MICROPROJECTILE VELOCITIES IN A GAS DRIVEN LAUNCHER

Microprojectile methods of genetic engineering sometimes employ a macr oprojectile which launches the microprojectiles when it hits a stoppin g plate. A study has been made of the relationship between the velocit ies of the macroprojectile and the microprojectile it launches. Macrop rojectile velocities were measured using a beam blanking method and th e microprojectile velocities were measured with a laser Doppler anemom eter. Particles of tungsten, titanium dioxide and silicon carbide were investigated as microprojectiles. The microprojectile velocity was fo und to depend not only on the macroprojectile velocity but also on the microprojectile size and material, the bond strength with the macropr ojectile and the gas flow that develops ahead of the macroprojectile. On average the microprojectile launch velocity was similar to the macr oprojectile velocity. However, some tungsten particles had velocities twice this value. Experimental evidence suggests that these higher vel ocities were caused by early break-way of particles from the macroproj ectile followed by further acceleration by aerodynamic drag arising fr om the gas flow ahead of the macroprojectile.