Topic 8 - Nuclear and Particle Physics Flashcards
What is proton number (Z)?
Number of protons in atom
What is Nucleon number (A)?
Total number of protons and neutrons in atom
What is an isotope?
Nuclide with different nucleon number but same proton number
How did Rutherford’s gold foil experiment give evidence for nuclear model of atom?
- Alpha particles fired at gold foil
- Most alpha particles passed with no deflection suggesting the atom was mostle empty space
- Small amount of particles passed through with slight deflection suggesting that centre was positivily charged
- Some particles were deflected by an angle greater than 90 suggesting centre was very small and dense
What is thermionic emission?
Metal heated until free electrons on its surface gain enough energy and are emitted
How can electrons be accelerated by electric and magnetic fields?
- Electric fields will cause electrons to be accelerated due to diffrence in charge
- Magnetic field will interact with charged particle applying force prependicular to its direction of motion
How do electron guns work?
- Use potential difference to accelerate electrons released by thermionic emission
- Electrons accelerated to anode and pass through gap
How does a cyclotron work?
- Formed of two semi-circular electrodes called Dees with uniform magntic field acting prependicular to the plane of electrodes
- High frequency alternating voltage applied between Dees
- At centre there is a source of charged particles
- Particles are deflected in circular path by magnetic field
- Once particle reaches the edge of a Dee it moves across the gap and accelerated due to electric field
- This increases the radius of circular path
- Particle gain energy equivilent to QV=E
How do Linear accelerators (LINACs) work?
- Formed of several cylindrical electrodes called drift tubes
- Adjecent electrodes are connected to the opposite polarity of an alternating voltage creating an electric field in between the gaps
- At source charged particles are released so that they are accelerated towards first tube
- Length of the tube is calculated so that as the particles pass through the polarity will switch so it can be accelerated to the next
Why is high energy required to investigate the structure of nucleons?
- When investigating nucleons we need to use wavelengths similar to their size
- Nucleons have very small diameter meaning we need very small wavelength
- Wavelength is inversily proportional to momentum (De Broglie)
- Therefore high energy needed
How do particle detectors work?
- Sample vaporised
- Electron gun used to create high energy beam of electrons directed towards sample
- Fast moving electron collide with atoms in vapour causing them to be ionised and therefore charged
- Ions are accelerated using electric field
- Ions pass through velocity selector which has prependicular magntic and electric fields
- Enter seperation chamber which has uniform magnetic field causing ions to follow circular path
- Radius of curved path used to determine mass-to-charge ratio used to identify sample
How to convert between MeV/c^2 and kg?
- Multiply to get MeV to eV
- Multiply by charge of electron to get eV into J
- Divide by c^2 to get into kg
What are the first generation of quarks?
- Up
- Down
What are the second generation of quarks?
- Charm
- Strange
What are the third generation of quarks?
- Top
- Bottom
What is the charge of Up,Charm and Top quarks?
+2/3e
What is the charge of Down,Strange and Bottom quarks?
-1/3e
What is first generation lepton?
electron
What is 2nd generation lepton?
muon
What is 3rd generation lepton?
tau
What are the charges of leptons?
- -e
- Lepton number of 1
What are neutrinos?
- All leptons have associated neutrino
- Neutrinos have lepton number of 1
- Negligble mass
What are antiparticles?
- All particles have associated antriparticle
- Has opposite charge
- Has opposite lepton/baryon number
What are baryons?
- Made of three quarks
- Have baryon number of 1
- What are mesons?
- Made of quark and anti-quark
What are the conservation laws?
- Charge
- Baryon number
- Lepton number
- Strangeness
- Mass-energy
- Momentum
How do bubble and cloud chambers work?
- As charged particles travel through these they leave a trail of ionised atoms
What is annihilation?
- Particle and anti-particle collide
- Produces two photons in opposite direction
- Mass converted into energy
What is pair production?
Photon of great enough energy can decay into electron-positron pair
How does lifetime of particle depend on speed?
- When particles travel closer to the speed of light their properties change
- Their lifetime increases the closer they are to the speed of light due to time dialation
