Lawrence Livermore National Laboratory

September 10, 2018

Radiograph sequence of the high explosive Octol during detonation using the new imaging technique. Scale bars are 5 mm.

Many high explosives contain carbon, which condenses during detonation to produce nanometer-scale graphite and diamonds. These forms of carbon and their particle growth reaction rates are neither well known nor easily measured because the optical opacity at the detonation front has, until now, hindered the measurement and study of detonation phenomena at nanoscale time and length scales. The resulting lack of experimental data has been a major roadblock to developing more accurate models for high-explosive detonation. A team of Livermore researchers has recently developed a way to measure carbon condensation using time-dependent, small-angle x-ray scattering.

In a recent Journal of Applied Physics paper, which was selected as an “editor’s pick,” the team describes the development of this imaging capability. It involves placing a material with high x-ray transmission and intense small-angle scattering upstream from the sample in a collimated and focused beam to act as a point-source illumination. With a prudent choice of geometry, this setup, together with a fast detector array at a synchrotron, provides a diagnostic tool that can probe sub-microsecond dynamic phenomena across a centimeter-scale field of view while using a focused, sub-millimeter beam. The researchers note that this imaging method is well-suited for examining the detonation of centimeter-scale explosive charges, as the detonation event can be followed through its entirety.

This effort received Laboratory Directed Research and Development Program funding (14-ERD-018).

[M.H. Nielsen, J.A. Hammons, M. Bagge-Hansen, L.M. Lauderbach, R.L. Hodgin, K.M. Champley, W.L. Shaw, N. Sinclair, J.A. Klug, Y. Li, A. Schuman, A.W. van Buuren, E.B. Watkins, R.L. Gustavsen, R.C. Huber, and T.M. Willey, Single-bunch imaging of detonation fronts using scattered synchrotron radiation, Journal of Applied Physics 123, 225902 (2018), doi: 10.1063/1.5029912.]