Radioactivity

Question 1

What is the activity of a radioactive source?

Answer 1

The number of atoms that decay every second

Question 2

What is the unit for activity?

Answer 2

Becquerel (Bq)

Question 3

What is the half life of a radioactive isotope?

Answer 3

The time it takes for half of the unstable atoms to decay

Question 4

Why is ionising radiation dangerous?

Answer 4

Mutation:
- Energy transferred by ionising radiation removes electrons from atoms to form ions
- Ions are very reactive and cause mutations to the DNA in cells
- Damage to DNA can lead to cancer
Radiation burns:
- Can also cause damage to self tissue in the form of radiation burns
- When its energy is high enough it can also kill cells

Question 5

What are the precautions when coming into contact with ionising radiation?

Answer 5

• Limiting the time of exposure
• Wearing protective clothing, wearing a lead apron will absorb a lot of the ionising radiation
• Increasing the distance from the person to the radioactive source

Question 6

What are medical tracers?

Answer 6

Substances that are used in biological processes in the body and contain a radioisotope

Question 7

How are medical tracers used?

Answer 7

- They can be eaten, drunk or injected into the body
- The ionising radiation emitted by the tracer can be detected and the biological processes monitored
- Doctors content diagnose the nature and location of any health problems

Question 8

How do PET scanners work?

Answer 8

• The tracer is a radioactive material that decays quickly by emitting positrons
• When positrons come into contact with electrons in the body the two particles annihilate each other
• This results in the formation of gamma rays
• These gamma rays are detected by the PET scanner and processed by a computer, an image is then displayed on the screen
• As the tracers decay quickly, they need to be produced close to where they are used

Question 9

How are tumours treated internally?

Answer 9

• A radioactive source is injected or eaten/drunk by the patient
• It then targets the tumour without affecting the cells around it too much

Question 10

How are tumours treated externally?

Answer 10

• Several beams of gamma rays are fired from different positions towards the cancer
• Each beam isn’t energetic enough to kill the tumour but damages it
• By moving the beam, the amount of ionising radiation received by the surrounding tissue is reduced

Question 11

What are the steps of generating energy within a nuclear power station?

Answer 11

• Fuel rods containing uranium undergo nuclear fission, thermal energy is released
• A coolant (water) is pumped through the reactor, thermal energy from nuclear fission is taken by the coolant to heat water to produce steam 
• The steam causes turbines to rotate which turn the generator to generate electricity
• The steam is cooled back into water in the condenser so it can be used again
• Extra thermal energy is released from cooling towers or into the sea

Question 12

What is the role of the moderator in a nuclear power station?

Answer 12

• It slows down the neutrons so that fission can occur
• It is often graphite or water

Question 13

What is the role of control rods in a nuclear power station?

Answer 13

• They absorb excess neutrons
• Lowering a control rod reduces fission reactions as they will absorb more neutrons

Question 14

How do you prevent stray neutrons and radiation from escaping the core?

Answer 14

Concrete shielding

Question 15

How big is a typical atom?

Answer 15

10^-10m

Question 16

How big is a typical molecule?

Answer 16

10^-9m

Question 17

How big is the diameter of a typical nucleus?

Answer 17

10^-15m

Question 18

How far can alpha particles travel in air?

Answer 18

Less than 5 cm

Question 19

How far can beta particles travel in air?

Answer 19

A few metres

Question 20

How far can gamma rays travel in air?

Answer 20

A few kilometres

Question 21

What can alpha particles be stopped by?

Answer 21

Sheet of paper
Skin

Question 22

What can beta particles be stopped by?

Answer 22

3 mm aluminium foil

Question 23

What can gamma rays be stopped by?

Answer 23

Thick lead

Question 24

What are the sources of background radiation on earth and from space?

Answer 24

• Radon gas
• Ground and buildings
• Food and drink
• Medical
• Nuclear power
• Cosmic rays (from space)

Question 25

What is beta minus decay?

Answer 25

Neutron > proton and electron

Proton stays in nucleus, electron emitted from nucleus at a high speed

Mass number doesn’t change, proton number increases by 1

Question 26

What is beta plus decay?

Answer 26

Proton > neutron and positron

Neutron stays in nucleus, positron is emitted from nucleus at a high speed

Mass number doesn’t change, proton number decreases by 1

Question 27

What are the uses of gamma rays?

Answer 27

• Kill cancer cells (external)
• Sterilise surgical instruments (plastic as they can’t be heated)
• Diagnose cancer (tracer)
• Preserve food (microbes are killed)

Question 28

How do smoke alarms work?

Answer 28

• Alpha particles (often americium-241) ionise the air, causing a current to flow across the gap
• A detector senses the amount of current
• If smoke enters the detector, it will absorb the particles
• The detector will measure a drop in current across the gap
• This will trigger the alarm

Question 29

How are beta particles used to control thickness of paper?

Answer 29

• Beta emitters and detectors are placed either side of the paper
• If the paper is too thick, not as many particles get through
• The detector receives less particles so sends a signal to the rollers to increase force on the paper
• Vice versa if the paper is too thin

Question 30

What are the advantages of irradiation?

Answer 30

• Sterilisation can be done without high temperatures
• It can be used to kill bacteria on things that would melt

Question 31

What are the disadvantages of irradiation?

Answer 31

• It may not kill all bacteria on an object
• Can be harmful – standing where objects are treated could expose cells to damage

Question 32

What are the advantages of contamination?

Answer 32

• Can be used as medical and industrial tracers
• Use of isotopes with a short half life mean exposure can be limited
• Imaging processes can replace some invasive surgical procedures

Question 33

What are the disadvantages of contamination?

Answer 33

• Radioactive isotopes may not go where they are wanted
• Can be difficult to ensure the contamination is fully removed
• Can potentially damage healthy cells

Question 34

What are the advantages of nuclear power?

Answer 34

• Do you not produce carbon dioxide, so no climate change (however construction does)
• Supplies of nuclear fuel will last longer than fossil fuels

Question 35

What are the disadvantages of nuclear power?

Answer 35

• Difficult and expensive to store waste safely
• An accident can spread radioactive material over a large area
• Many people think it is dangerous, so do not want new power stations to be built

Question 36

What is produced in the fission of uranium-235?

Answer 36

• Two daughter nuclei (also radioactive)
• Two or more neutrons
• Energy

Question 37

What is the difficulty with nuclear fusion?

Answer 37

• Nuclei need to get ready close before fusion can happen
• Normally the positive charges on nuclei repel each other (electrostatic repulsion)
• Only at very high temperatures and pressures are the nuclei moving fast enough to overcome this