Gas Density Measurement Using Scattered gamma Radiation

摘要

Collimated gamma rays from a Cs137 source were used as a means of determining the density of air (and other gases confined in an aluminum chamber) by measuring the intensity of the photons scattered by the Compton process at 90 degrees to the direction of the incident beam. The chamber was provided with thin 'windows' of beryllium, so that it was possible to study the effects of chamber wall material and thickness. It was found that (1) the count rate was always proportional to the gas density, (2) the experimental error in the net count rate (the difference between the count rate at one atmosphere pressure and the count rate at near vacuum) was 7.3% for chamber entrance and exit windows of 0.50 inch aluminum, and only 3.3% for windows of 0.25 inch beryllium, (3) the presence of the chamber provided scattering material for gamma photons, producing broad peaks at 370 keV, 182 keV, and 125 keV; using the thicker aluminum windows, the response across the entire energy spectrum was larger than in the case of the thinner beryllium windows, and (4) the presence of the chamber had no effect on the size of the sensitive volume. The technique may be used for measurements associated with jet, ramjet, and rocket engine research.