Radioactivity and its History (Sec 10.1 pg 275-279)

Starting in the late 1800s, there was a lot of scientific study into radioactivity in a short period of time, and it involved the work of many scientists (Fig.1 p.275).

The first major discovery was made in the 1870s using something called a cathode ray tube (old fashioned TVs and computer monitors – see Fig.2 p.276). They found that a beam of particles came off of a negative electrode (cathode) and travelled to a positive electrode (anode). These particles were found to carry a negative charge, and were later were named electrons by J.J. Thompson.

In 1895 Wilhelm Röntgen produced X-rays by bouncing a beam of electrons off a sheet of metal (Fig.4, p.276) – he noticed the emitted rays caused fluorescent minerals to glow, and also exposed photographic film. He named them ‘X-rays’ because he had no idea what they were. He discovered X-rays could penetrate some things like paper and skin, but not materials like metal and bone (Fig.5 p.277).

While Röntgen was experimenting with X-rays Henri Becquerel was experimenting with fluorescent (glowing) materials. He thought they might give off X-rays so he tried exposing them to film, and it worked. He thought the X-rays were absorbed by the rocks from the Sun.

He tried the experiment on a cloudy day and found that it still worked He tried the experiment on a cloudy day and found that it still worked. This meant the rays were being emitted from the rocks themselves. He also noticed these rays were deflected by a magnet, demonstrating they were not X-rays. He named this new ray after himself – for a time they were called ‘Becquerel rays’ CLIP: http://science.howstuffworks.com/29296-100-greatest-discoveries-radioactivity-video.htm

Marie Curie and her husband then experimented with Uranium, polonium, etc and found this radiation was unaffected by temperature, pressure and any other physical factor. They eventually concluded that the radiation came from the core of the atom, and called this spontaneous emission of radiation radioactivity.

Homework time Pg 279 #2, 4, 11