DHS 157.03(331g)(c)(c) Risk significant material such as special nuclear material or large quantities of uranium hexafluoride. DHS 157.03(331m)(331m) “Security screening unit” means a non-human use open-beam or cabinet x-ray system with accessible openings designed for the detection of weapons, bombs, or contraband concealed in baggage, mail, packages or other commodities or structure. DHS 157.03(331r)(331r) “Security zone” means any temporary or permanent area established by the licensee for the physical protection of category 1 or category 2 quantities of radioactive material. DHS 157.03(332)(332) “Self-contained breathing apparatus” or “SCBA” means an atmosphere-supplying respirator for which the breathing air source is designed to be carried by the user. DHS 157.03(333)(333) “Shadow tray” means a device attached to the radiation head to support auxiliary beam blocking material. DHS 157.03(334)(334) “Shallow dose equivalent” or “Hs” means the dose equivalent at a tissue depth of 0.007 centimeter (7 mg/cm2). “Shallow dose equivalent” applies to the external exposure of the skin of the whole body or the skin of an extremity. DHS 157.03(335)(335) “SI” means the abbreviation for the International System of Units. DHS 157.03(336)(336) “Shielded position” means the location within the radiographic exposure device, source changer or storage container that, by manufacturer’s design, is the proper location for storage of the sealed source. DHS 157.03(336m)(a)(a) “Shielded room” means a room housing a radiation generating device where, with the device at maximum technique factors, the exterior room environs meets the unrestricted area dose limits of 0.02 mSv (2 mrem) in any one hour and 1 mSv (100 mrem) in a year at 30 cm from the surface of the barrier. DHS 157.03(337)(337) “Shutter” means a device attached to the tube housing assembly which may totally intercept the useful beam and which has a lead equivalency not less than that of the tube housing assembly. DHS 157.03(338)(338) “Sievert” or “Sv” means the SI unit of dose equivalent. The unit of dose equivalent is the joule per kilogram. The special unit of dose equivalent (rem) is being replaced by the sievert. 1 Sv=100 rem. DHS 157.03(339)(339) “Single tomogram system” means a CT x-ray system which obtains x-ray transmission data during a scan to produce a single tomogram. DHS 157.03(340)(340) “Site area emergency” means an event may occur, is in progress, or has occurred that could lead to a significant release of radioactive material and require a response by offsite response organizations to protect people offsite. DHS 157.03(341)(341) “Site boundary” means that line beyond which the land or property is not owned, leased or otherwise controlled by the licensee or registrant. DHS 157.03(342)(342) “Source” means the region and material from which the radiation emanates. DHS 157.03(343)(343) “Source applicator” means a device used to place a radioactive source in a precise anatomical location within the body. DHS 157.03(344)(344) “Source assembly” means an assembly that consists of the sealed source and a connector that attaches the source to the control cable. The source assembly may include a ballstop to secure the source in the shielded position. DHS 157.03(345)(345) “Source changer” means a device designed and used for replacement of sealed sources in radiographic exposure devices and which may also be used for transporting and storing sealed sources. DHS 157.03(346)(346) “Source holder” means a housing or assembly into which a radioactive source is placed to facilitate the handling and use of the source in well logging operations. DHS 157.03(347)(347) “Source-image receptor distance” or “SID” means the distance from the source of radiation to the center of the input surface of the image receptor. DHS 157.03(348)(a)(a) Uranium or thorium, or any combination thereof, in any physical or chemical form. DHS 157.03(348)(b)(b) Ores that contain by weight one-twentieth of one percent or more of uranium, thorium or any combination of uranium and thorium. Source material does not include special nuclear material.