  Measurements of the magnetic penetration depth (lambda) in the Fe-based
superconductor Ba_(1-x)Rb_xFe_2As_2 (x=0.3, 0.35, 0.4) were carried out using
the muon-spin rotation muSR technique. The temperature dependence of lambda is
well described by a two-gap s+s-wave scenario with a small gap Delta_1 = 1 - 3
mev and a large gap Delta_2 = 7 - 9 mev. By combining the present data with
those obtained for RbFe_2As_2 a decrease of the BCS ratio 2Delta_2/(k_B)(T_c)
with increasing Rb content x is observed. On the other hand, the BCS ratio
2Delta_1/(k_B)(T_c) is almost independent of x. In addition, the contribution
of Delta_1 to the superfluid density is found to increase with x. These results
are discussed in the light of the suppression of interband processes upon hole
doping.
