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Physics: Uplearn > Nuclear Physics P2 > Flashcards

Nuclear Physics P2 Flashcards

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1
Q

What is ionising radiation?

A

Radiation that can produce positive ions

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2
Q

How strongly ionising is alpha radiation compared to beta radiation?

A

100x

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3
Q

What are three sources of background radiation, including examples?

A
  • Naturally occurring radioactive elements e.g Uranium and Thorium in the ground and Radon in the air.
  • Man-made radioactive substances e.g. medicine and weapons.
  • Cosmic rays which are high energy protons, electrons or nuclei from space.
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4
Q

What is the range in air of alpha and beta radiation?

A

Alpha: Roughly 3-5cm

Beta: About 1m

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5
Q

What is alpha and beta radiation completely absorbed by?

A

Alpha: Paper

Beta: About 5mm of aluminium

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6
Q

For a given source, what is the kinetic energy of alpha and beta particles?

A

Alpha: Constant

Beta: Varies up to a maximum amount

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7
Q

Why can you not see gamma radiation tracks in a cloud chamber?

A

Cloud chambers only show the tracks of charged particles e.g. alpha and beta

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8
Q

What is gamma radiation completely absorbed by?

A

About 10cm of lead

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9
Q

What is the energy of gamma radiation for a given source?

A

Constant

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10
Q

What is gamma radiation’s possible range in air?

A

Infinite

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11
Q

What is the definition of intensity of nuclear radiation?

A

The energy transferred per second per unit area

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12
Q

As a result of radiation ionising atoms in your body, what are two harmful effects?

A

It can damage cells in your body causing radiation burns and it can increase your risk of developing cancer by damaging your DNA

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13
Q

What are the units of radiation dose and how much is a harmful dose?

A

J/kg or Sv, 5Sv is harmful

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14
Q

Name 3 precautions you should take when handling radiation:

A

All sources must be stored in lead-lined containers

Sources must be handled with long tongs or lead lined gloves (Shouldn’t make contact with the skin)

Minimise time spent around radiation by putting it back in the container when not in use

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15
Q

Why is alpha radiation the most suitable radiation for smoke alarms?

A

It is strongly ionising therefore it ionises the air allowing a current to flow and it has poor penetration which allows the smoke to fully block it out and trigger an alarm

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16
Q

Name 3 ways radiation can be useful:

A

Testing thickness of paper/metal, sterilisation and radiotherapy

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17
Q

What is the decay constant?

A

The probability of a nucleus decaying per second

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18
Q

What is the rate of decay?

A

The number of nuclei that decay per second

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19
Q

What is the formula to find the number of atoms?

A

(Mass/Molar Mass) x 6.02 x 10^23

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20
Q

Why does the stability curve on the N-Z graph deviate away from the N=Z line after Z=20?

A

The increased amount of neutrons increases the separation between the protons which therefore decreases the electrostatic force between the nucleons keeping it more stable.

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21
Q

Unstable isotopes to the right of the stability curve on an N-Z graph have a…

A

A higher proton to neutron ratio than the stable isotopes

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22
Q

Unstable isotopes to the left of the stability curve on an N-Z graph have a…

A

A lower proton to neutron ratio than the stable isotopes

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23
Q

What is the half-life of a radioactive isotope?

A

the time it takes for the number of nuclei in a sample to halve

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24
Q

How can carbon dating be used to determine the age of an organism?

A

All living organisms have approximately the same ratio of carbon 14 to carbon 12 but once an organism dies, the carbon 14 begins to decay therefore decreasing the ratio.

This ratio is proportional to the activity of a sample therefore to date it, you compare the dead sample with a living sample.

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25
Q

At the closest approach, what is unique about the potential and kinetic energy?

A

It is the same

26
Q

What are two other applications of radioactive isotopes?

A

Act as tracers to follow the path of a substance through a system e.g. monitoring radiation from iodine injected into a human.

We can use half life calculations to know how long toxic waste must be stored before its activity drops to a safe level.

27
Q

What is argon dating?

A

Newly-formed rocks will only contain potassium-40 however, overtime it undergoes electron capture and produces argon-40. (Or beta minus decay to form calcium-40).

Use nuclei formula to estimate age of rock (solve for t)

28
Q

Why does gamma radiation obey the inverse square law but alpha and beta radiation doesn’t?

A

Gamma is not absorbed unlike alpha and beta which are absorbed in addition to spreading out.

Gamma also spreads uniformly from a point spherically where the area, as to which it spreads, is proportional to the radius squared.

29
Q

What is the deflection of the three types of radiation in a magnetic field?

A

Alpha is deflected, Beta is deflected by a larger amount in the opposite direction and gamma is not deflected at all

30
Q

Why are gamma emitters like Technetium-99 used for medical diagnosis?

A

It is more penetrating than alpha and beta and is weakly ionising so won’t do as much damage.
It also has a short half life so it doesn’t remain in the body long, but long enough for a diagnosis.

31
Q

What range do nuclear radii values lie within?

A

1-10fm

32
Q

What is electron diffraction?

A

High energy electrons are fired at a thin piece of material which are then diffracted by the nuclei.
A detector will measure the intensity of the electrons at each angle of diffraction.

33
Q

What is nuclear density independent of and how can we prove it?

A

It is independent of the nucleon number and the radius and we can prove it by using equations for density, nuclear radius and volume of a sphere.

34
Q

What are the three safety features of a nuclear reactor?

A

Emergency shutdown - all control rods are fully inserted to absorb all neutrons.

Thick steel vessels - the reactor core is housed in a thick steel vessel that can withstand high temperatures and pressures whilst also absorbing beta, gamma and free neutrons.

Concrete Shielding - Entire reactor building is surrounded by thick concrete walls that absorb all excess beta and gamma that escapes the core.

35
Q

What are spent fuel rods and how are they disposed?

A

They are used fuel rods which can no longer sustain a chain reaction.

They are removed and placed in a cooling pond for several years.

After, they are reprocessed at a plant in which they are dissolved in strong chemical baths where fission products are removed and reused.

36
Q

What is done with the rest of the radioactive waste at the reprocessing plant?

A

It is made into a small glass in a process called vitrification.
The vitrified waste is then stored deep underground in geologically stable locations.

37
Q

What are two risks of using nuclear power?

A

Exposure to nuclear radiation from radioactive waste and if the shielding from around the reactor is damaged

38
Q

What are the benefits of using nuclear power?

A

Almost no greenhouse gases are emitted during operation and almost no contribution to air pollution

39
Q

What is the mass defect?

A

The difference between the mass of the nucleus and the nucleons once they have been seperated

40
Q

Why does the mass defect exist?

A

The nucleus is held together by the strong nuclear force therefore work needs to be done to overcome it. This will increase the potential energy and as energy is proportional to mass, so will the mass

41
Q

What is binding energy?

A

The energy required to seperate a nucleus into individual nucleons

42
Q

What relevance does the change in binding energy have?

A

If it is a positive change, the decay will release energy however, if it is negative, it requires energy to be inputted to decay

43
Q

How do you calculate the binding energy per nucleon and what relevance does it have?

A

The higher the energy per nucleon, the more stable it is (Binding Energy/Number of nucleons)

44
Q

In what regions of nucleon number does nuclei undergo fusion and fission reactions?

A

Below 60 = Fusion, Above 60 = Fission

45
Q

How can we conclude that nuclear fusion occurs at really high temperatures?

A

The nuclei must be within the range of the strong nuclear force and for that to happen, they have to overcome the strong electrostatic repulsion. To do this, high speeds are required which suggests that the average kinetic energy will be increased. As average kinetic energy is proportional to temperature, temperature also increases.

46
Q

Why does nuclear fusion only occur within nuclei?

A

At the temperatures required for fusion, matter exists as plasma where electrons are not localised to a particular nucleus

47
Q

What happens during a proton-proton chain?

A
  • 2 Protons fuse together and one undergoes beta plus decay forming a positron, electron neutrino and a Hydrogen 2 nucleus.
  • The Hydrogen 2 nucleus fuses with another proton - creating a Helium 3 nucleus and a gamma ray.
  • Helium 3 nucleus will then form with another Helium 3 nucleus formed the same way and form a Helium 4 nucleus and 2 protons.
48
Q

How can fusion take place on Earth?

A

In reactors such as JET, H2 and H3 isotopes are heated to 150 million Kelvin using electricity and radio waves, forming a Helium 4 nucleus and a neutron.

49
Q

How does a thermal nuclear reactor work?

A

Uranium fuel undergoes fission and transfers energy to the coolant which circulates it around. This will then heat up the water to steam and power turbines to produce electricity.

50
Q

What is induced fission?

A

A uranium nucleus absorbs a free neutron, becomes temporarily unstable and fissions as a result.

51
Q

What is a nuclear chain reaction?

A

As a result of spontaneous fission, the nucleus can release free neutrons. These are then absorbed by other nuclei causing induced fission and a chain reaction.

52
Q

What is the critical mass?

A

The minimum mass of fissile material needed for a chain reaction to occur.

53
Q

Why are the fuel rods made of enriched uranium?

A

In order to increase the mass of uranium 235 concentrated within it to exceed the critical mass.

54
Q

Why are moderators used?

A

Neutrons released from uranium 235 fissions are released too fast to reliably induce fission. These are used to slow the neutrons down by colliding with the atoms in it.

55
Q

What are neutrons that are slowed down called as a result of the moderators?

A

Thermal neutrons

56
Q

How can you minimise the number of collisions needed in the moderator?

A

Nucleon number should be as small as possible

57
Q

What are two common moderators?

A

Graphite and water

58
Q

What are control rods and what can they be made out of?

A

They absorb free neutrons which prevents them from taking part in the chain reaction.
They are made of boron or cadmium which can absorb lots of neutrons without fissioning themselves.

59
Q

What is the critical mass of a fissile material?

A

The minimum mass required to sustain a nuclear chain reaction.

60
Q

What is meant by nuclear fusion?

A

The joining together of two nuclei to form one large nucleus

Physics: Uplearn (10 decks)

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