FIG. 1 is a front view of a radiation measuring apparatus; FIG. 2 is a rear view thereof; FIG. 3 is a top view thereof; FIG. 4 is a bottom view thereof; FIG. 5 is a right side view thereof; FIG. 6 is a left side view thereof; FIG. 7 is a rear, right side perspective view thereof; and, FIG. 8 is a front, right-side perspective view thereof. The broken lines depict environmental subject matter only and form no part of the claimed design.