Nicholas Sinclair

Time resolved small angle X-ray scattering experiments performed on detonating explosives at the advanced photon source: Calculation of the time and distance between the detonation front and the x-ray beam

Time resolved Small Angle X-ray Scattering (SAXS) experiments on detonating explosives have been conducted at Argonne National Laboratorys Advanced Photon Source Dynamic Compression Sector. The purpose of the experiments is to measure the SAXS patterns at tens of ns to a few μs behind the detonation front. Corresponding positions behind the detonation front are of order 0.1–10 mm. From the scattering patterns, properties of the explosive products relative to the time behind the detonation front can be inferred. This report describes how the time and distance from the x-ray probe location to the detonation front is calculated, as well as the uncertainties and sources of uncertainty associated with the calculated times and distances.

Single-bunch imaging of detonation fronts using scattered synchrotron radiation

A centimeter-scale field of view for transmission X-ray radiography from a sub-millimeter-focused synchrotron X-ray beam is achieved by placing a strongly scattering material upstream of the sample. Combining the scattered beam with a detector system synchronized and gated to acquire images from single X-ray pulses provides the capability for time-resolved observations of transient phenomena in samples larger than the native X-ray beam. Furthermore, switching between this scatter-beam imaging (SBI) and scattering modes is trivial compared to switching between unfocused white beam imaging and scattering using a focused pink beam. As a result, SBI additionally provides a straightforward method to precisely align samples relative to the focused X-ray beam for subsequent small-angle X-ray scattering measurements. This paper describes the use of glassy carbon for SBI to observe phenomena during detonation of small-scale high explosive charges and compares the technique to conventional white beam imaging. SBI i...

In Situ Observations of Phase Changes in Shock Compressed Forsterite

Shockwave data on mineral‐forming compounds such as Mg2SiO4 are essential for understanding the interiors of Earth and other planets, but correct interpretation of these data depend on knowing the phase assemblage being probed at high pressure. Hence direct observations of the phase or phases making up the measured states along the forsterite Hugoniot are essential to assess whether kinetic factors inhibit the achievement of the expected equilibrium, phase‐separated assemblage. Previous shock recovery experiments on forsterite, which has orthorhombic space group Pbnm, show discrepant results as to whether forsterite undergoes segregation into its equilibrium phase assemblage of compositionally distinct structures upon shock compression. Here, we present the results of plate impact experiments on polycrystalline forsterite conducted at the Dynamic Compression Sector of the Advanced Photon Source. In situ x‐ray diffraction measurements were used to probe the crystal structure(s) in the shock state and to investigate potential decomposition into periclase and bridgmanite. In contrast to previous interpretations of the forsterite shock Hugoniot, we find that forsterite does not decompose, but instead reaches the forsterite III structure, which is a metastable structure of Mg_2SiO_4 with orthorhombic space group Cmc2_1.