The present invention is directed to load balancing call signaling channels at the times that they are established, the use of variable frequency keep alive mechanisms depending on the state of the call signaling channel, and the establishment of a call signaling channel when resources are available or otherwise based on need. A command is issued in response to an activation signal from the peripheral circuit. This in turn allows for using a sterilizing gas such as EOG to sterilize the radiation detector except the sound output portion 7, the power supply switch 4, and the power supply portion 3, thereby preventing damage caused by a negative pressure in the sound output portion 7. A plurality of gas outlets are distributed over the inner surface of the gas ring, and are fluidicly coupled with a second channel which is disposed between the outer surface and the inner surface of the gas ring.