What causes the capacitor to leak?
Dry air is a good electrical insulator. A charged air capacitor can store its electrical charge for many hours when there is no load on it. In our circuit, an electrometer connected to the capacitor is used to detect the electrical voltage. Without external influences, this voltage is practically constant.
However, if a particular object is brought into the vicinity of the capacitor (without touching it), the electrical voltage decreases significantly with time. Thus, an electric current flows through the air gap in the capacitor.
Which physical property of our object causes this effect?
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1 solution
Our object consists of a radioactive material that emits alpha, beta or gamma radiation. The collision of these particles or radiation with air molecules breaks up chemical bonds and generates free radicals and ions. These ions are accelerated in the electric field of the capacitor to the oppositely charged electrode, so that an electrical current flows, which slowly discharges the capacitor. This discharge current is a measure of the intensity of the radioactive radiation. Therefore, our circuit is a simple measuring device for the detection of ionizing radiation. The quartz fiber dosimeter also work on this principle.
The ionizing effect of radioactive radiation is particularly dangerous for biological organisms. By radiation, genetic information can be altered, resulting in mutations that can cause cancer. In addition, the nucleotide chains of the DNA can be disrupted so that the cell loses its ability to divide and dies at the end. The total energy of the radioactive radiation need not be particularly large in order to be harmful, because the genetic information is very sensitive. A deadly amount of radiation for humans involves only a few joules per kilogram of body weight. If one senses the heat that emanates directly from the radioactive radiation, then one is probably already dead.