6.4 nuclear and particle physics

• coulombs law states that any two point charge exert an electrostatic force on each other that is directly proportional to the product of their charges and inverse proportional to the square of their separation
• an isotope is a nuclei of the same element with the same number of protons but different number of neutrons
• nucleon number is the number at the top and it represents the total number of protons and neutrons
• the atomic number is at the bottom which represents the proton number and also the electrons number
• the radius of a nucleus depends on the nucleon number of nucleus
• strong nuclear forces act on hadrons and holding the nuclei together
• a positron is the anti-particle of an electron and so has a positive charge
• 4 fundamental forces are strong and weak nuclear, electromagnetic and gravitational
• electromagnetic forces are experienced by static and moving charged particles
• weak nuclear forces are responsible for beta decay
• gravitational forces are experienced by all particles with mass
• hadrons are particles or antiparticles that is affected by the strong nuclear forces. they are made up by quarks.
• a lepton is a fundamental particles or antiparticles that is affected by weak nuclear forces
• examples of hadrons are mesons, baryons, protons and neutrons
• examples of leptons are electron, muon, tau and neutrinos
• protons are up up down quarks
• neutrons are up down down quarks
• baryons are any hadrons made with a combo of three quarks, protons and neutrons
• mesons are the hadrons made with a combo of quark ad antiquarks
• in beta negative decay a neutron in an unstable nucleus decays into a proton, electron and electron antineutrino
• in beta positive decay a proton decays into neutron, positron and electron neutrino
• alpha radiation consists of positivity charged particles A helium nucleus and has a charge of +2e
• beta radiation consists of fast moving electrons or positrons
• gamma radiation consists of high energy photons with wavelengths less that 10^-13. They carry no charge and travel at the speed of light
• due to their large mass and charge alpha particles interact with surrounding particles ro create a strong ionisation and therefore have a very short range (thin paper)
• due the larger mass and charge beta particles are less ionising and have a longer range (aluminium or 1m in air)
• due to no charge gamma has even less ionising and can be absorbed by few cm of lead
• annihilation is the complete destruction of particles and antiparticles in an interaction that releases energy in the form of identical photons
• pair production is the replacement of a single photon with the corresponding particle and antiparticle of the same total energy
• in annihilation with an electron and positron 2 gamma photons are produced
• carbon dating is a method for estimating the age of organic material by comparing the activities, or the ratios of carbon-14 to carbon-12 nucleus of the dead material of interest
• in alpha decay it emits an alpha particle and the loss of the particle removed two protons and two neutrons from the parent nucleus.
• half life is the average time taken for half the number of active nuclei in a sample of an isotope to decay
• half life is random because we cannot predict when a particular nucleus in a sample will decay and also because each nucleus within a sample has the same chance of decaying per unit of time
• half life is spontaneous because the decay of the nuclei is not affected by the presence of other nuclei in the sample and external factors such as pressure
• the probability of decay governs how quickly the nuclei decay and therefore the half life of the isotope
• the activity of a source is the rate at which nuclei decay or disintegrate
• decay constant is the probability of decay of an individual nucleus per unit time
• to figure out the number of neutrons in nuclear fission is 3 x the number of generations