2. Particles and Radiation

• What is the quark arrangement of Λ0 ?

  uds
• Atoms consist of protons, neutrons (nucleons), and electrons
• Protons and neutrons are in the nucleus, while electrons are in orbitals
• Protons and electrons have equal and opposite charges
• Specific charge is the ratio of charge to mass, applicable to a nucleus or an ion
• An isotope is a form of an element's atom with the same proton number but a different number of neutrons
• Particle information:

  • Proton: Relative Mass = 1, Relative Charge = +1, Mass = 1.6 x 10^-27, Charge = +1.6 x 10^-19
  • Neutrons: Relative Mass = 1, Relative Charge = 0, Mass = 1.6 x 10^-27, Charge = 0
  • Electrons: Relative Mass = 0.0005, Relative Charge = -1, Mass = 9.11 x 10^-31, Charge = -1.6 x 10^-19
• Strong nuclear force acts between nucleons at a short range, holding them together by overcoming electrostatic repulsion between protons
• Types of Decay:

  • Beta minus decay: Neutron turns into a proton, emits an electron and an electron antineutrino
  • Beta plus decay: Proton turns into a neutron, emits a positron and an electron neutrino
  • Alpha Decay: Helium nucleus (alpha particle) is emitted
• Energy of a photon can be calculated using Planck's constant and speed:

  Energy of a Photon = Planck's Constant x Speed / Wavelength

  E = hc / λ
• Antiparticles have the same mass/rest energy but opposite charges and other quantum numbers compared to normal matter counterparts
• Pair Production: A photon interacts with a nucleus, converting its energy into the mass of a particle and its corresponding antiparticle
• Exchange particles are force carriers for fundamental forces, determining the range of the force based on their size
• Classification of Particles:

  • Hadrons interact via the strong nuclear force and are made of quarks
  • Baryons: Made from 3 quarks, decay into a proton
  • Mesons: Made from a quark and antiquark pair
  • Leptons: Fundamental particles that interact only via the weak interaction
• Quarks:

  • Up: Symbol = u, Charge = +2/3, Baryon Number = +1/3, Strangeness = 0
  • Down: Symbol = d, Charge = -1/3, Baryon Number = +1/3, Strangeness = 0
  • Strange: Symbol = s, Charge = -1/3, Baryon Number = +1/3, Strangeness = -1
• Conservation laws:

  • Charge is always indicated by the particle
  • Baryon number is 0 except for baryons which are +1
  • Lμ: 0 except for a muon and muon neutrino which are +1
  • Le: 0 except for an electron and electron neutrino which are +1
  • Strangeness: K+ and Ko are +1, K- and anti-Ko are -1
• The Photoelectric Effect:

  • Described in terms of particles where one electron absorbs one photon
  • Metal emits electrons (photoelectrons) when radiation frequency is greater than the threshold frequency
  • Maximum kinetic energy of photoelectrons increases with incident photon frequency
  • Intensity of radiation affects the number of photoelectrons emitted
• Demonstrations of the photoelectric effect using a photocell and UV radiation
• Electrons exist in discrete energy levels, with ionization and excitation processes
• Fluorescent Tubes:

  • Free electrons collide with mercury atoms, exciting orbital electrons
  • UV photons are released, absorbed by phosphorous coating, emitting visible light photons
• Wave-Particle Duality:

  • Light exhibits wave-like properties in diffraction and particle-like properties in the photoelectric effect
  • Electrons can be diffracted and deflected, showing both wave and particle properties
• • An electron beam transfers some of its kinetic energy to an electron in the gas particle
  • One electron leaves the gas particle

  
• • A neutron changes into a proton
  • This particle is W- because...
  • This is a weak interaction and indication that the charge is conserved

  
• For:

  • Line C is in both hydrogen and helium spectra

  Against:

  • Line D is missing and is in neither the hydrogen or sodium spectra

  
• • Photon is the energy carrier
  • In absorption, the atom becomes excited and moves to a higher energy level by absorbing a photon
  • In emission, the atom de-excites and moves to a lower energy level by emitting a photon

  
• • The graph shows that beta particles have a range of kinetic energies
  • There is a maximum amount of energy released by C-14 so there must be another particle that carries the missing energy away

  
• Loses its charge:

  • Emission of electrons from the surface when EM radiation is incident on the plate
  • Number of surplus electrons remaining on the plate decreases with time

  Frequency:

  • Minimum energy is required
  • A photon must supply this energy in one interaction
  • Minimum energy is the threshold frequency

  Intensity:

  • Increased intensity at the same frequency results in more photons per second incident on the plate
  • Must increase the number of photons per second even if the frequency increases
  • More electrons released from plate every second so loses charge more rapidly

  
• • Q
  • Diffraction as the electron moves between the layers in the graphite

  
• • momentum of electrons increases
  • wavelength is inversely proprotional to speed

  
• Wavelength comparison:

  • Red LED will emit longer wavelengths than 660nm
  • Blue LED will emit longer wavelengths than 440nm

  Excitation process:

  • Photons are absorbed by atoms in coating
  • Atoms are excited
  • Atomic electrons move to energy levels higher than n = 2
  • Photons have sufficient energy to promote electrons to high enough levels

  De-excitation process:

  • Photons are emitted by atoms in coating
  • Atoms de-excite
  • Atomic electrons move to lower energy levels
  • Electrons move to ground state via other energy levels
  • Emitted radiation consists of lower phton energies

  
• • Weak interaction so strangeness can change by 0, +1 or -1
  • $K^+$$-->μ^+$$+$$ve$

  
• State and explain which interaction is involved in this decay [2]

  $Λ^0 --> π^0+$$n$

  • Strangeness changes in this decay
  • Therefore it is the weak interaction