Investigations of the Light Emission during Hypervelocity Particle Impacts

The light emission during impacts of micron-sized particles with speeds between 500 m/sec and 100 km/sec was analyzed. The intensity of the light emission is proportional to the mass of the impacting particles for micron-sized particles with constant speed. Measurements with a light gas gun using millimeter-sized particles showed that this relationship is true for a mass range from 10 exp(-11) to 10 exp(-1) grams. The dependence of the light emission on the particle speed is complicated and depends on the particle and target materials. The spectral distribution of the light emission indicates temperatures of the radiating material of 2000 K - 4000 K. Measurements of the secondary particles created during the impact of a 5 km/sec primary particle showed that the majority of secondary particles is ejected at around 60 degrees from the horizontal at about 1 km/sec. A small fraction is ejected at small angles (around 10 degrees) at speeds of up to 40 km/sec. Theoretical calculations explain the dependence of the light emission on the primary particle velocity by taking melting and vaporization into account. The dependence of the light emission on the ambient pressure in the experiment chamber yielded estimates of how much material vaporized during these impacts.