induction along the axis of the coil. We may represent this induction Bx with two magnetic vectors rotating in opposite sens B(l) and B(r), one of which has the same rotation sense than the precession.
The second vector is practically without any influence on the phenomenon.
The emitter coil on the x axis generates a weak electromagietic field B1 linearly polarized with a frequency
and with an amplitude 2B1
