Point density measurement of a gas by coincidence-counting method

The conventional methods used to determine the air stream density, distribution density in shock waves, shock wave thickness, pressure, altitude, etc. are based on the probe-type instruments. Recent developments in the nuclear technology makes it possible to measure properties of a gas without disturbing the media being observed. Coincidence-counting techniques simplify the point density measurement by eliminiting the need to know absolutely the detector efficiences, geometry factors, etc. The background due to cosmic rays, multiple-scattering of photons or particles, wall-scattering, etc. is reduced by this method. Therefore, the source required for this method is smaller than that required by an ordinary nuclear method. A theoretical analysis of this method is discussed. Calculated results for source size for various altitudes are also presented. This study shows that the coincidence-counting method for gas density measurement is good. (author)