Chapter 24- Particle physics

• When two opposite particles they completely destroy each other in a process called annihilation where the masses of both particles are converted into a pair of high energy pair of photons.
• The antiparticle of the electron is the positron
• The four fundamental forces are;

  • strong nuclear
  • electromagnetic
  • weak nuclear
  • gravitational
• The strong nuclear force is experienced by nucleons with a relative strength of 1 and a very short range ~ 10^-15 m
• The weak nuclear force is responsible for beta-decay with a relative strength of $10^{-6}$ and a very short range ~$10^{-18}$m
• The gravitational force is experienced by all particles with mass has a relative strength of $10^{-40}$ and an infinine range
• Subatomic particles are classified into either hadrons and leptons
• Hadrons are particles and antiparticles that are affected by the strong nuclear force. If charged they also experience the electromagnetic force. Hadrons decay by the weak nuclear force. Any particle that contains quarks is a hadron
• Examples of Hadrons include; protons, neutrons and mesons
• Leptons are particles and antiparticles that are not affected by the strong nuclear force. If charged they also experience the electromagnetic force
• Examples of Leptons include electrons, neutrinos and muons
• A fundamental particle is a particle that has no internal structure and hence cannot be divided into smaller bits
• Up quarks have a charge of +$\frac{2}{3}$ and anti-up quarks of a charge of -$\frac{2}{3}$
• Down quarks have a charge of -$\frac{1}{3}$ and anti-down quarks have a charge of +$\frac{1}{3}$
• Strange quarks have a charge of -$\frac{1}{3}$ and anti-strange quarks have a charge of +$\frac{1}{3}$
• Individual quarks within a hadron are bound together by the strong nuclear force. The force is so strong that it may not be able to separate the individual quarks
• A proton consists of three quarks - up, up and down. The total charge of the proton is the sum of the individual charges of the quarks.
• A neutron consists of three quarks - up, down and down. The total charge of the neutron is zero
• Baryons are hadrons that are made up with a combination of three quarks. E.g. protons, anti-protons and neutrons
• Mesons are hadrons made up of a quark and an anti-quark.
• Neutrinos are fundamental particles that carry no charge and may have a tiny mass. They are leptons and exist in abundance in our universe. They do not interact with matter much
• In beta minus decay and unstable nucleus decays into a proton, electron and electron antineutrino. Everything is conserved in this process
• In beta positive decay a proton decays into a neutron, a positron and an electron neutrino.
• In beta minus decay one of the down quarks becomes an up quark and in the process an electron and an electron antineutrino are emitted. The charge on both sides of the equation is -1/3e
• In beta positive decay one of the up quarks becomes a down quark and in the process a positron and an electron neutrino are emitted. The total charge on both sides of the equation is +$\frac{2}{3}$$e$