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Science > Radioactivity > Flashcards

Radioactivity Flashcards

1
Q

What is the particle theory?

A

Model that helps explain the properties of solids, liquids and gases, with atoms represented as spheres

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2
Q

When do chemical reactions occur?

A

When different atoms in substances become joined in different ways

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3
Q

What are alpha particles?

A

Positively charged subatomic particles with 2 protons and 2 neutrons (like a helium atom), relative mass of 4 and a charge of +2

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4
Q

What experiment suggested that atoms were mostly empty space with most of their mass concentrated in a tiny nucleus?

A

Ernest Rutherford’s gold foil experiment

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5
Q

What are nucleons?

A

Protons and neutrons

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6
Q

What are the relative charges and mass of each subatomic particle?

A
  • Proton = +1, 1
  • Neutron = 0, 1
  • Electron = -1, 1/2000
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7
Q

What is an isotope?

A

Atoms of a single element with a different number of neutrons

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8
Q

What do isotopes of the same element have the same and different of?

A

The same atomic number, but a different mass number

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9
Q

What is the name of the certain orbits that electrons in an atom exist in?

A

Electron shells

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10
Q

Each electron shell at a different what?

A

Energy level

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11
Q

What is an emission spectrum?

A

When each colour is a different wavelength of light (different for each element)

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12
Q

What is an ion?

A

A stable atom - an atom that has lost or gained electrons to obtain a full outer shell

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13
Q

What is ionising radiation?

A

Radiation that causes electrons to escape

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14
Q

What is background radiation?

A

Exposure to low-level ionising radiation from space and natural radioactive substances in the environment

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15
Q

What is radon gas produced by?

A

Rocks that contain small amounts of uranium

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16
Q

Name some contributing factors to background radiation

A
  • Food that naturally contain small amounts of radioactive substances
  • Hospital treatments like X-rays, gamma-ray scans and cancer treatments
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17
Q

What are cosmic rays?

A

High-energy, charged particles that stream out of the Sun and other stars

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18
Q

How can radioactivity in the workplace be measured?

A

Using dosimeters - contains photographic film that once developed, the darker colour shows the more radiation exposure (the dose), with newer ones with materials that change colour without needing to be developed

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19
Q

How does a Geiger-Muller (GM) tube measure the radioactivity of a source?

A

Radiation passing through the tube ionises gas inside it and allows a short pulse of current to flow; once connected to a counter, pulses are counted and GM tube may give click each time radiation is detected. Count rate is given (number of clicks per second/minute)

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20
Q

What does it mean if the nucleus of a radioactive substance is unstable?

A

It can easily change or decay

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21
Q

What happens when decay occurs?

A

Radiation is emitted which causes the nucleus to lose energy and become more stable

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22
Q

Why can you not predict when a nucleus will decay?

A

It is a random process

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23
Q

What are beta particles?

A

High-energy, high-speed electrons with a relative mass of 1/1835 and a charge of -1

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24
Q

What are positrons?

A

High-energy, high-speed particles with the same mass as electrons but a charge of +1

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25
Q

What are gamma rays?

A

High-frequency EM waves that travel at the speed of light, with no electric charge

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26
Q

What does penetrate mean?

A

Pass through

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27
Q

Describe the penetration of alpha particles

A
  • Will travel a few cm in air
  • Very ionising
  • Can be stopped by a sheet of paper
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28
Q

Describe the penetration of beta particles

A
  • Will travel a few m in air
  • Moderately ionising
  • Can be stopped by 3mm thick aluminium
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29
Q

Describe the penetration of gamma rays

A
  • Will travel a few km in air
  • Weakly ionising
  • Need thick lead/several m of concrete to stop them
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30
Q

Why do alpha particles have a short penetration distance?

A

Due to being emitted at high speeds and their high relative mass, they transfer a lot of energy and are good at ionising atoms they encounter. However, each time they ionise an atom, they lose energy and so have a short penetration distance

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31
Q

What happens during beta decay?

A

A neutron changes into a proton and an electron, and the electron is ejected from the atom and so the atomic number decreases by 1 but no change to mass number

32
Q

What happens during positron decay?

A

A proton becomes a neutron and a positron, and so the atomic number decreases by 1 but the mass number does not change

33
Q

What is the activity of a radioactive substance?

A

The number of nuclear decays per second

34
Q

What is the activity of a radioactive substance measured in?

A

Becquerels (Bq) - one becquerel is one nuclear decay each second

35
Q

What is half-life?

A

The time taken for half the unstable nuclei in a sample of a radioactive isotope to decay

36
Q

How can food be irradiated?

A

With gamma rays to kill bacteria

37
Q

How can surgical instruments be sterilised to kill microorganisms?

A
  • Usual method = heat them
  • Some instruments cannot be heated, so are sealed into bags and irradiated with gamma rays, which can penetrate the bag and the equipment
38
Q

How can radioactive isotopes be used as tracers?

A
  • Gamma source added to water is used to detect leaks in underground water pipes
  • When there’s a leak, water flows into the surrounding earth
  • A GM tube following the path of the pipe will detect higher levels of radiation where there is a leak
39
Q

How are alpha particles used in smoke alarms?

A
  • Alarm contains source of alpha particles, usually americiium-241
  • Detector has electrical circuit with air gap between 2 electrically charged plates
  • Americium-241 source releases the alpha particles which ionise molecules in the air
  • Ions are attracted to plates with opposite charge and so allow small electrical current to flow
  • As long as current flowing, alarm will not sound
  • When smoke gets into air gap, smoke particles slow down ion so current flowing across gap decreases
  • Alarm sounds when current drops below certain level
40
Q

What is a mutation?

A

When small amounts of radiation over long periods of time can damage the DNA inside a cell

41
Q

How can a mutation cause cancer?

A

DNA contains instructions controlling a cell, so mutation can cause cell to malfunction and may cause cancer

42
Q

How can mutations be passed onto next generation?

A

If there a gene mutation in the gametes

43
Q

What precautions can be taken to minimise risks from radiation if working with radioactive materials?

A
  • Increase distance from source by using tongs instead of only gloved hands
  • Not pointing sources at people
  • Storing them in lead-lined containers
  • Shielding the source
  • Minimise time spent with presence of source
  • Use dosimeter to closely monitor exposure
44
Q

When are patients exposed to radiation?

A

For treatment - when the benefits are greater than the possible harm

45
Q

What precautions are taken for patients treated with radiation?

A
  • Minimum dose

- Sources with short half-lives to minimum exposure time

46
Q

What happens when someone is irradiated?

A

When they exposed to alpha, beta or gamma radiation from nearby radioactive materials (when move away, irradiation stops)

47
Q

What happens when someone becomes contaminated with radiation?

A

If they get particles of radioactive material on their skin or inside their body (will continue until material decays or source of contamination is removed)

48
Q

Where are radioactive tracers often injected?

A

Into the bloodstream, but can be swallowed, inhaled or injected directly into an organ

49
Q

How is the location of a radioactive tracer found?

A

Using one or more gamma cameras

50
Q

How can gamma cameras be used to detect tumours?

A

The tracer is made using radioactive glucose molecules because very active cells like cancer cells take up glucose more quickly than others

51
Q

How can tracers be used to find source of internal bleeding?

A

The tracer is injected into the blood and the gamma cameras detect the area of highest gamma radiation, which is where the bleeding is occurring

52
Q

How do tracers that emit positrons work?

A
  • Tracer emits positron
  • When positron meets electron, both it and electron are destroyed and 2 gamma rays are emitted in opposite directions
  • Detector in a PET scanner moves around the patient, building up set of images where different amounts of gamma radiation are coming from
53
Q

Why must radioactive isotopes used as medical tracers be made close to the hospital?

A

They need to have short half-lives so that other parts of the patient’s body are affected as little as possible, meaning they lose their reactivity quickly

54
Q

What are the 2 types of nuclear reaction that are used as a source of energy on a large scale?

A

Nuclear fission and nuclear fusion

55
Q

What happens in nuclear fission?

A

Large nuclei (such as uranium-235) break up to form smaller nuclei and release energy. These reactions are used in power stations

56
Q

What happens in nuclear fusion?

A

Two small nuclei join together (fuse) to form a larger nucleus. Fusion reactions release energy inside the Sun

57
Q

What is special about nuclear fuels?

A

They store a lot more energy per kg than any other type of fuel, making them useful for naval ships and submarines

58
Q

Do nuclear fuels burn?

A

No, so they don’t need air to allow them to release energy and do not produce CO2

59
Q

What do conventional power stations that burn fossil fuels produce?

A

CO2, soot and acidic gases

60
Q

What do nuclear power stations produce?

A

Waste that will stay radioactive for millions of years, which is expensive to treat as it needs to be sealed into concrete or glass and buried safely

61
Q

What does decommission mean?

A

Dismantle safely

62
Q

What happens when a uranium-235 nucleus absorbs a neutron?

A
  • It immediately splits into 2 smaller daughter nuclei, which are also radioactive
  • 2 or more neutrons are released
  • Both daughter nuclei and the neutrons store a lit of KE because they are moving at high speeds
  • Energy is also transferred from the fission by heating
63
Q

What creates an uncontrolled nuclear chain reaction in nuclear fission, such as occurs in an atomic bomb?

A

If the neutrons released are absorbed by other uranium-235 nuclei, these will become unstable and release more neutrons when their nuclei split. These will be absorbed by yet more uranium nuclei which in turn split up, releasing more neutrons

64
Q

What are fuel rods?

A

Where the fuel in a nuclear reactor is stored

65
Q

What happens inside a reactor core?

A

Fuel rods are inserted into holes in a material called a moderator, which slows down the neutrons

66
Q

What is done to increase the chance that the neutrons will be absorbed by another uranium-235 nucleus?

A

Neutrons leave the fuel rods at high speeds which are slowed down

67
Q

How is the chain reaction in a nuclear reactor controlled?

A

Using control rods, which contain elements that absorb neutrons

68
Q

Where are control rods placed in a nuclear reactor?

A

Between the fuel rods

69
Q

How is electricity generated from a reactor core?

A
  • Energy released from the core is transferred to a coolant, which is pumped through the reactor (coolant can be water, gas or liquid metal)
  • Hot coolant is pumped to a heat exchanger where it is used to make steam
  • Steam drives a turbine, which turns a generator to produce electricity
70
Q

What has happened to the lost mass in nuclear fusion?

A

It has been converted to energy

71
Q

What is the main energy source for stars?

A

Fusion reactions in which hydrogen nuclei combine to form helium

72
Q

What is electrostatic repulsion?

A

The result of interaction between sources of the same charge, forcing them to repel

73
Q

What does the strong gravitational field of the Sun create?

A

Extremely high pressures at its centre (forcing nuclei to be very close to each other, so are more likely to collide)

74
Q

When can some nuclei overcome their electrostatic repulsion and fuse?

A
  • When are travelling at high temperatures (increases KE and move faster)
  • Close enough due to high central pressures
75
Q

Which reactor theoretically produce more energy: fusion or fission?

A

Fusion reactors

76
Q

Which reactor produces fewer problems with safely disposing of radioactive waste materials?

A

Fusion reactors

77
Q

What is a problem with fusion experimental reactors?

A

It is very difficult and expensive to sustain the extreme temperatures and pressures (conditions) required for fusion; and so far none of the reactors have produced more energy than has been put in, so fusion power is a long way off

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