Ionization Chamber of Victor Hess

This particular chamber was one of seven that were built for Victor Hess at Fordham University ca. 1940. It is constructed of brass and has a four-liter volume.

Measurements were performed using paired chambers. One chamber contained the sample being analyzed and the other compensating chamber contained only nitrogen. The latter chamber was used to account for background. The central electrodes of the two chambers were connected to each other and the fiber of a Lindemann electrometer. The chamber walls (outer electrodes) were given opposite potentials. The wall of the chamber containing the breath sample was given a +135 V potential relative to its central electrode, while the wall of the compensating chamber was given a 135 V potential.

Filling of the chamber was accomplished as follows. The chamber was evacuated and then connected via a drying tube to a spherical glass flask containing the breath sample. This tube contained a desiccant to remove water from the breath sample as it was transferred to the ionization chamber. Another tube from the sample flask was inserted into a jar containing tap water. When the stopcocks were opened, the breath sample was pushed into the evacuated chamber by the water as it replaced the sample in the flask. If the sample was not sufficient to fill the four-liter chamber, aged nitrogen was added until the chamber reached atmospheric pressure.

The diagram below right indicates the electrical circuit of the system.

Three hours were allowed to pass before the measurement was performed to ensure that the radon and its decay products had achieved equilibrium. The actual measurement only took 15 minutes given the sensitivity of the equipment.

Learn more about the electrometer used by Victor Hess.

Reference

Hess, V. F. and McNiff, W.T. Quantitative Determination of the Radium Content of the Human Body and of the Radon Content of Breath Samples for the Prevention and Control of Radium Poisoning in Persons Employed in the Radium Industry Am. J. Roentgenol. And Radium Therapy, 57: 91-102, 1947.