As level physics unit 1 particle physics part b

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ghoran
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238170
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As level physics unit 1 particle physics part b
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2013-10-01 15:40:56
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  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
    1x10^-15m
  5. strong nuclear force on a graph
  6. alpha decay
    • release alpha particles (positively charged helium ions) 
    • reduces mass number of nucleus by 4 and atomic number by 2
    •  
  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 
  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. 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
  11. photons have ... mass and ... charge
    • no 
    • no
  12. the speed of the wave is given by
    • c = f*
    • c = speed of light = 3x10^-8 ms^-1
    • f = frequency = Hz
  13. photons are emitted when
    • fast moving electron stopped
    • electron jumps from higher quantum level (shell) in an atom to a lower one
  14. energy of an electron can be given by
    • E=hf
    • where h = planck's constant = 6.63x10^-34
    • as c = f this can also be written as E=hc/
  15. when a particle and its corresponding anti particle meet they
    annihilate and are converted completely into energy (found by E=mc^2)
  16. 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
  17. 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
  18. 1Mev = ......J
    1.60x10^-13
  19. antiparticle
    • same rest mass as corresponding particle 
    • same rest energy as corresponding particles
    • opposite charge
  20. rest energy of a particle can be found by
    E=mc^2
  21. pair production occurs when
    a photon with a high enough energy changes into a particle and its corresponding anti-particle
  22. 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
  23. Pair creation diagram
  24. annihilation occurs
    when a particle and its corresponding antiparticle meet and convert themselves to energy in the form of two photons
  25. as two photons are produced in annihilation it can be shown :
    • 2E~gamma = 2E~0
    • E=mc^2
    • hf=E~0
  26. annihilation diagram
  27. electromagnetic particle interaction
    • occurs only between charged particles 
    • opposite charges attract 
    • same charges repel 
    • the mediators of the force are virtual photons

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