Hyperspectral Imaging for Temperature Measurements of Hot Spots in Shocked Plastic-Bonded Explosives*

Hot spots are formed when energetic microstructures are shocked and they play a critical role in shock sensitivity.  It is important to know both the time-dependent size and temperature of the hot spots in order to generate a kinetic model to describe reaction growth in plastic-bonded explosives (PBX).  Here we use a recently developed technique where PBX is fabricated in the form of a thin wafer, embedded within a polymer binder, and shocked with a laser-launched flyer plate that produces pressures in the 10-40 GPa range.  In this method, every crystal (HMX) can be observed during the shock and hot spots can be seen via their thermal emission, which is detected with 8 nanosecond cameras and a 32-channel optical pyrometer.  With the pyrometer, the spectral radiance of the thermal emission is fit to a graybody model to determine the emissivity and temperature.  The emissivity represents the size of the hot spot, but the pyrometer gives only a spatial average.  In our hyperspectral imaging experiments, we cover half the 8 cameras with a red filter and half with a blue filter.  On any shot we get 4 pairs of time-resolved images which can be analyzed to obtain the spatially resolved (about 2 micron resolution) hot spot temperatures and emissivities.  The validity of the hyperspectral measurements can be confirmed by comparing them to the pyrometer measurements which have a much greater sensitivity and signal to noise ratio.