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Physics > 12 - Nuclear Physics > Flashcards

12 - Nuclear Physics Flashcards

1
Q

Describe the Rutherford scattering experiment.

A
  • a beam of alpha particles was directed at a thin gold foil.
  • occurs in a vacuum so that no collision between air particles and alpha particles can occur.
  • the experiment was done in order to determine the structure of an atom.
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2
Q

In the Rutherford scattering experiment it was observed that most of the alpha particles passed straight through. What can we infer from that?

A
  • that most of the atom is made up of empty space
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3
Q

What evidence was there that suggested that the nucleus had a positive charge?

A
  • nucleus repels the alpha particles and caused it to deflect from it original path, some of them even bounced back
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4
Q

Name 3 types of radiation?

A
  • Alpha
  • Beta (plus and minus)
  • Gamma
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5
Q

Order Alpha, Gamma and Beta radiation starting with the most ionising?

A
  • Alpha
  • Beta
  • Gamma
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6
Q

Order Alpha, Gamma and Beta radiation starting with the most penetrating?

A
  • Gamma
  • Beta
  • Alpha
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7
Q

A sheet of paper can block which type of radiation?

A
  • alpha
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8
Q

This equation represents which process?

A
  • electron capture
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9
Q

When a nucleus decays through gamma radiation, how does the atomic number and mass number change?

A
  • they remain the same
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10
Q

Why is ionising radiation seen as dangerous?

A
  • because it can kill or mutate cells, which could lead to mutations and lead to things such as cancer
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11
Q

Which radiation is more harmful inside a human body, alpha or gamma?

A
  • alpha radiation
  • because it has a higher ionising power so it would damage more cells.
  • It is also very poorly penetrating, therefore it is not able to leave the body, whereas gamma radiation is highly penetrating.
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12
Q

Give an example of a real life use of Beta decay and explain why Beta is chosen for this.

A
  • Beta radiation can be used to measure the thickness of paper or aluminium foil.
  • Alpha isn’t used as it is less penetrative and wouldn’t reach the detector on the other side.
  • Gamma radiation is too penetrative and would pass through everything.
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13
Q

Which type of radiation follow inverse square law?

A
  • Gamma
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14
Q

What does the inverse square law state?

A
  • the intensity is inversely proportional to the square of the distance from the source.
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15
Q

What is intensity measure in?

A
  • measured in watts per square meter (W/m²)
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16
Q

Describe an experiment which can be used to show the inverse square law of gamma rays.

A
  • Firstly measure background radiation (using geiger counter), without the gamma source in the room
  • The put the gamma source at a set distance (1m) from the gieger counter and measure the count rate per minute. Record 3 measurements for each distance and take an average
  • repeat this for many distances going up in 10 cm intervals
  • Take away the background radiation from each reading
  • square each of the distances
  • plot a graph of the count rate per minute against 1 over distance squared
  • if it is a straight line through the origin then it confirms they are directly proportional
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17
Q

What is background radiation?

A
  • Radiation that is constantly in the surroundings from sources such as rocks and cosmic rays
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18
Q

What is the decay constant?

A
  • the probability of a nucleus decaying per second
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19
Q

What are the unites for the decay constant?

A
  • s‾¹
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20
Q

What is half life?

A
  • the time it takes for half of the unstable nuclei in a substance to decay
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21
Q

What equation can you use to work out the half life of an object?

A
  • T½ = ln(2)/λ
22
Q

Complete the equation. λN = ?

A
  • A (activity)
23
Q

What is activity measured in?

A
  • Bq (decays per second)
24
Q

True or false. Radioactive isotopes decay exponentially.

A
  • True
25
Q

Why is Technetium 99m useful in medicine?

A
  • because it releases gamma radiation
  • it has a short half life therefore it doesn’t stay highly radioactive for long
  • half life of 6 hours: long enough to be detected
  • it can also be made near to the hospital
  • easy to detect outside the patient
26
Q

What does the graph of N against Z show?

A
  • shows the relationship between proton number and neutron number. The graph shows a stability curve which starts as N=Z until N value of 20.
  • after that the graph curves upwards and becomes steeper
27
Q

Where on the curve does B- decay occur and why?

A
  • above the stability line, because the nuclei found there contains too many neutrons.
  • therefore when beta minus decay occurs the neutron turns into a proton and it becomes more stable
28
Q

What type of decay occurs below the stability line and why?

A
  • beta plus decay. As the isotopes found here often have too many protons.
  • therefore when beta plus decay occurs the protons turns into a neutron and it becomes more stable
29
Q

How does the heavier nuclei often decay?

A
  • through alpha decay
  • this is because alpha decay emits a helium nucleus therefore causing the nuclei to become less heavy and more stable
30
Q

A alpha particle is fired at a nucleus, with the kinetic energy at the start known. How can you use energy conservation to find closest approach of particle?

A
  • we know the kinetic energy it moves with towards the nucleus and the electrostatic potential energy that repels it. These are equal to each other. therefore Ek = Eelec
31
Q

How is electron diffraction is used to determine nuclear radius?

A
  • an electron beam is fired at a thin sheet of the desired atom
  • a diffraction pattern is produced on a screen behind
  • using the angle of a minimum we can use equations to calculate radius
32
Q

What is the relationship between nuclear radius and nucleon number?

A
  • therefore nuclear radius is directly proportional to the cube root of the nucleon number
33
Q

True or false. The density of a nucleus is independent of its radius.

A
  • True
34
Q

What equation is used to convert mass to its energy equivalent?

A
  • E = mc²
35
Q

What is the mass defect?

A
  • the difference between the total mass of all the nucleons separately compared to the mass of the nucleus
36
Q

Why is there a mass defect?

A
  • because energy is needed to bring the constituent parts of a nucleus together
  • therefore the mass equivalent of the energy is lost and the total mass decreases
37
Q

What is binding energy?

A
  • the energy required to separate a nucleus into its constituent parts
38
Q

What is nuclear fission?

A
  • where a unstable nuclei splits into 2 smaller nuclei
  • often occurs with the larger nuclei
  • the binding energy per nucleon increases when fission occurs therefore the overall process releases energy
39
Q

What is fusion?

A
  • when two small nuclei fuse together to create a larger nuclei
  • the new nucleus has a larger binding energy per nucleon than the old nucleus, therefore energy is released in the process
40
Q

Why is it difficult to make fusion occur on earth?

A
  • there is a large repulsion between the two positively charged nuclei, therefore a lot of energy is required to overcome the repulsion and fuse them together
  • it is hard to get a material that can withstand the heat and be cost effective
41
Q
  • How is fission used in nuclear reactors?
A
  • rods of Uranium-235 absorb neutrons and become unstable and then split into two daughter nuclei.
  • it also releases 2/3 more “thermal” neutrons that go on to be reabsorbed by another uranium-235 nucleus, producing a chain reaction
42
Q

What is the purpose of a moderator?

A
  • to slow down the “thermal” neutron so they travel slow enough to be absorbed by the uranium
  • they do this through elastic collisions between the nuclei of the moderator atoms and the thermal neutrons
43
Q

Why are control rods essential for nuclear power stations?

A
  • they stop the chain reaction from being out of control
  • they absorb neutrons in order to control the chain reaction
  • height of them can be adjusted to control rate at which fission occurs
44
Q

Is boron used as a control rod or a moderator?

A
  • control rod
45
Q

Give an example of a substance that can be used as a moderator?

A
  • water
46
Q

What is the purpose of using water as a coolant?

A
  • it allows heat from the nuclear reactor to escape which stops the reactor from overheating.
47
Q

What is the critical mass?

A
  • the minimum mass of fuel needed for a chain reaction to occur
48
Q

Which waste products from a nuclear reactor cause the highest risk?

A
  • spent fuel rods
49
Q

How is high-level waste disposed of?

A
  • they are first stored in cooling ponds
  • waste is then encased in glass (vitrified) and placed in thick steel casks and stored in deep caverns
50
Q

What is low level waste contained in?

A
  • they are sealed in containers and put underground until it is safe again
51
Q

What are the risks and benefits of nuclear power stations?

A

Benefits:
- no polluting gasses
- need far less fuel then conventional power stations
- reliable
Risks:
- produce radioactive waste
- possibility of nuclear meltdown

Physics (16 decks)

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