Nuclear physics

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  • Created by: Sagaana
  • Created on: 21-01-20 20:33
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  • Nuclear Physics
    • Nuclear Radius and Density
      • Nucleus made up of protons and neutrons
        • Nucleon= number of nucleons
      • Electron Diffraction
        • electron = lepton don't interact with strong nuclear force allowing them to get a more accurate method for estimating the nuclear radius
          • the moving electron has an de broglie wavelength
            • The electrons wavelength must be tiny for to investigate the nuclear radius meaning that electron will have a high energy
              • diffraction pattern can be seen for this high energy electron and the distance  to the first minimum will be the radius
        • Intensity of the maxima decreases as the angle of diffraction increases
        • The central brightness contains most of the incident electrons which is surrounded by other dimmer rings.
      • Radius of an atom = 0.05nm
      • Radius of the Smallest nucleus = 1fm
      • Nuclear Radius is Proportional to the cube root of the Nucleon Number
      • volume for both proton and neutrons  is same
        • they also have nearly the same mass meaning that they have a similar density
          • Nuclear Density = 1.45 * 10^17
    • Radioactive Emissions
      • Radioactive decay = nucleus decays by releasing energy and/or particles which is cause by instability
        • This is random and cannot be predicted
      • When a radioactive particle hits an atom it can knock off electrons creating an ion = ionising radiation
      • 4 Types of Nuclear Radiation
        • Alpha
          • strongly ionising
          • Can be stopped by few cm of air
          • slow
          • Happens in Heavy Nuclei
        • Beta-minus
          • Weakly Ionising
          • Can be stopped by 3mm aluminium
          • fast
          • Happens in  Neutrons Rich Nuclei
        • Beta-plus
          • annihilated by electron so 0 range
          • fast
          • Happens in  Proton Rich Nuclei
        • Gamma
          • Very Weakly
          • Stopped by many cm of lead or several m of concrete
          • speed of light
          • Obeys the Inverse square law
            • Distance yourself from a radioactive source and handle source with tongs
          • Happens when there is Nuclei with too much energy.
      • Uses
        • Controlling the thickness of the paper(Beta radiation)
        • smoke alarm(Alpha radiation)
        • Radioactive traces (Gamma Radiation)
          • Risk?
            • Cells can mutate
            • Cell death
            • bone marrow destruction
            • Hair Loss
            • change in genetic material
            • Sterility
            • Skin burns
      • Background Radiation
        • radon gas
        • rocks
        • Cosmic Radiation
        • Living Things
        • Man-made e.g Nuclear bomb testing.
    • Exponential Law of Decay
      • Different Isotopes Decays at Different Rates
        • Rates of Decays are measured by  Decay Constant
      • half life = The average time that it takes for number of a unstable nuclei to halve
        • This is a exponential decay.
      • Half lives have different uses
        • Radioactive dating of objects activity of Carbon -14 falls after death
        • medical traces have a short half life which is means that patients wont have long exposure.
    • Nuclear Fission and Fusion
      • Fission
        • Occurs when a nucleus splits into two equal fragments
        • Can cause a Chain Reaction
        • The fragments repel each other as they are both positively charged
          • They gain KE
            • The fission neutrons also gain KE
              • This equals the change of binding energy
            • This equals the change of binding energy
      • Fusion
        • takes place when two nuclei combine to form a bigger nucleus
        • The binding energy per nucleon of the product is greater than of the initial nuclei
        • energy released equal to the increase of binding energy.
        • Can only if the two nuclei that are to be combined collide at high speed this is necessary to over come electrostatic repulsion so they can come close enough to interact through strong nuclear
      • Nuclear Reactor
        • Moderator
          • This slows down neutrons to thermal speeds through elastic collisions
          • Closer the moderator atoms are in size to a neutron.The larger the proportion of momentum which transferred
            • lower number of collisions are required to get neutrons to thermal speeds
          • Water is most often used at the moderator.Graphite can also be used sometimes.
        • Control Rod
          • They absorb neutrons in the reactors to control the chain reactions
          • The height of the control rods can be controlled to control the amount of energy produced
          • They are often made of boron.
        • Coolant
          • This absorbs the heat that is released during fission reactions in the core of the reactor
          • This heat is used to create steam which powers the turbines
          • again water is used as the coolant as it has a high specific heat capacity
    • Binding Energy
      • energy released = the difference of mass before and after
      • The total energy after the change is always less than the total mass before the change
        • the mass is converted into energy
      • work must be done to separate every nucleon
        • this work is done to overcome the strong nuclear force.
          • The potential  energy of each nucleon  increase as work is done on it to remove it from the nucleus
      • Energy is released when pulling nucleons together = binding energy
        • mass of nucleus is less then the mass of the separated nucleons

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