A gas turbine includes a rotor concentrically surrounded by a casing, with an annular hot gas channel axially extending between the rotor and the casing. The rotor includes a plurality of blades arranged annularly on the rotor. Each of the blades is mounted with a root in a respective axial slot on a rim of the rotor radially extending with an airfoil into the hot gas channel and adjoining with an axially oriented root surface to an annular rim cavity. A cooling device is provided at the root of each blade to receive cooling air injected into the rim cavity through stationary injectors. An optimized cooling is achieved by providing an essentially plane root surface and the cooling device includes a scoop for capturing and redirecting at least part of the injected cooling air, which scoop is a recess with respect to the root surface.