Recently, the depth profile of radicals has become a topic of academic and industrial interest because irradiation with electrons and heavy ions are expected to be used as techniques for improvement of surface properties in polymers and for ultrafine etching in the semiconductor industry. Such high linear energy-transfer radiation produces radicals non-uniformly in a narrow region within several millimeters to a few centimeters of the surface. Adequate knowledge of the distribution of the radicals is also required for radiation health physics.