An apparatus and method for supporting plural radioactive sources in operative gauging relationship at different elevations in a vessel containing material and density and/or level of which is to be monitored, and for transporting the radioactive sources to a radiation-proof source holder for storage exteriorly of the vessel when the vessel is being cleaned or the like.In one embodiment the sources are independently supported on a continuous basis on separate cables and transported between the vessel and the source holder by separate winches associated with the source holder, with each winch independently controlling the transport of its respectively associated source. In a second preferred embodiment, also equipped with two winches and capable of separately suspending plural sources in juxtaposition in the source holder, one of the winches is used to transport a first source from the source holder to an intermediate position in the vessel whereupon its support cable is disconnected from the winch and connected to the lower end of a second cable supporting the other source or sources. The second cable is controlled by the second winch to facilitate simultaneous lowering of the entire assembly of interconnected sources at their proper final locations in the vessel. By reversing the foregoing procedure the winches can be used to transport the sources to the storage holder where they are stored in side-by-side position once again suspended from separate cables.In both embodiments of the invention, by reason of storage of plural sources on separate cables in side-by-side position in the storage holder, the height of the storage holder is reduced to approximately one-half of the normal requirement.