A Magnetic Czochralski semiconductor wafer having opposing first and second sides arranged distant from one another in a first vertical direction is treated by implanting first particles into the semiconductor wafer via the second side to form crystal defects in the semiconductor wafer. The cavity has a diffusely reflective interior surface and an aperture for allowing emission of combined light. At least one of the plurality of thinning edges is provided with a concave portion that is formed by cutting the thinning edge to be recessed in a semicircular shape toward the rear side in the rotational direction, and a center of the semicircular-shaped concave portion is provided on a line extended from the tip end portion of the thinning edge when viewed from a tip end direction of the body.