Large diameter crystals

Scintillators like NaI(Tl) can be made position-sensitive for applications like 2D-ACAR (section 7) and medical imaging [19]. Light from a large-diameter crystal is detected by a close-packed array of PM tubes. 

It was clearly observed that the phenomenon of delayed crystallization was directly related to the size of the dispersed droplets [Koutsky et al., 1967]. Only the smallest droplets showed crystallization at much larger undercooling droplets having a sufficiently large diameter crystallized at temperatures approaching the bulk crystallization... 

The next step is the hydrogen reduction of the trichlorosilane (Reaction 2 above). The end product is a poly crystalline silicon rod up to 200 mm in diameter and several meters in length. The resulting EGS material is extremely pure with less than 2 ppm of carbon and only a few ppb of boron and residual donors. The Czochralski pulling technique is used to prepare large single crystals of silicon, which are subsequently sliced into wafers for use in electronic devices.1 1... 

Large single crystals of (e.g., 2 X 10 m long and 5 X m in diameter) have been obtained in this type of apparatus - . 

Quenching the vapour with cold air in the chamber may increase the rate of heat removal although excessive nucleation is likely and the product crystals will be very small. Condenser walls may be kept free of solid by using internal scrapers, brushes, and other devices, and all vapour lines in sublimation units should be of large diameter, be adequately insulated, and if necessary, be provided with supplementary heating to minimise blockage due to the buildup of sublimate. One of the main hazards of air-entrainment sublimation is the risk of explosion since many solids that are considered safe in their normal state can form explosive mixtures with air. All electrical equipment should therefore be flame-proof, and all parts of the plant should be efficiently earthed to avoid build-up of static electricity. 

For PETN compacts of about 90% of crystal density, the 50% threshold for shock initiation is about 9 kbar. This threshold is very nearly the same for large diameter plane-wave tests (Ref 18) and for small diameter, divergent wave gap tests (Ref 17).. From the Hugoniot data in Ref 17, the particle velocity, Up, corresponding... 

The gas inlet tube should be of moderately large diameter to prevent becoming plugged with crystals during the saturation with hydrogen sulfide. 

Lead azide crystals should be spherical in shape, opaque in appearance and less than 0.07 mm in diameter. Dextrin is added as a colloiding agent, which prevents the formation of large, sensitive crystals of lead azide and regulates, to some extent, the shape of the crystals. 

The most detailed studies of the shock initiation of Tetryl are those of Iindstrom (Ref 40) and those made at NOL (Refs 30, 32,41 42). Iindstrom used large diameter, unconfined charges and plane-wave shocks. Threshold pressures and particle velocities to just initiate detonation (computed by the writer from Lind-Strom s data in Ref 42a) are shown in Table 4 Note that threshold pressures decrease rapidly as packing d decreases, but particle velocities stay essentially constant (with the possible exception of Tetryl at 1.7g/cc, which is 98% crystal d)... 

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