Chapter 26 - Particles

Question 1

Explain how nuclear fission can lead to a chain reaction [3 marks]

Answer 1

• Nucleus splits - Releasing neutrons - Which are absorbed by different uranium nuclei

Question 2

Nuclear fission releases energy; explain the form that this energy takes [2 marks]

Answer 2

• Kinetic energy of particles - Of (fission) products / (daughter) nuclei / neutrons

Question 3

The pressurised water acts as a coolant. It also acts as a moderator. What is the purpose of a moderator? [1 mark]

Answer 3

• To slow down neutrons

Question 4

Answer 4

Question 5

Suggest why Geiger and Marsden removed the air from the apparatus of the goil foil experiment (1)

Answer 5

• alpha has a small range in air
• alpha would not hit the gold leaf
• alpha would be deflected
• alpha would collide with the air {particles/molecules/RA}
• alpha would ionise the {air/ particles/molecules}

Question 6

Describe Geiger and Marsden’s results (2)

Answer 6

• most went (straight) through
• (the paths of) a few were deflected at an acute/small angle
• (the paths of) very few were {deflected through an obtuse angle / backscattered};

Question 7

Rutherford produced a model of the atom. Describe how Rutherford’s model explains Geiger and Marsden’s results. (4)

Answer 7

• Small nucleus
• Mostly empty space
• Because not many α deflected / because most α go straight through
• Positive nucleus
• which causes deflection of positive (or low mass) α

Question 8

Describe what happens when nuclear fission of uranium occurs (3)

Answer 8

• neutron absorbed by (U) nucleus
• (U nucleus) splits;
• (producing 2) daughter nuclei;
• extra neutrons released;

Question 9

The daugter nuclei move off with high speed. Name the type of energy that this gives them. (1)

Answer 9

• Kinetic

Question 10

What start the fission process in a nuclear reactor (1)

Answer 10

• Free neutrons

Question 11

After free neutrons start the fission process, what happens (2)

Answer 11

• Atoms producd then collide with other atoms
• causing the temperature to in the reactor to rise

Question 12

What is the purpose of a moderator (3)

Answer 12

• Made of graphite or water
• Slows neutrons so that they can succesfully collide with uranium nuclei,
• to sustain the chain reaction

Question 13

What is the purpose of control rods (2)

Answer 13

• Often made of boron
• Limit the rate of fission by absorbing excess neutrons

Question 14

What gas is pumped through the reactor, and why (2)

Answer 14

• Carbon dioxide
• To carry away the heat generated

Question 15

After carbon dioxide is pumped through, what are the final stages in a nuclear reactor (7)

Answer 15

• Gas then passed through a heat exchange
• Where it gives its energy to water
• This water is heated
• turns to steam
• which turns a turbine
• which turns a generator
• which produces electricity