8. Clouds of charged nuclei

In 1897 Wilson experimented with radiation from radioactive uranium as well as ionisation produced by X-rays. He suggested that the condensation nuclei were free ions produced by the rays, whose charge would encourage the cloud formation.

Wilson tried exposing the air to X-rays for longer, but it didn't reduce the amount of expansion needed to make the clouds appear. He also found that both the radiation from uranium and the ionisation produced by X-rays produced the same sort of condensation.

To prove that the condensation nuclei were charged ions, Wilson put an electric field around the cloud chamber. Even a weak electric field swept the ions away so quickly that no clouds formed.

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