| Budget Amount *help |
¥7,500,000 (Direct Cost: ¥7,500,000)
Fiscal Year 1991: ¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 1990: ¥4,300,000 (Direct Cost: ¥4,300,000)
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| Research Abstract |
This year, we purchased an instrument for determining grain size distribution. The measurement is based on the scattering of laser light. Accretional growth of fine particles in air was successfully measured with this instrument. This is the first measurement of accretional processes in air on materials which are related to planetary sciences, although there have been some reports on accretion in liquids in the field of colloidal science. The environment in which the measurements were made is quite different from that in the primitive solar nebula. For instance, the number density of fine particles is much larger in the laboratory than that in the primitive solar nebula. Therefore, the information we need is not the growth rate of particles in the laboratory environment, but is the sticking probability of fine particles. We are able to estimate the sticking probability as follows. First we assume that the motion of fine particles in air is mainly due to Brownian motion. From the optica
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l measurement, we are able to estimate the number density of fine particles. Then, we are able to estimate the collision frequency of fine particles theoretically. If the sticking probability is 1, then fine particles grow on each collision. The growth rate of fine particles can be calculated easily in this case. If the sticking probability is Ps, then the growth rate is simply reduced by Ps. On the other hand, we are able to measure the growth rate with the optical measurement. Thus comparing the calculated and measured growth rates, we can determine the sticking probability. So far only a few measurements have been made on limited materials. Our tentative conclusion is that the sticking probability is close to 1. There are many problems to be solved before we confirm this tentative conclusion. The materials of the fine particles, the environment in the sample chamber, etc., have to be changed to see what factors could affect the sticking probability of fine particles. Furthermore, the instrument for the grain size measurement is made for measurements of solid spheres but the aggrerates we measure are porous fractals. Therefore, we need to improve the analytic procedure of the scattered light so that we obtain precise size distributions of fractal particles. Less
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