Radiation

Question 1

What are the advantages of using nuclear power as a resource for the future?

Answer 1

1) Nuclear power stations do not produce carbon dioxide, so they do not contribute to climate change.
2) Supplies of nuclear fuel will last longer than supplies of fossil fuels.

Question 2

What are the disadvantages of using nuclear power as a resource for the future?

Answer 2

1) It is difficult and expensive to store nuclear waste safely.
2) An accident in a nuclear power station can spread radioactive material over a large area.
3) Many people think that nuclear power is dangerous and do not want nuclear power stations to be built.

Question 3

What happens in a fission reaction?

Answer 3

A large unstable nucleus splits into two smaller ones. For example, a uranium-235 nucleus splits up when it absorbs a neutron. The fission of uranium-235 produces two daughter nuclei, two or more neutrons, and also releases energy. The daughter nuclei are also radioactive.

Question 4

How can fission cause a chain reaction?

Answer 4

The neutrons released by the fission of U-235 may be absorbed by other nuclei. Each of these nuclei may undergo fission, and produce even more neutrons. This is called a chain reaction. If a chain reaction is not controlled there will be a nuclear explosion.

Question 5

What happens in a fusion reaction?

Answer 5

Nuclear fusion happens when small nuclei join to form larger ones. Like all nuclear reactions, fusion reactions release energy.

Question 6

What does nuclear fusion require?

Answer 6

Very high temperature and pressure.

Question 7

What does nuclear fission require?

Answer 7

A slow-moving neutron to be absorbed.

Question 8

What is a similarity between fusion and fission?

Answer 8

Both processes release large quantities of energy.

Question 9

What is the role of control rods in a nuclear reactor?

Answer 9

The control rods absorb neutrons. If the control rods are pushed down into the core, more neutrons are absorbed and the chain reaction slows down. If they are pulled out, fewer neutrons are absorbed and the chain reaction speeds up.

Question 10

What is the role of the moderator in a nuclear reactor?

Answer 10

The moderator is a material (often graphite or water) that is used to slow down the neutrons so that fission of the uranium-235 can occur. When a fast neutron hits the nucleus of a moderator atom, it bounces off. Each collision transfers some of the neutron’s kinetic energy to the moderator nucleus and slows down the neutron.

Question 11

What are the uses of gamma rays?

Answer 11

1) Kill cancer cells - beams of gamma rays can be directed at cancer cells to kill them.
2) Sterilise surgical instruments - gamma rays can be used to sterilise plastic instruments which cannot be sterilised by heating.
3) Diagnose cancer - a tracer solution containing a radioactive isotope that emits gamma rays is injected into the body and taken up by cells which are growing abnormally. The places in the body where tracer collects are detected with a ‘gamma camera’.
4) Preserve food - food irradiated with gamma rays will last longer as microbes are killed by the high energy gamma rays. The food does not become radioactive.

Question 12

What is a use of alpha particles?

Answer 12

Smoke alarms:
In the smoke detector, americium-241 is used as an alpha source that gives off a constant stream of alpha particles. The alpha particles ionise the air which creates a small but steady electric current flowing between two electrodes. When smoke enters the chamber, smoke particles attach to the ions which disrupts the ion flow, reducing the current. The alarm detects this drop and triggers the siren.

Question 13

Why are alpha particles used in smoke alarms?

Answer 13

Alpha particles are used because they ionise the air very effectively, making them ideal for generating current. They also cannot penetrate the plastic casting so they are safe when sealed inside the detector. Finally, only a very tiny amount of americium needs to be used.

Question 14

What is a use of beta particles?

Answer 14

Controlling the thickness of paper:
A beta source is placed on one side of the paper. A detector is placed on the other side. Thin paper lets more beta particles through; thick paper blocks more. The machine adjusts the rollers to keep the thickness correct.

Question 15

Why are beta particles used to control the thickness of paper?

Answer 15

Alpha particles would not go through the paper at all. Gamma rays would pass through the paper too easily and the amount getting through would hardly change with small changes in the thickness of the paper.

Question 16

What are the difficulties of nuclear fusion?

Answer 16

Nuclei need to get very close to each other before fusion can happen. Under normal conditions, the positive charges on nuclei repel each other. This is called electrostatic repulsion. Only at very high temperatures and pressures are the nuclei moving fast enough for them to overcome this electrostatic repulsion.