3.2 Particles and Radiation

3.2 Particles and Radiation

1. 3.2.1.1 Constituents of the Atom

   • Specific Charge = Charge / Mass
     • E.g. Specific Charge of Proton:
   • Total Number of Protons and Neutrons is known as Nucleon Number
   • Nuclide Notation
   • Isotopes are elements with different number of neutrons but the same amount of protons.

2. 3.2.1.2 Stable and Unstable Nuclei

   • Holds the nucleus together, which should separate due to the electrostatic force of repulsion of protons.
     • Repulsive below 0.5fm
     • Attractive 0.5fm < x < 3fm
   • Strong Nuclear Force
   • Radioactive Decay

3. 3.2.1.3 Particles, Antiparticles and Photons

   • For every particle, there is a corresponding antiparticle
   • EM Waves are emitted by a charged particle when it loses energy. They are emitted as short bursts of waves, each burst is a package called a photon.
     • Photon Energy:
       • E = hf
         • Where h = the Planck constant, 6.63 x 10^-34 and where f is frequency of photons
         • Or E = hc/ƛ
   • When matter and its corresponding antimatter meet, annihilation occurs. This is when their mass is converted into energy, releasing 2 photons.
     • 2 photons are produced to ensure total momentum is conserved.
       • 1eV = 1.60 x 10^-19 J
   • Pair production is the production of mass in the form of a particle and antiparticle from a photon

4. 3.2.1.4 Particle Interactions

   • Forces between particles are explained by exchange particles, which allow the interaction to happen.
     • The weak nuclear force is involved in radioactive decay. It is weaker than the strong nuclear force since it doesn't affect stable nuclei.
       • The weak nuclear force causes positron emission, or beta+ decay. This involves a proton turning into a neutron in a proton-heavy nucleus. A positron and neutrino are then emitted.
         • W+ or W- bosons are the transfer particle for this.
       • In electron capture, an electron in the inner shell is captured by the nucleus, in which a proton turns into a neutron and a neutrino is ejected from the nucleus.
     • Feynman Diagrams can be used to represent the interactions.

5. 3.2.1.5 Classification of Particles

   • Hadrons are one type of particle. They are split into baryons and mesons. Hadrons interact through the strong interaction. Apart from the proton which is already stable, hadrons eventually decay into the proton.
     • Baryons are large particles made up of 3 quarks. Baryons include protons in their decay products.
     • Mesons
       • Mesons are made up of a quark and antiquark. They do not include protons in their decay products.
   • Leptons are fundamental particles, meaning they are not made up of quarks. Examples are the electron, the muon and the neutrino. Leptons interact through the weak interaction (and not the strong).
   • Kaons are produced through the strong interaction and decay through the weak interaction. This has lead to them being called strange particles. They are always created in pairs.

6. 3.2.1.6 Quarks and Antiquarks

   • Protons are made from uud quark combination.
     • Antiprotons are made from 2 anti up, and an antidown quark combination.
   • Neutrons are made from udd quark combination.
   • In Beta- decay, a down quark changes to an up quark. In Beta + decay, an up quark changes to a down quark.

7. 3.2.1.7 Applications of Conservation Laws

   • In any interaction, energy, momentum, baryon number, lepton number, charge and strangeness are conserved.

8. 3.2.2.1 The Photoelectric Effect

   • When EM Radiation above a certain frequency is directed at a metal surface, electrons are emitted from the metal surface.
     • The frequency that the radiation must be above to cause photoelectric emission is called the threshold frequency.
       • If below the threshold frequency, no photoelectric emission will occur.
         • The work function of a metal is the minimum energy needed by an electron to escape the metal surface. Any excess energy is used as kinetic energy by the electron.
     • The number of electrons emitted per second is proportional to the incident radiation.
     • Photoelectric emission occurs without delay.

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