7. X-rays produce nuclei

Wilson thought the droplets might be condensing on charged particles, or ions. The droplets could condense on ions just as they did on dust, but ions could exist even in filtered air. To test this idea Wilson tried exposing the air in the cloud chamber to X-rays, which had been discovered in 1895 by the German physicist Wilhelm Röntgen.

The cloud chamber did not produce droplets until an expansion of 1.25, as before, but with X-rays present a huge number of droplets formed, producing a slowly falling fog. Without X-rays this expansion produced only a few hundred droplets per cubic centimetre, a very thin mist.

The presence of X-rays was producing points of nucleation in the chamber. Wilson tried an expansion thirty seconds after the X-rays were turned off, but got the same results as if he never used X-rays at all. Wilson concluded that the X-rays were producing a larger number of the nuclei which naturally occured in air, and that the nuclei dispersed rapidly.

Next Page