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Physics 🧲 > Radioactivity > Flashcards

Radioactivity Flashcards

1
Q

What is the activity of a radioactive source?

A

The number of atoms that decay every second

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2
Q

What is the unit for activity?

A

Becquerel (Bq)

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3
Q

What is the half life of a radioactive isotope?

A

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

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4
Q

Why is ionising radiation dangerous?

A

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

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5
Q

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

A
  • 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
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6
Q

What are medical tracers?

A

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

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7
Q

How are medical tracers used?

A

- 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

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8
Q

How do PET scanners work?

A
  • 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
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9
Q

How are tumours treated internally?

A
  • A radioactive source is injected or eaten/drunk by the patient
  • It then targets the tumour without affecting the cells around it too much
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10
Q

How are tumours treated externally?

A
  • 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
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11
Q

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

A
  • 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
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12
Q

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

A
  • It slows down the neutrons so that fission can occur
  • It is often graphite or water
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13
Q

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

A
  • They absorb excess neutrons
  • Lowering a control rod reduces fission reactions as they will absorb more neutrons
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14
Q

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

A

Concrete shielding

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15
Q

How big is a typical atom?

A

10^-10m

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16
Q

How big is a typical molecule?

A

10^-9m

17
Q

How big is the diameter of a typical nucleus?

A

10^-15m

18
Q

How far can alpha particles travel in air?

A

Less than 5 cm

19
Q

How far can beta particles travel in air?

A

A few metres

20
Q

How far can gamma rays travel in air?

A

A few kilometres

21
Q

What can alpha particles be stopped by?

A

Sheet of paper
Skin

22
Q

What can beta particles be stopped by?

A

3 mm aluminium foil

23
Q

What can gamma rays be stopped by?

A

Thick lead

24
Q

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

A
  • Radon gas
  • Ground and buildings
  • Food and drink
  • Medical
  • Nuclear power
  • Cosmic rays (from space)
25
Q

What is beta minus decay?

A

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

26
Q

What is beta plus decay?

A

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

27
Q

What are the uses of gamma rays?

A
  • Kill cancer cells (external)
  • Sterilise surgical instruments (plastic as they can’t be heated)
  • Diagnose cancer (tracer)
  • Preserve food (microbes are killed)
28
Q

How do smoke alarms work?

A
  • 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
29
Q

How are beta particles used to control thickness of paper?

A
  • 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
30
Q

What are the advantages of irradiation?

A
  • Sterilisation can be done without high temperatures
  • It can be used to kill bacteria on things that would melt
31
Q

What are the disadvantages of irradiation?

A
  • It may not kill all bacteria on an object
  • Can be harmful – standing where objects are treated could expose cells to damage
32
Q

What are the advantages of contamination?

A
  • 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
33
Q

What are the disadvantages of contamination?

A
  • Radioactive isotopes may not go where they are wanted
  • Can be difficult to ensure the contamination is fully removed
  • Can potentially damage healthy cells
34
Q

What are the advantages of nuclear power?

A
  • Do you not produce carbon dioxide, so no climate change (however construction does)
  • Supplies of nuclear fuel will last longer than fossil fuels
35
Q

What are the disadvantages of nuclear power?

A
  • 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
36
Q

What is produced in the fission of uranium-235?

A
  • Two daughter nuclei (also radioactive)
  • Two or more neutrons
  • Energy
37
Q

What is the difficulty with nuclear fusion?

A
  • 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

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