Scattering Experiment

Henri Becquerel
Discovered radioactivity in 1896

Ernest Rutherford
identified the different forms of radioactivity

2. Radioactivity

At the end of 1895, Wilhelm Röntgen discovered X-rays. He published his results before the end of the year, and word of his discovery spread quickly.

Henri Becquerel heard about the discovery a few months later, when Henri Poincaré described the discovery at a meeting of the French Academy of Science. Röntgen's X-rays had come from the fluorescent glass walls of a cathode ray tube, and Becquerel wanted to see if other luminescent objects could produce the rays.

Becquerel experimented with uranium in February 1896. He exposed the mineral to sunlight to make it luminesce, then laid it on top of a photographic plate wrapped in black paper.

The discovery of radioactivity came on Sunday 1st March 1896. Becquerel had set up the experiment the previous Friday, but it had been cloudy so the uranium could not be made luminescent. He had put the uranium and the plates in a drawer for the weekend, but decided to develop the plates anyway. He found the same fogged images. The uranium salts were radiating even without 'activation' by sunlight.

The phenomenon was named 'radioactivity' by Pierre and Marie Curie at the start of the 20th Century. They had begun studying the phenomenon in 1898 and found that thorium, polonium and radium also showed the same effect. In 1903 the Curies shared the Nobel Prize with Becquerel for their work.

At the same time Rutherford was investigating radioactivity. In 1898 Rutherford confirmed Becquerel's observation that there were at least two parts to the uranium rays. Rutherford named the easily absorbed rays 'alpha' and the more penetrating rays 'beta'. He went on to discover that these rays were particles.

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