Abstract: A method determining the plutonium content of a material containing fluorine involves obtaining the mass ratio of plutonium in a compound comprising plutonium and fluorine, particularly plutonium tetrafluoride, to the total plutonium content. The method utilises a high resolution gamma ray spectrometry technique to obtain a count rate in a pair of gamma ray photopeaks. One of the photopeaks has an energy level of 414 keV, resulting from the decay of plutonium-239, and the other photopeak has an energy level of 583 keV, resulting from the decay of an excited sodium-22 nucleus following an (alpha,n) interaction with fluorine.

Abstract: A closure arrangement comprises an aperture-defining frame, a closure panel member which fits removeably into the frame, and a radio-frequency seal between the frame and an edge of the panel member. The seal is divided into two complementary parts attached respectively to the panel member and to the frame, the parts extending over different sections of the periphery of the aperture and cooperating to cover the entire periphery only when the panel member is closed. To improve the seal, a sharp ridge is formed in the edge of the panel member to enhance the contact pressure exerted on the seal locally on a line extending along the seal.

Abstract: An ice breaker arrangement of forcing open the door of an enclosure such as a radio frequency shelter for electrical equipment comprises a threaded stud (3) which, when turned by a key, is made to project from the door frame (5) so as to force a reaction plate (2) attached to the door (1) away from the frame, thus opening the door (1). Appropriate apertures (21, 73) are provided at each end of the stud (3) to allow access to the stud (3) by the key.