Dynamic measurement of temperature in detonating PBX 9502 using neutron resonance spectroscopy

摘要

Accurate temperature measurements in dynamic systems have been pursued for decades and have usually relied on optical techniques. These approaches are generally hampered by insufficient information regarding the emissivity of the system under study, particularly when looking at detonating energetic materials. This results from the complex chemical change that the detonating system is undergoing, from neat organic crystals with discrete set of electronic states and molecular vibrations embedded in a binder, to gas phase products, with a different set of discrete states. Typically, when making an optical measurement, one makes the grey body approximation and measures the photon flux at a few discrete bands to extract a temperature from the light emission. We are developing NRS techniques to measure temperature in dynamic systems and overcome the limitations of optical systems. Many elements have neutron resonances with narrow enough intrinsic Breit-Wigner (Lorentzian) widths such that the resonance is substantially broadened by atomic motion even at room temperature. Thus, accurate measurement of the Doppler contribution allows one to infer the material temperature, and for the conditions achieved using standard high explosives, the probe itself is not perturbed by the high temperature and pressure. Moreover, since the opacity of energetic materials to neutrons is much less than it is to infrared, visible, or ultraviolet light, we probe the internal temperature, in contrast to measuring the surface temperature through a laser or an emission technique. Also, NRS is much less affected by the opacity of soot or other particulate than are optical methods.