Topic 10 Flashcards
What is an alpha particle?
A helium nucleus.
What did Rutherford conclude from his results?
• The atom is mainly empty space:
Most particles experience no deflection.
• There is a tiny central nucleus.
Most particles experience no deflection.
• Most of the mass of the atom is contained in the nucleus:
Some of the particles were deflected backwards.
• Nucleus is positively charged:
Alpha particles are deflected through repulsion produce by an electrostatic force.
What is conserved in nuclear transformation?
- Charge
- Total number of protons
- Total number of neutrons
238U92 → 234Th90 + 4He2
Definition: Isotope
Atoms with the same atomic number but different nucleon numbers.
What are the features of an element symbol?
7Li3
7 = Nucleon (mass) number
= number of protons + neutrons
3 = Proton number
= number of protons
Therefore, number of neutrons = 7-3 = 4
What is the process of thermionic emission?
1) A metal is heated and the electrons inside it gain energy.
2) This enables some of them to leave the surface of the metal.
3) They can then be accelerated into a beam via an electric field.
Equation: radius of motion in magnetic field *
r = P / BQ
r = radius (m)
P = mv = momentum (kgms⁻¹)
B = magnetic flux density (T)
Q = charge on particle (C)
Why should the Rutherford scattering experiment be carried out in a vacuum?
So the alpha particles do not collide with any air molecules.
When can’t a particle be detected in a particle detector?
If it has no charge.
How do you justify the direction of a magnetic field?
Fleming’s left-hand rule.
Features: Particle detector
• Electric field:
To provide an electrostatic force on the particles so that they are accelerated from one side to another.
Features: Linear accelerator
• Alternating current:
So every time the particle enters a gap between the cylinders, the polarity of the each cylinder swaps so that the particle is repelled from the previous cylinder and attracted to the next one producing an electric field, causing the particle to accelerate.
• Particles have constant velocity inside cylinders:
Because there is no electric field inside the cylinders meaning the particles aren’t experiencing any force.
• Cylinders increase in length:
As particles travel through the linear accelerator they increase in velocity, meaning the cylinders must get longer so that the particle spends the same amount of time in each tube, so that it remains in time with the frequency of the alternating current.
Features: Cyclotron
• Magnetic field:
To apply a centripetal force to the particle, so that it has circular motion. As the particle gets faster, the radius increases.
• Electric field:
The electric field between the Dee’s provides an electrostatic force on the particles causing it to accelerate.
• Alternating pd:
So that the polarity of each Dee changes every time the particle enters the gap, so that the particle is repelled by the previous Dee and attracted to the next one, meaning that it is accelerated every time it enter the gap.
Equation: Mass and energy
ΔE = c²Δm
ΔE = change in energy (J)
c = speed of light (3.00x10⁸ ms⁻¹)
Δm = change in mass
Cyclotron: Features
• Magnetic field:
To apply a centripetal force to the particle, so that it has circular motion.
• Alternating pd:
So that the particles are accelerated every time they enter the gap between the Dee’s, because the polarity of the Dee’s changes every time the particle enters the gap.
What are the features of an anti-particle?
- Same mass
- Opposite charge
What are some common anti-particles?
Electron / positron
Proton / antiproton
Neutron / antineutron
Quark / antiquark
How do you convert from eV/c² to kg?
1) Convert MeV/c² or GeV/c² to eV (ignore /c²)
2) Convert value to joules.
3) Use m = E / c² to find the mass in kilograms.
What are conserved during decay?
- Charge
- Baryon number
- Lepton number
- Momentum
- Energy-mass
What are hadrons?
Particles which are made of quarks.
Examples:
- Baryon (QQQ)
- Meson (QQ̅)
What are baryons?
Particles made up of 3 quarks.
Examples:
- Protons (uud)
- Neutrons (udd)
What are mesons?
Particles made of one quark and one antiquark.
Examples:
- Pions (ud̅ uu̅ dd̅ d̅u)
- Kaons (us̅ s̅d sd̅ su̅)
What are Pions?
Particles made of up and down quarks. One of which is an anti-quark.
Examples:
- π+ = ud̅
- πo = uu̅ dd̅
- π- = d̅u
What are kaons?
Particles made of strange quarks, with either an up or down quark. One of which is an anti-quark.
Examples:
- K+ = us̅
- Ko = s̅d sd̅
- K- = su̅
What are the different types of quark?
What are leptons?
Fundamental particles which cannot be broken down into anything else.
Examples:
- Muon (µ-)
- Electron (e-)
- Muon-neutrino (vµ)
- Electron-neutrino (ve)
What is the baryon number?
Baryons = +1
Anti-baryons = -1
Non-baryons = 0
Baryon number is always conserved.
What is lepton number?
Leptons = +1
Anti-leptons = -1
Non-leptons = 0
Lepton number is always conserved.
What do the charge of quarks mean?
That many times bigger than the charge of a proton.
2/3 = 2/3 e = 2/3 x (1.6x10-19)
How do you figure out if a decay equation is legitimate?
Check that charge, baryon number, leptop number and strangeness are all conserved.
What are relativistic speeds?
Speeds that are relative to the speed of sound.
Why are massive energies needed during collisions.
To produce anti-particles so that momentum is conserved.
