  In this Letter, we consider the role played by the sedimentation of helium
nuclei on the emissivity and metallicity distribution of the X-ray emitting
plasma in the cores of relaxed galaxy clusters. We model the gas density and
temperature profiles of nearby cooling core clusters to estimate the
gravitational acceleration acting on the helium and show that its sedimentation
time scale is too long with respect to the present age of these objects to play
a significant role. However, we argue that these time scales have to be
definitely lower in the past allowing the helium to settle in the cluster
cooling cores and raise its abundance to values higher than the solar one. A
direct consequence of this speculation is that the helium, by increasing the
total X-ray emissivity, reduces the measured metal abundance in the inner (r <
20 kpc) cluster regions.
