Going Smaller than Atoms

AQA Syllabus AA Level Physics – Module

2© T Harrison. The National School

Splitting The AtomSplitting The Atom

Electrons

Neutrons Protons

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Splitting The AtomSplitting The Atom

Atoms have a nucleus made up of protons and neutrons.Atoms have a nucleus made up of protons and neutrons.

Protons have a charge of +1.Protons have a charge of +1.

Neutrons have a charge of 0.Neutrons have a charge of 0.

Protons and Neutrons weigh about the same. We give them a relative Protons and Neutrons weigh about the same. We give them a relative mass – their relative mass is 1.mass – their relative mass is 1.

Electrons orbit the nucleus.Electrons orbit the nucleus.

They have a charge of -1.They have a charge of -1.

Electrons are much lighter than nucleons, they weight about a 137Electrons are much lighter than nucleons, they weight about a 137thth of of the mass of a proton. They are given a relative mass of 0. the mass of a proton. They are given a relative mass of 0.

Matter and AntimatterMatter and Antimatter

For every matter particle that exists there is an antimatter copy.For every matter particle that exists there is an antimatter copy.

The antimatter copies have the same mass as their matter The antimatter copies have the same mass as their matter counterparts – that is how you can tell that particle is the anti-counterparts – that is how you can tell that particle is the anti-version of another.version of another.

Other properties, like charge, are reversed.Other properties, like charge, are reversed.

ParticleParticle ChargeCharge

Electron / PositronElectron / Positron -1 / +1-1 / +1

Proton / Anti - ProtonProton / Anti - Proton +1 / -1+1 / -1

Neutron / Anti - NeutronNeutron / Anti - Neutron 0 / 00 / 0

Grouping ParticlesGrouping Particles

Electrons are Fundamental particles. They can’t be split down Electrons are Fundamental particles. They can’t be split down into anything smaller. An electron is one kind of into anything smaller. An electron is one kind of LeptonLepton..

Protons and Neutrons are made up of smaller particles. Protons and Neutrons are made up of smaller particles. These particles are called These particles are called quarksquarks. There are three quarks in . There are three quarks in each proton or neutron.each proton or neutron.

Particles that are made of quarks are called Particles that are made of quarks are called HadronsHadrons. We . We don’t have a group called “Quarks” because you can’t get don’t have a group called “Quarks” because you can’t get quarks on their own.quarks on their own.

Photons (light particles) fit into a third group called Photons (light particles) fit into a third group called Gauge Gauge BosonsBosons..

LeptonsLeptons

Leptons are fundamental particles – remember that means Leptons are fundamental particles – remember that means they can’t be split down into other things.they can’t be split down into other things.

Electrons are one kind of lepton. Neutrinos are another, and Electrons are one kind of lepton. Neutrinos are another, and there are others.there are others.

For some reason there seem to be “copies” of particles that For some reason there seem to be “copies” of particles that have the same properties like charge but have more mass.have the same properties like charge but have more mass.

Electrons have heavier copies called muons and tauons.Electrons have heavier copies called muons and tauons.

Also there are muon-neutrinos and tau-neutrinos.Also there are muon-neutrinos and tau-neutrinos.

In total there are 6 types of lepton.In total there are 6 types of lepton.

QuarksQuarks

There are different types of quarks too. Protons and Neutrons There are different types of quarks too. Protons and Neutrons are made up of “are made up of “upup” and “” and “downdown” quarks.” quarks.

Up quarks have a charge of +Up quarks have a charge of +⅔.⅔.

Down quarks have a charge of -⅓.Down quarks have a charge of -⅓.

Therefore protons consist of two up quarks and a down quark. Therefore protons consist of two up quarks and a down quark. Neutrons are made up of two down quarks and an up quarkNeutrons are made up of two down quarks and an up quark..

Properties of QuarksProperties of Quarks

Charge is a property that particles have. Quarks also have Charge is a property that particles have. Quarks also have another property called another property called ccoolloouurr. They are not really coloured, it . They are not really coloured, it is actually to do with the way that they are “spinning”, but 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.just helps to think of it as if they were coloured.

They come in They come in redred, , blueblue and and greengreen, and have to be grouped , and have to be grouped together to form white – that’s why they come in threes in together to form white – that’s why they come in threes in protons and neutrons.protons and neutrons.

QuarksQuarks

The “colours” of the quarks work The “colours” of the quarks work just like a colour wheel.just like a colour wheel.

Any quark can be any colour, it Any quark can be any colour, it doesn’t matter whether it is the up doesn’t matter whether it is the up or down quarks that are red, green or down quarks that are red, green or blue as long as you have one of or blue as long as you have one of each.each.

So to make protons and So to make protons and neutrons to make up the things we neutrons to make up the things we see around us we need up and see around us we need up and down quarks (which have different down quarks (which have different charges) and we also need three charges) and we also need three different colours. different colours.

More QuarksMore Quarks

Just like there were heavier copies of the electron there are also Just like there were heavier copies of the electron there are also heavier copies of up and down quarks.heavier copies of up and down quarks.

There are “strange” and “charm” quarks, and “top” and “bottom” There are “strange” and “charm” quarks, and “top” and “bottom” quarks.quarks.

These are much rarer but you can make other particles using These are much rarer but you can make other particles using them. These have names like sigma, xi and omega and these them. These have names like sigma, xi and omega and these are similar to protons and neutrons. They all decay after a very are similar to protons and neutrons. They all decay after a very short period of time though. So do neutrons in fact, into protons, short period of time though. So do neutrons in fact, into protons, but the time is longer.but the time is longer.

You can also get anti-quarks. Anti-quarks have the opposite You can also get anti-quarks. Anti-quarks have the opposite charge to their “normal” copy, and also have the “anti-colour”. charge to their “normal” copy, and also have the “anti-colour”. This means that you can make white using less than 3 quarks.This means that you can make white using less than 3 quarks.

Two or Three Quarks?Two or Three Quarks?

We’ve already looked at particles made up from three quarks We’ve already looked at particles made up from three quarks (like protons and neutrons). These are in a sub-group of (like protons and neutrons). These are in a sub-group of Hadrons called Hadrons called BaryonsBaryons..

Particles made of two quarks (a quark and an anti-quark) are Particles made of two quarks (a quark and an anti-quark) are in a sub-group of Hadrons called in a sub-group of Hadrons called MesonsMesons..

Recently particles with 5 quarks have been discovered, but Recently particles with 5 quarks have been discovered, but these live for a very short amount of time.these live for a very short amount of time.

Even these “pentaquarks” are types of Hadron. Hadrons are Even these “pentaquarks” are types of Hadron. Hadrons are special because they interact via the special because they interact via the StrongStrong force. force.

Two or Three Quarks?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.

ForcesForces

Different forces affect different things.Different forces affect different things.

The Electromagnetic force only affects charged objects.The Electromagnetic force only affects charged objects.

The Strong force only affects Hadrons (particles with Quarks in).The Strong force only affects Hadrons (particles with Quarks in).

For each force, there is a particle that “carries” it.For each force, there is a particle that “carries” it.

Photons carry the Electromagnetic force.Photons carry the Electromagnetic force.

Gluons carry the Strong force.Gluons carry the Strong force.

There is also a particle that carries gravity.There is also a particle that carries gravity.

These force carrying particles are called gauge bosons.These force carrying particles are called gauge bosons.

Particle AcceleratorsParticle Accelerators

CERN is a particle CERN is a particle accelerator on the border of accelerator on the border of France and Switzerland. – It France and Switzerland. – It accelerates particles to near accelerates particles to near light speed then crashes light speed then crashes them into each other to find them into each other to find out what they’re made of.out what they’re made of.

The next “big thing” at CERN The next “big thing” at CERN will be the Large Hadron Collider will be the Large Hadron Collider (LHC) estimated for completion (LHC) estimated for completion in 2007. It should be able to find in 2007. It should be able to find new, more exotic, particles.new, more exotic, particles.

Neutrino DetectorsNeutrino Detectors

Superkamiokande is a huge Superkamiokande is a huge detector in Japan built to detector in Japan built to detect neutrinos. It’s part of detect neutrinos. It’s part of a “twin-site” – there is a a “twin-site” – there is a nuclear reactor some nuclear reactor some distance away that distance away that produces a lot of neutrinos.produces a lot of neutrinos.

The K2K experiment helped The K2K experiment helped prove the existence of prove the existence of different types of neutrinos.different types of neutrinos.