Particles and radiation

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  • Particles and Radiation
    • Atomic structure
      • Nucleon number (mass number)- The number of protons and neutrons in the nucleus. (A)
      • Proton number (atomic number)- The number of protons in the nucleus. Same as the number of electrons. (z)
      • Specific Charge- Ratio of an a particles mass compared to it's charge (CKg-1)
      • Isotopes- Atoms with the same number of protons but a different number of neutrons.
        • Isotopic data-The relative amounts of different isotopes of an element present in a substance
    • Stable and Unstable Nuclei
      • Forces acting on the nucleus are the electromagnetic force, the gravitational force and the strong nuclear force.
        • The strong nuclear force
          • At small separations (>0.5fm) it is repulsive.
          • As separation increases (0.5-3fm) nuclear attraction increases to maximum attraction value and decreases
          • the force extends indefinitely
      • Nuclear Decay
        • Alpha decay
          • Only happens in big atoms as they are too big for the strong force to keep them stable.
          • They emit an alpha particle (4,2 A) from their nucleus.
          • proton number decreases by two, nucleon number decreases by 4.
          • They have a short range. Can be seen in a cloud chamber or detected by a Geiger or spark counter.
        • Beta decay and the hypothesis of neutrinos
          • 1930- Wolfgang Pauli suggested another particle was emitted during as part of beta decay. this took the energy.
      • Beta-minus decay
        • The emission of an electron from the nucleus along with an antineutrino particle.
        • Happens in isotopes that are neutron rich.
        • beta particles have a larger range than alpha particles
        • A neutron becomes a proton, the antineutrino carries away energy and momentum
    • Antiparticles and photons
      • Electromagnetic radiation
        • Radio waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma Rays
          • Down-increasing frequency  Up-increasing wavelength
        • the higher the frequency the higher the energy
      • Photons
        • Einstein suggested EM waves and their energy could only exist as discrete packets of energy called photons
        • Energy of photon= the frequency of light dived by Planck's constant
        • Frequency= speed of light in a vacuum (c)/ Wavelength in m.
      • Antiparticles
        • Each particle has an antiparticle with the same mass and energy but opposite charge.
        • Particles are matter. Antiparticles are antimatter
      • pair production
        • Einstein's theory, energy can turn into mass and mass into energy
        • When energy is converted into mass it creates equal amounts of matter and antimatter.
          • E.g if two protons with a large amount of KE collided a proton and antiproton might form.
        • The minimum energy needed is known as the total rest energy. The minimum energy needed is equal to two times the rest energy of a particle
      • Annihilation
        • Happens when a particle meets it's antiparticle.
        • All the mass is converted back into energy, antiparticles don't exist in normal matter as this happens
          • Minimum energy of photon produced=rest energy of particle type annihilated
        • PET scanners work by putting a positron emitting isotope in the bloodstream and detecting the gamma ray produced by the annihilation that occurs.
    • Hadrons and leptons
      • Hadrons- made up of baryons and mesons
        • particles that feel the strong force are called hadrons
        • Baryons
          • All baryons except a free proton are unstable and so will decay. Eventually to become a proton.
          • Antibaryons- not found in normal matter
          • baryon number- a quantum number that must be conserved
            • proton and neutron B=+1 Antibaryons B=-1       Other Particles B+0
          • Neutron Decay- caused by weak interaction
            • n= p+ e-+ Ve
        • mesons
          • Interact with baryons via the strong force. All mesons are unstable
          • Pions are the lightest meson. There are 3 types, all with different charges
          • Kaons are heavier and more unstable. Have a short lifetime and decay into pions.
          • Detection of mesons Cosmic rays(contain lots of high energy particles) can be observed in a cloud chamber or detected by two Geiger counters with a piece of lead in between.
      • leptons
        • Fundamental particles that don't feel the strong force. They interact with other particles through the weak force
        • Electron, muon and electron neutrino and muon neutrino. Each also have an anti particle
        • Lepton number- a quantum number that must be conserved. Two different types for electron and muon
    • Strange particles and conservation of properties
      • Strange particles
        • Have a property called strangeness, they're created via the strong force in which the strangeness must be conserved.
        • Strange particles decay via the weak force where strangeness can change by 1
      • Conservation of properties
        • Charge must always be conserved
        • Baryon number must always be conserved
        • Lepton numbers must be conserved seperately
        • Strangeness only has to be conserved via the strong force.
    • Quarks and antiiquarks
      • Quarks
        • There are 6 types of quarks, up, down and strange and their antiquarks.
        • A combination of 3 up and down quarks make up protons and neutrons.
        • All mesons are made up of one quark and one antiquark. Only kaons have strangeness
      • Quark confinement- a single quark cannot be confined
      • Weak interaction
        • Beta minus decay- a neutron is changed into a proton. A d quark becomes an up quark.This is known as changing a quarks characteristics
        • Beta plus decay- Unstable isotopes may decay by B+ decay and so a proton becomes a neutron. This means an u quark becomes a d quark.
      • Searching for particles- a theory is created based on observations and then are tested. Due to funds large numbers may have to get together to do this.
  • Particle interactions
    • Repulsion
      • Particles are pushed away from each other as an exchange particle is passed between them as it carries momentum.
    • Attraction
      • As an exchange particle is passed between two particles they are pushed together.
    • Strong force exchange particle is the pion- affects hadrons
    • Electromagnetic exchange particle is the virtual photon and only affects charged particles.
    • The size of the exchange particle determines the range of the force.

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