What is a positron?
Positrons are antileptons so Le = -1 for them. They have identical mass to electrons but they carry a positive charge.
What are antiparticles?
Each particle type has a corresponding antiparticle with the same mass but with opposite charge.
Draw a table with the headings symbol,charge, B, Le, for a particle and then the same table for the antiparticle.
Then fil out the tables for following particles and their antiparticles:
proton, neutron , electron and electron neutrino.
The table can be found on page 62 of OCR book.
When energy is convertered into mass you have to make equal amounts of what?
Equal amounts of matter and antimatter.
Explain pair production through the example of two high energy protons colliding into each other.
Fire two protons at each other at high speed and you'll end up with a lot of energy at the point of impact. This energy can form more particles.
If an extra proton is created, there has to be an antiproton made to go with it. It's called pair production.
When will pair production only occur?
Pair production only happens if one gamma ray photon has enough energy to produce that much mass. It also tends to happen near a nucleus, which helps conserve momentum.
Why are electron-positron pairs usually produced from the photons?
Electron-positron pairs are usually produced because they have a relatively low mass.
Draw a diagram of an electron-positron pair coming from a photon.
Why are the particle tracks curved in some diagrams(like diagram on page 63)?
The particle tracks are curved because there's usually a magnetic field present in particle physics experiments. They curve in opposite directions because of the opposite charges on the electron and positron.
An eletron and positron are produced from a single photon. Find the minimum energy of the photon. ( The rest mass of an electron me = 9.11 x 10-31kg.)
Energy before = Energy after
So the energy of the photon > 2mec2 = 2 x 9.11 x 10-31 x (3x108)2
= 1.64 x 10-13J
= 1.0 MeV
What is annihilation?
When a particle meets its antiparticle the result is annihilation.
What happens to the particles in annilihation?
All the mass of the particle and antiparticle gets converted to energy.
Why are there not many antiparticles present?
In ordinary matter antiparticles can only exist for a fraction of a second before this happens, so you won't see many of them.
What type of radiation is released when an electron and positron annihiliate?
The electron and positron annihilate and their mass is converted into the energy of a pair of gamma ray photons.
Draw the electron and positron annihiliation.
- mass is convertered into the energy of a pair of gamma ray photons.