P2b Topic 5 - Nuclear Fission and Nuclear Fusion

Question 1

Radioactivity is a

Answer 1

Totally random process

Question 2

Alpha particles are

Answer 2

1) Helium nuclei.
2) They’re made up of 2 protons and 2 neutrons.
3) They’re big, heavy and slow moving.
4) They have a strong positive charge.
5) Strongly ionising. Weakly penetrating.

Question 3

Beta particles are

Answer 3

1) Electrons are emitted from the nucleus.
2) Quite fast and quite small.
3) Negative charge.
4) Moderately ionising and penetrating.
5) For every beta-particle emitted, a neutron turns to a proton in the nucleus.

Question 4

Gamma rays are

Answer 4

1) A type of electromagnetic radiation.

2) Weakly ionising. Strongly penetrating.

Question 5

Alpha particles are blocked by

Answer 5

Paper, cardboard, skin

Question 6

Beta particles are stopped by

Answer 6

Thin aluminium, a thin sheet of any metal

Question 7

Gamma rays are stopped by

Answer 7

Thick lead and concrete

Question 8

Stages in fission

Answer 8

1) A slow moving neutron is fired at Uranium 235. The neutron is absorbed by the nucleus - this makes the atom unstable and causes it to split.
2) When the U-235 splits it forms two lighter elements and releases thermal energy.
3) Each time a uranium atom splits up, 2 or 3 neutrons are also released. These can hit into other uranium nuclei causing them to split also creating a chain reaction.

Question 9

How to control chain reactions

Answer 9

1) Fuel rods capture slow moving neutrons.
2) The fuel rods are placed in a moderator to slow down the fast moving neutrons.
3) Control rods, often made of boron, limit the rate of fission by absorbing excess neutrons. These can be raised and lowered to control the chain reaction.

Question 10

In nuclear fusion..

Answer 10

1) Two lighter nuclei collide together at high speed and fuse to create a larger nucleus.
2) Fusion releases a lot of energy (more than fission for any given mass).
3) All the energy released in stars come from fusion.
4) Fusion doesn’t leave behind a lot of radioactive waste and there’s plenty of hydrogen around to use as fuel.

Question 11

Fusion only happens at

Answer 11

High temperatures and pressures

Question 12

Isotopes are atoms

Answer 12

With the same number of protons in their nucleus, but a different number of neutrons