particle physics

• what is are nucleons

  protons and neutrons in the nucleus
• charge an mass of proton

  1.60 x10^-19 //1.67x10^-27
• charge and mass of neutron

  0// 1.67x10^-27
• charge and mass of electron

  -1.60x10^-19 // 9.11x10^-31
• what is the nucleon number

  mass number

  how many neutrons and protons in the nucleus

  give a good approx of atoms mass
• what is the proton number

  atomic number

  number of protons in an atom

  proton number tells us alot about its chemical properties
• what is specific charge?

  Specific charge refers to the amount of charge per unit mass of a particle.
• specific charge formula

  charge/mass
• what is a fundamental particle

  a particle which cannot be spilt up into smaller particles
• what is an isotope

  atoms with the same number of protons but a different number of neutrons
• what does changing the number of neutrons affect

  the stability of the nucleus
• what makes an atom unstable

  the greater number of neutrons compared with the number of protons

  this means they may be more radioactive and decay more to become stable
• what is isotopic data

  the relative amounts of the different isotopes of an element present in a substance
• what can isotopic data be used for ?

  carbon dating
• what does gravitational forces do?

  cause all the nucleons in the nucleus to attract each other due to their mass
• why are electromagnetic and gravitational forces not the only forces ?

  The repulsion of the electromagnetic force is much bigger than the gravitational attraction and if there where the only two forces then the nucleons would fly apart
• what is the strong nuclear force

  an attractive force

  stronger than the electromagnetic force
• features of the strong nuclear force?

  short range

  can only hold nucleons together when they are separated up to a few femtometres

  the strength of the strong nuclear force falls quickly beyond this distance

  at small separation it must be repulsive
• what does strong nucellar force do

  it works equally between all nucleons

  size of all forces is the same
• nuclear decay

  its when unstable nuclei will emit particles to become more stable
• when does alpha decay happen

  in very big atoms - more than 82 protons
• why does alpha decay

  when the nuclei of the atom is too big for the strong nuclear force to keep them stable- to become more stable they emit an alpha particle
• what is an alpha particle

  $α_2^4$

  short range in air(few cm)

  causes proton number to decrease by 2 and nucleon number by 4
• how can you see alpha particle range

  observing the tracks left by an alpha particle in a cloud chamber

  use a Geiger counter or spark counter - measures the amount of ionising radiation
• What is beta minus decay

  the emission of an electron from the nucleus along with an antinetrino particle
• when does beta decay happen

  happnes in isotopes that are neutron rich have to many neutrons compared to protons
• what happens in beta decay

  when a nucleus ejects a beta particles one of the neutrons in the nucleus is changed into a proton

  proton num increases by 1

  the antineutrino particle released carries way some E and Momentum
• what did Wolfgang Pauli suggest in 1930

  another particle was being emitted too and it carried away the missing energy

  this particle had to be neutral or charge wouldn't be conserved

  had to have 0 mass
• describe the range of strong nuclear force

  repulsion up to 0.5fm

  attraction between 0.5 -3 fm

  neglible after 3fm
• how was the existance of the neutrino hypothesised ?

  the energy of particles after beta decay was lower than before a particle with 0 charge and negligible mass must carry away this excess energy . this particle was the neutrino
• what is an anti particle ?

  it has the same rest energy and mass of the particle but all other properties are opposite
• anti particle of an electron?

  positron
• antiparticle of a pion (0)

  $\pi^0$ its antiparticle itself
• what occurs when a particle and and antiparticle meet?

  annihilation

  the mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which go in opp directions to conserve energy
• what is pair production?

  a gamma ray photon is converted into a particle - antiparticle pair
• whats the minimum energy of a photon required to make a proton antiproton pair ?

  2 x proton rest enegy

  1876.514 MeV
• name the 4 fundamental forces ?

  Gravity, Electromagnetism, Weak Nuclear Force, Strong Nuclear Force
• what is the exchange particle of strong nuclear force

  gluons

  pions
• what are the exchange particles of electromagnetic force

  photons
• exchange particles of weak nuclear force

  Z

  W+ W boson

  W-