As level physics unit 1 particle physics part b

  1. the strong nuclear force
    binds nucleons together
  2. there are several different forces acting on the nucleons in the nucleus . the two you already know about are electrostatic forces from the protons' electric charges , and gravitational forces due to the masses of the particles . if you do the calculations you find the repulsion from the electrostatic force is much .... than the gravitational attraction . if these were the only forces acting in the nucleus , the nucleons would ..........
    • bigger
    • fly apart . So there must be a another attractive force that holds the nucleus together - called the strong nuclear force
  3. the strong nuclear force is quite complicated
    • 1) to hold the nucleus together , the strong nuclear force must be an attractive force thats stronger than the electrostatic force 
    • 2) experiments have shown that the strong nuclear force has a very short range . it can only hold nucleons together when they're separated by up to a few fentometers - the size of a nucleus 
    • 3) the strength of the strong nuclear force
    • rapidly falls beyond this distance 
    • 4) experiments have shown the nuclear force works equally between all nucleons . this means that the size of the force is the same whether it's a proton-proton , neutron-neutron or proton-neutron
    • 5) at very small separations , the strong nuclear force must be repulsive - otherwise there would be nothing to stop it crushing the nucleus to a point
  4. 1 femtometer = .... meters
  5. strong nuclear force on a graph
    Image Upload 1
  6. alpha decay
    • release alpha particles (positively charged helium ions) 
    • Image Upload 2
    • reduces mass number of nucleus by 4 and atomic number by 2
    •  Image Upload 3
  7. beta deacy
    • there are two types of beta radiation 
    • beta + 
    • and 
    • beta -
  8. beta - deacy
    • beta - decay is the emission of an electron from the nucleus along with an anti-neutron 
    • beta decay happens in isotopes that neutron rich (i.e. have too many more neutrons than protons in their nucleus)
    • when a nucleus ejects a beta particle , one of the neutrons in the nucleus is changed into a proton an electron and anti-neutrino are emitted 
    • the proton number increases by 1 and the nucleon number stays the same 
    • Image Upload 4
  9. beta + decay
    • neutron deacys into a proton emitting an electron and an electron anti neutrino 
    • the proton number decreases by one and the nucleon number stays the same
  10. Image Upload 5
    Image Upload 6
  11. gamma radiation
    when alpha or beta decay occurs the nucleus is usually left in an excited state it subsequently releases a high energy photon (gamma particle) to reduce this energy
  12. photons have ... mass and ... charge
    • no 
    • no
  13. the speed of the wave is given by
    • c = f*Image Upload 7
    • c = speed of light = 3x10^-8 ms^-1
    • f = frequency = Hz
  14. photons are emitted when
    • fast moving electron stopped
    • electron jumps from higher quantum level (shell) in an atom to a lower one
  15. energy of an electron can be given by
    • E=hf
    • where h = planck's constant = 6.63x10^-34
    • as c = fImage Upload 8 this can also be written as E=hc/Image Upload 9
  16. when a particle and its corresponding anti particle meet they
    annihilate and are converted completely into energy (found by E=mc^2)
  17. it is also possible for a photon of high enough energy to spontabeously change to
    a particle and its antiparticle counterpart ; this is known as pair production
  18. energy of a particle is usually measured in
    Mev and is defined as the energy required to accelerate an electron through the potential difference of 1 volt
  19. 1Mev = ......J
  20. antiparticle
    • same rest mass as corresponding particle 
    • same rest energy as corresponding particles
    • opposite charge
  21. rest energy of a particle can be found by
  22. pair production occurs when
    a photon with a high enough energy changes into a particle and its corresponding anti-particle
  23. as one photon turns into two particles , using E=mc^2 , the photon must have at least the rest energy of the 2 particles that it turns into hence
    • E~0=mc^2
    • (kinetic energy must be added in if given)
    • as 2 particles are produced 
    • 2E~0 = 2(mc^2)
    • therefor the energy of the photon must be 
    • E~gamma=2E~0
    • as E=hf 
    • hf= 2E~0
  24. Pair creation diagram
    Image Upload 10
  25. annihilation occurs
    when a particle and its corresponding antiparticle meet and convert themselves to energy in the form of two photons
  26. as two photons are produced in annihilation it can be shown :
    • 2E~gamma = 2E~0
    • E=mc^2
    • hf=E~0
  27. annihilation diagram
    Image Upload 11
  28. electromagnetic particle interaction
    • occurs only between charged particles 
    • opposite charges attract 
    • same charges repel 
    • the mediators of the force are virtual photons
Card Set
As level physics unit 1 particle physics part b