Radius of Inner circle in the Logo given below is:-

Logo given question is of Radiation Hazard:- Central circles of radius R, an internal radius of 1.5R and an external radius of 5R for the blades, which are separated from each other by 60 degree. Trefoil is black in the international version. Commonly referred to as a Radioactivity warning sign, but it is actually a warning sign of ionizing radiation. Includes X-ray apparatus, medical beam cannons and paicle accelerators.