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Physics > Topic 6 - Radioactivity > Flashcards

Topic 6 - Radioactivity Flashcards

1
Q

What is the overall size of atoms?

A

1 * 10^(-10) metres

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2
Q

What happens to unstable isotopes?

A

They tend to decay into other elements and give out radiation in order to try to become more stable (radioactive decay)

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3
Q

What is the charge and mass of a positron?

A 
Charge = +1
Mass = 0.0005
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4
Q

What happens when an electron absorbs electromagnetic radiation with the right amount of energy (alot of energy)?

A
  1. The electron moves up an energy level but quickly falls back down to its original energy level
  2. The electron will emit the same amount of energy it absorbed and the energy is carried away by EM radiation
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5
Q

High energy when electrons move up energy levels means higher f…..

A

frequency

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6
Q

Why does the frequency of generated radiation decrease as you move further away from the nucleus?

A
  • As you move further away from the nucleus, the shells become closer together so less energy is needed to move the electrons to a higher energy level
  • low energy = low frequency (of radiation)
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7
Q

What happens when an atom loses an electron?

A

It is said to be ‘ionised’ and turns into a positive ion

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8
Q

Outline the 3 types of ionising radiation

A
  1. Alpha radiation
  2. Beta radiation
  3. Gamma radiation
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9
Q

What are alpha particles?

A
  • Helium nuclei (4, 2)
  • They dont penetrate far into materials (they only travel a few cm in air and are absorbed by a thin sheet of paper
  • They are strongly ionising (because of their size)
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10
Q

What are beta-particles?

A
  • fast moving electrons/positrons (electrons positive charge)
  • Beta-minus particles have a range in air of a few metres and are absorbed by a sheet of aluminium
  • Positrons have a smaller range as when it meets an electron, the two destroy each other and produce gamma rays - annihilation
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11
Q

What are gamma rays (short wavelength)?

A
  • waves of EM radiation that carry away energy from a declayed nucleus
  • They penetrate far into materials and air
  • Weakly ionising (they tend to pass through materials rather than collide with them)
  • They can be absorbed by thick sheets of lead/concrete
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12
Q

What happens to the mass/atomic number in alpha decay

A
  • The mass number decreases by 4

- The atomic number decreases by 2

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13
Q

What happens to the mass/atomic number in beta-minus decay?

A
  • The mass number doesnt change

- The atomic number increases by 1

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14
Q

What happens to the mass/atomic number in positron emission?

A
  • The mass number doesnt change

- The atomic number decreases by 1

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15
Q

What happens to the mass/atomic number in neutron emission?

A
  • The mass number decreases by 1

- The atomic number stays the same

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16
Q

Radioactivity is a totally …….. process

A

random

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17
Q

what is 1 Bq equal to?

A

1 decay per second

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18
Q

How does a geiger-Muller tube work?

A

It clicks each time it detects radiation . The tube can be attacked to a counter, which displays the number of clicks per second

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19
Q

How does photographic film work?

A

The more radiation the films exposed to, the darker it becomes

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20
Q

Define half-life?

A

The half-life is the average time taken for the number of radioactive nuclei in an isotope to halve

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21
Q

What does a short-half life mean?

A
  • radioactive activity falls quickly, because the nuclei are very unstable and rapidly decay
  • they’re dangerous at the start as they emit a high level of radiation they emit but they quickly come safe
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22
Q

What does a long-half life mean?

A
  • Activity falls more slowly because most of the nuclei dont decay for a long time
  • They’re dangerous as nearby areas are exposed to radiation for millions of years
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23
Q

How do you work out the half life of a sample?

A
  1. Count how many half lives it took for a samples radioactive activity to fall to e.g. 40 bq
  2. Divide the number of half lives, by the full time taken for radioactive sample to fall to 40 (time is given in question)
24
Q

How do you work out the half life on a activity-time graph

A

you find the time that corresponds with the half life on the graph

25
Q

Where can background radiation come from?

A
  1. unstable isotopes that are all around us e.g in the air, foods, building materials and rocks
  2. From Space (cosmic rays)
  3. From human activity e.g. fallouts from nuclear explosions and nuclear waste
26
Q

Define absorbed radiation dose?

A

The amount of radiation were exposed to

27
Q

What happens to nuclei that have undergone radioactive decay (in terms of arrangement and gamma rays)?

A

They undergo nuclear arrangement and releases energy as gamma radiation

28
Q

What does half-life enable us to predict?

A

Half-life enables us to predict the activity of a very large
number of nuclei during the decay process

29
Q

Describe how house alarms use alpha radiation?

A

1- A weak source of alpha radiation is placed in a smoke detector, close to two electrodes
2- The source causes ionisation and a current flows
3- In a fire, smoke will absorb the radiation - the current stops and an alarm sounds

30
Q

Food and equipment can be sterilised using…

A

a high dose of gamma rays with a long half life

31
Q

How is radiation used in tracers?

A

1- tracers ( radioactive isotopes - must be gamma or beta and have a short half life) are injected into a patients body and its progress around the body is followed using an external detector
2- can be used to detect and diagnose medical conditions e.g cancer

32
Q

How is radiation used in thickness gauges?

A
  • You direct BETA radiation through the stuff being made e.g. paper and put a detector on the opposite side.
  • paper must be connected to a control unit
  • When the amount of detected radiation changes, paper is too thick/thin so the control unit adjusts the thickness
33
Q

Why must beta radiation be used in thickness gauges?

A

Because with beta, the paper will partly block the radiation

34
Q

How can ionisation lead to tissue damage?

A

Radiation can enter living cells and ionise atoms and molecules within them

35
Q

How can lower does and higher does of radiation affect cells?

A

Lower doses - they cause minor damage to cells, which could give rise to mutant cells (cancer)

Higher doses - they kills cells completely, which can cause radiation sickness (vomiting, tiredness, hair loss)

36
Q

Which types of radiation are the most dangerous outside the body and inside the body?

A

Outside the body - beta and gamma as they can penetrate the skin

Inside the body - alpha as they’re strongly ionising

37
Q

How can we reduce the effects of the dangers of ionising radiation? (dont include half life)

A

1- inject alpha emitters right next to a tumour to avoid other cells being damaged
2- Use shielding (keep radioactive machines in a deignated room to reduce risk to staff and patients in hospital)

38
Q

Which is more dangerous - long half life or short half life?

A

Long half life as the activity falls more slowly

39
Q

What precaution must be taken when choosing radioactive sources (relate to half life)

A

Find a source that has the right evel of activity, for the right amount of time and that isnt too dangerous for too long

40
Q

What is:

  • irradiation ?
  • contamination?

and describe the effects of contamination

A

Irradiation :
- being exposed to radiation (doesnt mean that something is radioactive)

Contamination:

  • when unwanted radioactive atoms get onto an object
  • contaminating atoms might decay, releasing radation which can cause you harm
  • radioactive particles could get inside your body
41
Q

How can we reduce the effects of irradiation?

A
  • keep sources in lead-lined boxes,
  • standing behind barriers
  • being in a different room
  • using remote controlled arms
  • staff can wear photographic film badges to monitor their exposure
42
Q

How can we reduce the effects of contamination?

A
  • gloves and tongs should be used

- wearing protective suits to prevent inhaling radioactive particles

43
Q

How are beta emitters (in implants) used in internal radiation therapy?

A

They’re used in implants, near a tumour and they can penetrate the casing of the implants to damage cancerous cells
- as they have a longer range, they can do damage to normal healthy cells

44
Q

The half lives of the sources used in internal radiation therapy is usually …… whilst the half lives of sources used in external radiation therapy is quite ….. (so they dont have to be replaced often

A
  1. Short

2. long

45
Q

How are tumours treated externally?

A

Gamma rays is aimed at the tumour (they can penetrate through the body) but even if shielding is placed on other areas of the patients body, damage can still be done to healthy cells

46
Q

How does PET scanning work?

A
  1. Patient is injected with a substance used by the body, e.g. glucose, containing a radioactive isotope with a short half life to act as a tracer
  2. When positrons meet electrons in an organ, they annihilate to emit high-energy gamma rays in opposite directions. (Detectors outside body detect pair of gamma rays - tumour will lie along same path as pair)
  3. By detecting at least 3 pairs, location of tumour can be found using triangulation
47
Q

In PET scanning, what does the distribution of radioactivity match up with and why?

A

It matches up with metabolic activity as more of the radioactive substance (e.g. glucose), injected into the patient, is taken up and used by cells that are doing more work

48
Q

Why do some hospitals have their own cyclotron to make the isotopes on site?

A
  • Because the isotopes have short half lives
  • if the isotopes had to be transported over large distances, their activity could be too low by the time they arrive in the hospital
49
Q

What are the pros and cons of using nuclear power to generate electricity

A

Pros:

  • doesnt release CO2 or sulfur dioxide
  • very reliable source of energy
  • huge amount of energy can be generated from a small amount of nuclear material

Cons:

  • risk of explosions/leaks in land or rivers
  • Public view it as dangerous
  • Cant be disposed of safely as they have long half lives
  • cost is expensive
50
Q

nuclear reactions, such as

  • …….
  • ……
  • ……..

can be a source of energy

A
  1. radioactive decay
  2. nuclear fusion
  3. nuclear fission
51
Q

Describe the fission of uranium - 235

A
  1. A slow moving neutron is fired at a large unstable nucleus (U-235) and the neutron is absorbed by the nucleus to make the atom more unstable so that it splits
  2. When U-235 splits, it forms 2 lighter daughter nuclei and energy is released
  3. The u-235 can split into lots of different pairs of atoms (e.g. krypton and barium) but all these new nuclei are radioactive
  4. this cycle repeats to create a chain reaction
52
Q

How are chain reactions in reactors carefully controlled?

A

1- fast moving neutrons are slowed down by placing uranium fuel rods in a moderator so that the uranium can capture the neutrons
2- Control rods, that are placed in between the fuel rods, limit the rate of fission by absorbing excess neutrons
3. This creates a steady rate of nuclear fission to reduce the risk of an explosion

53
Q

Describe how nuclear power stations generate electricity?

A
  1. The energy released by fission is transferred to thermal energy of moderator
  2. This is then tranferred to the thermal energy store of the water (coolant) in the boiler, which causes the water to boil and energy to be transferred to the kinetic energy store of the steam
  3. Energy is then tranferred to the kinetic energy store of the turbine and hence, the kinetic energy store of the generator to generate electricity
54
Q

Whst is nuclear fusion?

A

when two light nuclei collide at high speed to create a larger, heavier nucleus. The heavier nucleus does not have as much mass as the two separate nuclei as some of the mass is converted to energy and released as radiation

55
Q

Fusion only happens at …………………………………………….

and explain why?

A
  • high temperatures and pressures
  • the positivitely charged nuclei have to get very close to fuse, so the stong force due to electrostatic repulsion has to be overcome
56
Q

Why is nuclear fusion so difficult to do?

A

No material can withstand that kind of temperature, it would just be vaporised and therefore, fusion reactors are really hard and expensive to try to build

Physics (13 decks)

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