Measuring radon by collecting its progeny is an old technique

It would be nice if a student reproduced the basic technique used by Marie Curie for measuring radioactivity, including the radioactivity of radon progeny. She used a quadrant electrometer to measure collected charge from natural radioactivity on a flat plate which was biased positive or negative and was one side of an open air capacitor. The other side of the capacitor is electrically isolated and connected electrically to one side of a quadrant electrometer. The same side of the electrometer is connected to one electrode on one side of a piezo electric crystal (probably quartz). A piezo electric potential can be produced by placing small weights on a pan attached to the end of the crystal. The position of the mirror attached to the supporting fiber of the quadrant electroscope to view any change in potential of the capacitor plate that collects the air ions produced by the radioactivity on the lower plate. The initial position of the electroscope is viewed by a small telescope to read the reflection of a scale some distance from the mirror. That is, the initial position of the electrometer fiber can be shown with great sensitivity by viewing the scale with the telescope. As the collector plate collects air ions, the potential of the plate causes the electrometer fiber to move. At a suitable elapsed time, weights are added to the pan to produce a piezo potential that cancels the potential collected by the air ions. The weight needed to balance the collected ion charge is a measure of the charge and thus of the radioactivity.

To measure radon progeny, a long wire was biased negative to attract positive recoil atoms which lose electrons after it ejects an alpha particle. After some period of time the wire is disconnected from its voltage source an coiled up to fit on the bottom plate of the "ion chamber". By this means the early workers found that there was more emanation (radon) near water falls. There is also more radon over a freshly plowed field. I wonder if the EPA knows about this.

I hope to place this description with an appropriate diagram on the Virtual Radiation Museum (VRM) which is under construction at http://www.medphysics.wisc.edu/~vrm Your help and suggestions are solicited to have the VRM help educate the public and the radiation professionals about ionizing radiation. Best wishes,