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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.
A method for direct density measurement of a gas without the use of material probes is proposed and the experimental investigation summarized. The operation of the gas density measuring instrument is based upon the interaction between a gamma-ray beam and the electrons in the gas as described by the Compton scattering principle. Experimental results indicate the practicability of this instrument for use in low density, high temperature wind tunnels and other high temperature gas flows such as rocket exhausts. (Author).
It is theoretically possible to infer the density of a gas from the rate at which particles are scattered out of a beam of subatomic particles which is passed through the gas. This technique offers the possibility of a probeless density measurement which is independent of the state of the gas. Previous research verified that this technique could be implemented using a gamma ray beam, but that the best spatial resolution and measuring time which could be achieved were inadequate to allow the technique to be applied to a low density test facility. In the research reported, the technique was applied using a 50,000-v electron beam. It was found that excellent spatial resolution and measuring time could be achieved at densities as low as 6 x 10 to the -8th power gm/cc. Density profiles were measured in a low density wind tunnel with a nozzle exit diameter of 18 in. and an open jet test section. A spatial resolution of about 1 cm was achieved, and measurements required 10 sec per point. This measuring time can probably be reduced by several orders of magnitude if necessary. The densities measured were repeatable within 1 percent. Accuracy, spatial resolution, and measuring time are found to be interrelated. The constraint on the combination is discussed in detail. The design of equipment is discussed. (Author).