The Curie Method Educational content

The ionization chamber

In 1903, Marie Curie wrote that uranium rays “become weak conductors of electricity when they pass through gases”.1

Ionization chamber displayed at the Curie Museum in a showcase devoted to radioactivity measurement.
The cover has been removed to reveal the chamber’s interior and a piece of radioactive ore has been placed between the two plates.
Source: Curie Museum / Uriel Chantraine.

The electrons and ions released as the rays pass through do indeed have an electric charge. The more intense the ionizing radiation, the greater the electric charge that is released. By measuring the electric charge, you can estimate the intensity of the radiation emitted by a radioactive source.

Description of ionization chambers by instrument manufacturer Charles Beaudouin, c. 1930.
Source: Curie Museum archives.

In the Curies’ experiments, the ionization chamber was the instrument that transformed uranium rays into an electric charge. It is composed of two metal plates between which the radioactive substance to be studied is placed.

Each plate is connected to the terminals of a battery or a power generator. The chamber is sealed with a cover that prevents the gas and electric charges from escaping. The radiation released by the substance being studied ionizes the gas inside the chamber, producing positive electric charges (ions) and negative electric charges (electrons).

These electric charges are attracted, respectively, to the negatively and positively charged plates. As they move, the electric charges create an electric current proportional to the radiation. In this way, the ionization chamber acts as a “converter” that transforms radioactivity into electricity. By measuring the electric charge generated by an ore, you can deduce its radioactive emission.


1From Marie Curie’s dissertation, Recherches sur les substances radioactives (Research on Radioactive Substances), 1903.

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