iGCSE Edexcel Physics > Radioactivity > Flashcards

Radioactivity Flashcards

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1
Q

Describe the plum pudding model of the atom

A

Positively charged sphere with negatively charged electrons embedded in it

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2
Q

Describe Rutherford’s model of an atom

A

Small, dense positively charged nucleus at the center surrounded by orbiting electrons

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3
Q

Describe Rutherford’s experiment

A

Alpha particles were fired at a thin gold foil and some particles were deflected or bounced back

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4
Q

What is the nucleon number (physics)

A

The total number of neutrons and protons

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5
Q

What is the proton number (physics)

A

The number of protons in an atom

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6
Q

Definition of isotope

A

Elements with different numbers of neutrons

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7
Q

What is a stable isotope?

A

Isotopes that don’t undergo radioactive decay

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8
Q

What is a radioactive isotope?

A

An isotope who’s nucleus is unstable and dcays to emit radiation

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9
Q

What is radioactive decay?

A

The spontaneous process where an unstable atomic nucleus loses energy by emitting radiation

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10
Q

What does “Radioactivity is a random process” mean?

A

It is impossible to predict when an individual nucleus will decay but you can make predictions on a much larger scale

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11
Q

What does “Radioactivity is a spontaneous process” mean?

A

You cannot control the process of radioactive decay

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12
Q

What are the 4 types of radioactive decay?

A

Alpha - α
Beta - β
Gamma - γ
Neutron - n

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13
Q

What is a daughter nucleus?

A

The nucleus that results from the radioactive decay of a parent nucleus

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14
Q

What is background radiation?

A

The naturally occuring radiation present in the environment

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15
Q

What are 4 sources of background radiation?

A

Radon gas
Cosmic rays
Rocks
Human activity (nuclear waste etc)

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16
Q

How does nuclear radiation cause ionisation?

A

Radiation knocks electrons out of atoms

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17
Q

Why is a more ionising particle less penetrating?

A

It loses energy faster as it travels so it doesn’t get as far

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18
Q

How can ionising radiation be detected (2 ways)

A

G-M detector
Photographic film

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19
Q

What kind of nucleus is an alpha particle

A

Helium nucleus

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20
Q

What is an alpha particle made up of

A

2 Neutrons
2 Protons

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21
Q

Rank the most penetrating radiation to least

A
  1. Gamma
  2. Beta
  3. Alpha
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22
Q

Rank the most ionising radiaton to least

A
  1. Alpha
  2. Beta
  3. Gamma
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23
Q

Why are alpha particles strongly ionising?

A

They are big, heavy and slow-moving
They collide with lots of atoms and knock lots of electrons out of them

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24
Q

What is the effect of electromagnetic fields on alpha particles?

A

Alpha particles have a positivecharge
They feel electromagnetic forces

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25
What kind of particles are beta particles?
Fast moving electrons
26
How are beta particles emitted?
Emitted from nucleus when (high energy) neutron turns into a proton and electron
27
What is the size and speed of a beta particle?
Quite small Quite fast
28
What is the size and speed of an alpha particle?
Large Slow
29
What is the mass of a gamma ray?
No mass
30
What is the effect of electromagnetic fields on beta particles?
They are negatively charged They feel electromagnetic forces
31
Why are gamma rays very penetrating
They are so small they tend to pass through atoms
32
What is the size and speed of a gamma ray?
No mass Fast
33
When does gamma emission occur?
Always after beta or alpha decay When a nucleus has excess energy Never ALONE
34
What materials block alpha particles
paper skin a few cm of air
35
What materials block beta particles?
thin aluminium
36
What materials block gamma rays?
Thick lead Very thick concrete
37
Why do we measure background radiation?
To work out how much radiation isn't emitted by the source
38
What is an alpha particle in a nuclear equation?
⁴₂He
39
What is a beta particle in a nuclear equation?
⁰₋₁β
40
What is a gamma ray in a nuclear equation?
⁰₀γ
41
What is a neutron in a nuclear equation?
¹₀n
42
What is half-life
The time taken for half of a radioactive substance to decay or its activity to half
43
What is activity (physics)
The rate at which a radioactive source decays
44
How do you measure half-life with a graph?
Measure the time that it takes for activity to half Repeat Average
45
What kind of radiation do medical tracers use? Why?
Beta and Gamma Both will penetrate the skin Both are not harmful in short exposure
46
What kind of half life should a medical tracer have?
Short (a few days) So damage is not caused by over exposure
47
How is radiation used to treat cancer?
Radiotherapy kills cancer cells
48
What type of radiation is used in radiotherapy
Gamma
49
How can food and equipment be sterilised? (radioactivity)
Irradiated with gamma rays
50
How can radiation be used to detect leaks in pipes?
Gamma source flows down pipe Detector above ground It pools where leak is and higher count is detected
51
How is radiation used in thickness control?
Beta source points at paper GM Counter Thicker paper -> lower count Thinner paper -> higher count Rollers adjusted accordingly
52
Why does ionising radiation damage cells?
Radiation collides with molecules in cells Can cause cell mutation or death
53
What is irradiation?
Objects exposed to radioactive radiation
54
What is contamination?
When radioactive particles are transferred to objects they should not be on
55
How can we prevent irradiation?
Lead-lined boxes Protective clothing Long tongs etc
56
How can we prevent contamination?
Tongs Gloves Masks etc
57
What is radioactive waste?
Items that are radioactive or contaminated by radioactive materials that have no further use
58
How can low-level radioactive waste be disposed of?
Burying in landfill
59
How can high-level radioactive waste be disposed of?
Sealed into glass blocks Then sealed into metal canisters Then buried deep underground
60
What is nuclear fission?
The splitting of an atom, which releases energy
61
Is nuclear fission spontaneous?
No - it can be controlled in a nuclear reactor
62
What isotope of uranium is used in a nuclear reactor?
Uranium-235
63
Describe the process of nuclear fission
1. A slow-moving neutron is absorbed by uranium-235 2. Nucleus splits into 2 daughter nuclei and 2/3 fast neutrons 3. Energy is released 4. Chain reaction
64
What is a fissile isotope?
A type of nucleus that can undergo nuclear fission when struck by a neutron
65
Why does nuclear fission produce radioactive waste?
The daughter nuclei of uranium-235 are usually radioactive
66
How does a nuclear reactor work?
Nuclear fission warms gas Steam is produced Turbine is driven
67
What material is the moderator in nuclear reactors?
Heavy water or graphite
68
What is the role of the moderator in nuclear reactors?
To slow down fast-moving neutrons so they can be absorbed by another uranium-235 atom
69
What is the material of fuel rods in nuclear reactors?
Uranium-235
70
What is the material of control rods in nuclear reactors?
Boron or Cadmium
71
What is the role of control rods in nuclear reactors?
They absorb some fast neutrons to control the rate of reaction Can be raised/lowered
72
What radiation is released in fission?
Fast neutrons and gamma rays
73
What is the role of shielding around a nuclear reactor?
To absorb the ionising radiation produced in fission
74
What material is the shielding around a nuclear reactor made of?
Concrete
75
Nuclear fusion definition + where + why important
- fusion = 2 light nuclei join → heavier nucleus + energy - needs extremely high temp/pressure to sustain - hard to reproduce on Earth (conditions hard to achieve/maintain) - stars (incl Sun) use fusion → energy for life on Earth - in most stars: H nuclei fuse → He + lots of energy
76
Where fusion energy comes from + how big it is
- energy from tiny mass → energy conversion - energy released huge - 1 kg H fusion ≈ burning ~10 million kg coal
77
Fusion vs fission (full comparison)
- fusion: nuclei join; small nuclei (H); occurs in stars - fission: nuclei split; large nuclei (U); occurs in reactors - fusion products: larger nuclei (usually stable / not radioactive) + lots energy - fission products: smaller daughter nuclei (usually unstable / radioactive) + lots energy + 2–3 neutrons - fusion needs very high temp/pressure - fission needs thermal neutrons to induce
78
Fusion reactors vs fission reactors (now + future)
- fission reactors common for electricity on Earth - fusion reactors not commercially viable yet; still developing - future fusion likely advantages
79
Advantages of fusion reactors
- more energy per kg than fission - fuel more abundant (H isotopes in water) - no long-lived nuclear waste
80
Disadvantage of fusion reactors
- fusion conditions (temp/pressure) much harder to achieve/maintain than fission
81
Fusion in stars + equilibrium + heavier elements
- stars = huge balls of mostly hydrogen gas - core: H nuclei fuse → He nuclei - example: ²H + ³H → ⁴He + ¹n - ²H (deuterium) + ³H (tritium) = H isotopes; made by other fusion reactions in star - fusion releases huge energy → heat → outward pressure - outward pressure balances gravity → star stable (equilibrium) - in larger stars (hotter), He nuclei can fuse → heavier elements - exam note: know H is star fuel; detailed D–T reaction not required
82
Conditions for fusion + why (electrostatic repulsion)
- fusion only happens if nuclei get extremely close - needs extremely high temp/pressure - reason: protons positive → electrostatic repulsion - high temp → high KE → nuclei move faster → can overcome repulsion - H fusion needs millions °C (usually only star cores) - Earth conditions low temp/pressure → fusion collisions very unlikely - high pressure → high density → nuclei closer → more collisions → more fusion
iGCSE Edexcel Physics
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