  We investigate the Rabi oscillations decay of a spin decohered by a spin bath
whose internal dynamics is caused by dipolar coupling between the bath spins.
The decay form and rate as a function of the intra-bath coupling is studied
analytically, and confirmed numerically. The decay in general has neither
exponential/Gaussian or power-law form, and changes non-monotonically with the
intra-bath coupling, decelerating for both slow and fast baths. The form and
rate of Rabi oscillations decay can be used to experimentally determine the
intra-bath coupling strength for a broad class of solid-state systems.
