Showing papers by "Clifford Frondel published in 1955"

The mineral composition of gummite

Abstract: Report discussing the mineral composition and other properties of gummite or "fine-grained yellow to orange-red alteration products of uraninite whose true identity is unknown." Sections include the history and nomenclature of gummite, chemical analyses of gummite, sequential alteration of gummite, and description of minerals in gummite.

A precision x-ray powder camera

Abstract: In the cylindrical camera here described, the sample is successively photographed on the peripheral positions at opposite ends of a diamerer, the film remaining unmoved during the operation. This gives two backreflection photographs that are symmetrically opposed on the same strip of film (Fig. 1). This technique has the fundamental advantage over other back-reflection camera designs in that it permits the effective camera diameter to be computed directly from film measurements. The manner of film mounting is immaterial. The construction of the camera is apparent from Figs. I-4. The r-ray beam is sharply collimated by a long narrow rectangular slit system that is permanently fixed in a diametral position within the body of the camera itself. There is no focussing, as in conventional back-reflection cameras. The powder sample is prepared as a flat disc. The disc is mounted on the end of a tubular, removable, rotating fixture so that its surface is tangent to the (projected) inner surface of the film at the end of the diameter where *-ray beam impinges. The fixture sample is mounted on ball bearings (Fig. 4). The sample in reality is located between the open ends of the film or within a hole punched in the film. The opposite, or inlet, end of the slit system is covered by a removable tubular shield inserted through the inlet port to prevent scattering from the end of the slit system. In practice, the sample is first photographed at one port. The sample-fixture and slit shield are then interchanged (in the dark), the camera rotated 1800 on its axis, and the sample rephotographed. The film, strongly clamped in place by steel rings along its sides, is not moved during the operation. A removable, cylindrical shield of suitable dimension can be mounted around the sample at each port inside the camera for the purpose of shielding ofi reflections below some predetermined angle of d. The shields are not needed if there is no undesirable overlap of lines on the front and back patterns. The method employed for rotating the camera 1800 between the two exposures can be described with reference to Fig. 3. The annular ring A, secured to the camera body by four machine screws within slots, contains two diametrically opposite key holes, D. The camera is lined up for use as follows: axle lock B and the screws holding ring A are loosened and the camera rotated until the x-raybeam passes with maximum intensity