1. Going Smaller than Atoms AQA Syllabus A A Level Physics – Module 2 © T Harrison. The National School

2. Splitting The Atom Electrons Neutrons Protons + + _ _ _ _ _

3. Splitting The Atom Atoms have a nucleus made up of protons and neutrons. Protons have a charge of +1. Neutrons have a charge of 0. Protons and Neutrons weigh about the same. We give them a relative mass – their relative mass is 1. Electrons orbit the nucleus. They have a charge of -1. Electrons are much lighter than nucleons, they weight about a 137 th of the mass of a proton. They are given a relative mass of 0.

4. Matter and Antimatter For every matter particle that exists there is an antimatter copy. The antimatter copies have the same mass as their matter counterparts – that is how you can tell that particle is the anti- version of another. Other properties, like charge, are reversed. ParticleCharge Electron / Positron -1 / +1 Proton / Anti - Proton +1 / -1 Neutron / Anti - Neutron 0 / 0

5. Grouping Particles Electrons are Fundamental particles. They can’t be split down into anything smaller. An electron is one kind of Lepton. Protons and Neutrons are made up of smaller particles. These particles are called quarks. There are three quarks in each proton or neutron. Particles that are made of quarks are called Hadrons. We don’t have a group called “Quarks” because you can’t get quarks on their own. Photons (light particles) fit into a third group called Gauge Bosons.

6. Leptons Leptons are fundamental particles – remember that means they can’t be split down into other things. Electrons are one kind of lepton. Neutrinos are another, and there are others. For some reason there seem to be “copies” of particles that have the same properties like charge but have more mass. Electrons have heavier copies called muons and tauons. Also there are muon-neutrinos and tau-neutrinos. In total there are 6 types of lepton.

7. Quarks There are different types of quarks too. Protons and Neutrons are made up of “up” and “down” quarks. Up quarks have a charge of +⅔. Down quarks have a charge of -⅓. Therefore protons consist of two up quarks and a down quark. Neutrons are made up of two down quarks and an up quark.

8. Properties of Quarks Charge is a property that particles have. Quarks also have another property called colour. They are not really coloured, it is actually to do with the way that they are “spinning”, but it just helps to think of it as if they were coloured. They come in red, blue and green, and have to be grouped together to form white – that’s why they come in threes in protons and neutrons.

9. Quarks The “colours” of the quarks work just like a colour wheel. Any quark can be any colour, it doesn’t matter whether it is the up or down quarks that are red, green or blue as long as you have one of each. Any quark can be any colour, it doesn’t matter whether it is the up or down quarks that are red, green or blue as long as you have one of each. So to make protons and neutrons to make up the things we see around us we need up and down quarks (which have different charges) and we also need three different colours. So to make protons and neutrons to make up the things we see around us we need up and down quarks (which have different charges) and we also need three different colours.

10. More Quarks Just like there were heavier copies of the electron there are also heavier copies of up and down quarks. There are “strange” and “charm” quarks, and “top” and “bottom” quarks. These are much rarer but you can make other particles using them. These have names like sigma, xi and omega and these are similar to protons and neutrons. They all decay after a very short period of time though. So do neutrons in fact, into protons, but the time is longer. You can also get anti-quarks. Anti-quarks have the opposite charge to their “normal” copy, and also have the “anti-colour”. This means that you can make white using less than 3 quarks.

11. Two or Three Quarks? We’ve already looked at particles made up from three quarks (like protons and neutrons). These are in a sub-group of Hadrons called Baryons. Particles made of two quarks (a quark and an anti-quark) are in a sub-group of Hadrons called Mesons. Recently particles with 5 quarks have been discovered, but these live for a very short amount of time. Even these “pentaquarks” are types of Hadron. Hadrons are special because they interact via the Strong force.

12. Two or Three Quarks? These four are Baryons. They are either made of three quarks or three anti-quarks. There is no mixing between the two. Notice how the anti- quarks are the “inverted” colour of the quarks. These four are mesons. They are made of a quark and an antiquark.

13. Forces Different forces affect different things. The Electromagnetic force only affects charged objects. The Strong force only affects Hadrons (particles with Quarks in). For each force, there is a particle that “carries” it. Photons carry the Electromagnetic force. Gluons carry the Strong force. There is also a particle that carries gravity. These force carrying particles are called gauge bosons.

14. Particle Accelerators CERN is a particle accelerator on the border of France and Switzerland. – It accelerates particles to near light speed then crashes them into each other to find out what they’re made of. The next “big thing” at CERN will be the Large Hadron Collider (LHC) estimated for completion in 2007. It should be able to find new, more exotic, particles.

15. Neutrino Detectors Superkamiokande is a huge detector in Japan built to detect neutrinos. It’s part of a “twin-site” – there is a nuclear reactor some distance away that produces a lot of neutrinos. The K2K experiment helped prove the existence of different types of neutrinos.