Helmet but it doesnt have any use in FOnline cause the Cathedral is blown up.
FOnline wiki:
It is placed on the head of a psyker to disable or prevent him or her from using his or her powers. A psychic nullifier also blocks incoming telepathic attacks when worn by a non-psyker, such as those frequently experienced in the Corridor of Revulsion. The Vault Dweller can obtain one to aid in passing through the Corridor of Revulsion on the way to the Master.