P6.2 Radioactivity

P2.6.1 - Observing Nuclear Radiation

• Discovered by accident by Henri Becquerel. 
• - an image of a key appeared on a photographic film when the key was left between the film and a packet of uranium salts.
• - he concluded that something must have passed from the uranium salts through the paper that the film was wrapped in, but it must have been blocked by the metal keys.
• - He asked his assistant, Marie Curie, to have a look into this and she concluded that it was Radioactivity.

How it works

• Radioactive emissions happen when some nuclei of an element are unstable. 
• - they become stable by emitting radiation.
• - there are three types; alpha, beta and gamma
• - alpha and beta are particles whilst gamma is a form of energy.

Background Radiation

• It is everywhere most of the time,
• Most comes from natural resources including;
• - radon gas in the air (50%)
• - radioactive rocks in the ground (14%)
• - cosmic rays (10 %)
• - 12% is in our food
• Only around 13% comes from man made resources mostly medical - using x-rays.
• Less than 1% comes from nuclear power and fallout from nuclear explosions and accidents.

P2.6.2 - The Discovery of the Nucleus

Democtritus (450BC)

• Blind guesses
• Cut stuff in half and thought that repeated cutting into something would get to the part where it could not be split anymore.
• said that everything would be made of particles
• came up with the idea that matter was made of particles.
• called them A Tomos - iron=iron particles
• Each particle was different (cheese=cheese particles)
• - atoms had the particles of the things that they formed.

Dalton (1803)

• Determined that elements existed of discrete particles of matter.
• - thought they were solid spheres of matter that should not be split.
• Reintroduced the ideas that everything was made of atoms 
• - each atom same but had a different arrangement 
• - each element contained identical atoms
• - said that each atom was microscophic and that it couldn't be seen with the eye.

JJ Thomson (1897)

• Made the plum pudding model
• - thought all was negative with positive parts in the middle (floating at random)
• - discovered tiny particles with a negative charge -> these negative particles were given out by atoms and smaller by atoms.
• Managed to estimate the mass of cathode rays 
• - was 1000 times lighter than hydrogen
• - called electrons, corpuses and that they were made of very small light particles -> DISCOVERED THE ELECTRON
• His ideas didn't fit with Dalton's model of the atom, proposed a new model (plum pudding)

Rutherfold + Geiger + Marsden (1907)

• Experiment with a thin sheet of gold foil
• - figured out protons.
• Discovered the nucleus 
• - discovered that most of the atom is empty space.
• Disaproved…