Nuclear and Particle Physics

Question 1

How can the ball and hill experiment demonstrate the alpha particle scattering experiment.

Answer 1

• Some alpha particles were deflected back completely, or at large angles over 90º.
• This is demonstrated by when the ramp is in line with the centre of the hill, and balls roll up it and back down.
• Some alpha particles were scattered at small angles.
• This is demonstrated when the ramp is moved perpendicularly to its direction so that the ball passes over the edge of the hill, rolling outwards slightly.
• Some alpha particles were negligibly affected
• This is demonstrated when the ramp is moved so the balls don’t pass over the hill at all.

Question 2

What are the key changes made after the gold foil experiment?

Answer 2

• Atom used to be evenly distributed charge/mass
• Now charge and mass is concentrated in a nucleus that is extremely small compared to the size of the atom
• Most of the atom is empty space
• Nucleus is charged

Question 3

How are electrons released from filament?

Answer 3

Thermionic emission

Question 4

How can you interpret particle detector tracks?

Answer 4

• Same direction of curvature: same charge
• Remember conservation of charge between particles
• Path length: half life indication
• No path: no charge
• Smaller radius: less momentum (for same charge)
• Momentum decreases anyway
• If you know the charge, you can work out the momentum using p = Bqr, then use conservation of momentum to work out the momentum of the incoming particle.

Question 5

How can you apply conservation laws to comment on the possibility of a particle equation?

Answer 5

• Baryon number
• Lepton number
• Conservation of charge
• Conservation of mass (calculate ∆m, then ∆E in MeV)
• Conservation of momentum (will be conserved if…)

Question 6

What are characteristics of the lepton family?

Answer 6

• Baryon number = 0
• Lepton number ≠ 0
• Each lepton has an antiparticle
• Leptons are fundamental particles
• They interact via the weak force

Question 7

Describe the different classifications of fundamental particles.

Answer 7

Hadrons:
- Experience strong force
Baryons:
- Three quarks from: up u, down d, top t, bottom b, strange s, charm c, each with a corresponding antiquark (line over top)
- Proton P = uud
- Neutron N = udd
- Lambda Λº = uds
Mesons:
- Baryon number and lepton number of 0
- One quark, one antiquark
- Pion
- Kaon

Leptons:
- Doesn’t experience strong force (weak force)
- tau
- electrons
- muons
- neutrinos

Question 8

Explain why a high-speed particle takes longer to decay than expected.

Answer 8

• Refer to information (actual amount of decays was much less than expected, therefore it actually has a longer lifetime).
• The high speed of the particle has led to relativistic effects.
• This causes time dilation and for the lifetime to increase.

Question 9

What happens because of relativistic effects?

Answer 9

• Time dialtion
• Apparent mass increase

Question 10

Why might taking readings of the activity of a specific element be inaccurate, using a GM tube directed at the sample?

Answer 10

• Radiation absorbed by the GM tube window.
• Radiation absorbed by materials between the source and GM tube.
• Alpha particles will be emitted in all directions, and may not all reach the tube.
• Radiation from decay products may also be detected and unaccounted for.