8. Nuclear and Particle Physics

Question 1

What is the nucleon number and where is it found?

Answer 1

It is the number of protons and neutrons that an atom has and it is typically the top number on an element on the periodic table.

Question 2

What is the proton number and where is it found?

Answer 2

It is the number of protons that an atom has and it is typically the bottom number on an element on the periodic table.

Question 3

Describe the plum pudding model.

Answer 3

The idea that an atom is a large ‘cakey’ mass with ‘negative plums’ dotted around it.

Question 4

How did Rutherford’s experiment disprove the plum pudding model and what model replaced it?

Answer 4

The fact that very few alpha particles were deflected through angles greater than 90 degrees showed that there had to be a dense, positively charged nucleus which lead to the nuclear model.

Question 5

What three things were observed in Rutherford’s experiment?

Answer 5

• Most alpha particles weren’t deflected when passing through the foil - this proves that the gold foil was mostly empty space (and doesn’t have uniform density as suggested by the plum pudding model.
• A small amount of particles were deflected through a small angle (<90*) - this proves that the centre of the atom was positively charged therefore repelling the positively charged alpha particles.
• Very few particles were deflected through a large angle (>90*) - this suggests that the centre of the atom is very dense therefore allowing it to deflect fast moving particles but also that its very small hence the few particles deflected.

Question 6

Define thermionic emission.

Answer 6

The heating of a metal until the electrons on the surface receive enough energy to be emitted.

Question 7

Name the two types of particle accelerators and the fields that they use.

Answer 7

• Linear accelerators (LINAC) - makes use of an electric field to accelerate electrons
• Cyclotron - uses a magnetic field and an alternating electric field

Question 8

Explain why the drift tubes in a LINAC progressively get longer.

Answer 8

With each pass between drift tubes, the particle is being accelerated, and covers more and more ground per second. Therefore, the drift tubes must get longer and be placed farther apart.

Question 9

Derive the equation for r=mv/BQ

Answer 9

F = mv^2 / r
F = Bqv

mv^2/r = Bqv
mv/r = Bq
r = mv/BQ