Radiation

Menu The Atom History of the Atom Alpha Scattering Mass & Atomic Numbers Isotopes Fission Nuclear Equations

The ATOM All things are made of atoms. They are EVERYWHERE! Look around you. EVERYTHING YOU SEE is made up of atoms – the land, sea, walls, other people, the sky…….. 1cm3 of air at sea level (at 0oC) contains about 50 billion billion atoms/molecules. Now think of how many cm3 are in this room…and outside….and in the Universe There are a lot of atoms!

Atoms Are Extremely Durable Every atom in your body has been around since the creation of the Universe. They have passed through several stars and been parts of millions of different animals, plants and rocks before making YOU! Just think…..the atoms in your body were once in the form of a Tyrannosaurus Rex!

What is an atom? An atom is made up of Positive Protons, Negative electrons and NEUTral NEUTrons. Protons Neutrons Electrons Return to menu

What is the structure of the atom? The NUCLEUS contains protons & neutrons. It makes up most of the MASS of the atom – yet it is tiny! The ELECTRONS fly around the outside. They’re negatively charged and really small. They occupy a lot of space and this gives the atom its overall size. (Even though it’s mostly empty space)

What is the structure of the atom? Particle Relative Mass Relative Charge Proton 1 +1 Neutron Electron 1/1840 -1

MASS NUMBER (Number of PROTONS & NEUTRONS) What is Mass Number & Proton Number? MASS NUMBER (Number of PROTONS & NEUTRONS) He 4 2 PROTON NUMBER (Number of PROTONS) Return to menu

Isotopes Isotopes are atoms with the SAME NUMBER OF PROTONS but DIFFERENT NUMBERS OF NEUTRONS Hence they have the same atomic number, but different mass number Most elements have isotopes but there is usually only one or two stable ones

C C Isotopes Carbon-12 and carbon 14 are examples of isotopes. 14 12 6 Unstable Radioactive Isotope Stable Isotope Return to menu

Matter Was Made up of Tiny Solid Spheres Called Atoms The History of the Atom In 1804 John Dalton Said….. Matter Was Made up of Tiny Solid Spheres Called Atoms An Atom!

Later they discovered electrons could be removed from atoms Later they discovered electrons could be removed from atoms. Scientists then believed atoms had a sphere of positive charge with tiny negative electrons stuck in it. Like plums in a plum pudding! Hence the name ‘PLUM PUDDING MODEL’!

Then, Ernest Rutherford tried firing positively charged alpha particles at thin GOLD LEAF FOIL GOLD was used as it could be beaten until it became extremely thin. Ideally Rutherford wanted just 1 layer of atoms for his experiment!

1 in every 8,000 alpha particles bounced back! Rutherford was very surprised by the result. 1 in every 8,000 alpha particles bounced back! It was as if a cannon ball was fired at a sheet of tissue paper and the cannon ball bounced back!

Gold Leaf Alpha Particles Most alpha particles go straight through while others bounce back! The conclusion is that an atom is made up of mostly ‘space’ with a tiny concentrated area of positive charge (the nucleus) in the centre and orbiting electrons. Return to Menu

Nuclear Equations There are 3 equations for EMISSION: Alpha Emission Beta Emission Gamma Emission Make sure your Mass Numbers and Atomic numbers Balance up on both sides!

Ra Rn + He Alpha Emission An Alpha Particle is simply a Helium Nucleus (Mass 4 and charge +2) A Typical Alpha Emission:- Ra Rn + He 226 4 222 86 88 2

A Beta Particle is simple an Electron with NO Mass and a Charge of - 1 Beta Emission A Beta Particle is simple an Electron with NO Mass and a Charge of - 1 A Typical Beta Emission:- e C N 14 14 - 1 7 6

A gamma Ray is a photon with No Mass & No Charge Gamma Emission A gamma Ray is a photon with No Mass & No Charge After an Alpha or Beta Emission the nucleus sometimes gives out an extra bit of energy in the form of a Gamma Ray. Gamma Emission Never changes the Atomic or Mass Numbers.

Nuclear Fission

The Splitting up of Atoms Is Called Nuclear Fission Nuclear power stations and nuclear submarines are both powered by nuclear reactors In a nuclear reactor, a controlled chain reaction takes place in which uranium atoms split up and release energy in the form of heat. This turns water to steam to drive a turbine & generate electricity

Nuclear Fission Nuclear Fission neutron neutron 1 neutron Uranium atom neutron Nuclear Fission Each time a Uranium atom splits up it spits out 2 or 3 neutrons, one of which hits another uranium nucleus, causing it to split. This keeps the chain reaction going.

The Chain Reaction Uranium atom When the Uranium atom splits into two it will form two lighter elements that are also radioactive. This becomes radioactive waste and is a big problem for nuclear power stations as it can remain dangerous for hundreds of years

You may see a chain reaction represented like this: Nuclear Fission It is important to control the numbers of neutrons released otherwise this reaction will become extremely dangerous.We use ‘control rods’ to absorb the unwanted neutrons Return to Menu