The ornamental design for an exteriorcase for gammadetector, as shown and described.
FIG. 1 is a perspective view of an exterior case for gamma detector, showing the new design.
FIG. 2 is a front-side view thereof.
FIG. 3 is a rear-side view thereof.
FIG. 4 is a left-side view thereof.
FIG. 5 is a right-side view thereof.
FIG. 6 is a top-side view thereof; and,
FIG. 7 is a bottom-side view thereof.
The broken line showing of non-claimed structural features is included for the purpose of illustrating unclaimed subject matter and forms no part of the claimed design.