Experiments that yield inversion of the Co59thin film nuclear system were carried out. For nanosecond magnetization reversal by a field with a growth rate greater than Oe/s, 85% inversion was obtained. The investigation of the inverted state at frequencies corresponding to hexagonal (α) and f.c.c. (β) phases revealed that Co59-β switches 1.3 times faster than Co59-α. This is explained by the large contribution of rotational processes for Co59in β phase. Longitudinal relaxation time T1is measured by the method of pulse inversion.