[en] The test radiation source casing allows testing the response of at least two detectors of significantly different dimensions. Both detectors can be adjusted to a reproducible, accurately defined position relative to one radiation source. The casing is compact and mechanically integral. The dimensions of the casing can be adapted for various geometrical shapes and dimensions of detectors. Inside, the casing is provided with a movable gate and a pull-rod securing the formation of ports of various dimensions for the insertion of detectors. (J.B.)