What is the radiation-sensitive portion of an ionization chamber composed of?

The radiation-sensitive portion of an ionization chamber is composed of air. This is because an ionization chamber detects radiation by measuring the ionization of the air molecules within the chamber. When ionizing radiation, such as alpha or beta particles, enters the chamber, it interacts with the air and produces ion pairs – negatively charged electrons and positively charged ions. These ion pairs are then collected and measured to determine the intensity of the radiation.

Air is particularly well-suited for this purpose due to its ability to produce a sufficient number of ion pairs with minimal energy loss, allowing for accurate measurements of radiation levels. In contrast, other materials like water, lead, or plastic are not inherently sensitive to ionizing radiation in the same way and would not efficiently facilitate the detection mechanism that relies on the ionization process occurring in air.