|
Flash radiographs have long been useful for interpreting dynamic events. Such interpretation ranges from merely looking at a radiograph to aid in understanding the event to fully deconvolving film densities to reconstruct actual masses and positions. Between these two extremes are the possibilities of using trained observers to select features of interest or of using densitometers to aid in such descriptions. Several examples of these latter methods will be illustrated to indicate that reasonable precision can be obtained in this way and that flash radiography can indeed.be a quantitative science. The examples will be from the field of shock-wave hydrodynamics.1 The radiographs were taken at the PHERMEX facility,2 a 25-MeV machine emitting about 30 R at a meter in a pulse of 100 ns for these examples. The first situation involves the selection of the position of a thin, low-density beryllium foil embedded in a moving high-density material, uranium. The second will involve the selection of the location or of the alignment direction of step mass discontinuities such as those found in shock waves or in interfaces between materials of different density. Such discontinuities may be slowly curving, and the problem is that of determining tangents at selected locations. Both spall in lead and multiple intersecting shocks in lead will be described. The third situation will involve the selection of the alignment of the head of a rarefaction wave--the problem of a density gradient with a discontinuous first derivative. The example will be oblique reflection of a detonation wave from an open edge in the explosive PBX-9404. The last situation will involve the problem of a material density gradient with continuous first derivative. The example will be low-density material ejected from a lead surface that has been shocked. In this last case the answer is not a single selection, but a variation as a function of location.
|
