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Physics > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

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1
Q

Describe the Rutherford Scatteing experiment

A

● Beam of alpha particles directed at thin gold foil
● Occurred in a vacuum so no collisions between air particles and alpha particles
● Was done to determine 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

Most of the atom consists of empty space

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3
Q

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

A

Because it caused some of the positive alpha particles to be repelled/deflected (like-charges repel)

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4
Q

Name 3 types of radiation

A

Alpha, Beta, Gamma

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5
Q

Order Alpha, Gamma and Beta radiation in order of ionising power, starting with the most ionising

A

Alpha, Beta, Gamma

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6
Q

Order Alpha, Gamma and Beta radiation in order of penetration power, 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

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

A

They remain the same as the number of protons and neutrons doesn’t change

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9
Q

Why is ionising radiation seen as dangerous?

A

Because it can kill or mutate cells, leading to things such as cancer

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10
Q

Which radiation is more harmful inside a human body, Alpha or Gamma?

A

Alpha

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11
Q

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

A

Measuring paper thickness - Alpha is not penetrative enough and Gamma is too penetrative

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12
Q

Which type of radiation follows the inverse square law?

A

Gamma

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13
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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14
Q

What is intensity measured in?

A

W/m²

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15
Q

What is background radiation?

A

Radiation that is constantly in the surroundings from sources such as rocks and food

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16
Q

What is the decay constant (λ)?

A

The probability of a nucleus decaying per second

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17
Q

What are the units for the decay constant (λ)?

A

S‐¹

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18
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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19
Q

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

A

T½ = ln(2)/λ

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20
Q

Complete the equation, λN = ?

A

Activity

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21
Q

What is activity measured in?

A

Becquerels (decays per second)

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22
Q

True or False: Radioactive isotopes decay exponentially?

A

True

23
Q

Why is Technetium-99 useful in medicine?

A

Gamma radiation has a short half life, so it doesn’t stay radioactive for long, and is easy to detect outside patient.

24
Q

What does the graph of N against Z show?

A

The relationship between Proton number and Neutron number

25
Q

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

A

Above the stability line - nuclei contain too many neutrons

26
Q

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

A

β+ as these nuclei contain too many protons

27
Q

How does the heavier nuclei often decay?

A

Alpha decay

28
Q

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

A

At this point, the KE and PE are equal, so we can rearrange for distance (r)

29
Q

How is electron diffraction used to determine the diameter of a radius?

A

● Electron beam fired at thin sheet
● Diffraction pattern produced on screen behind
● Calculate diameter using angle of a minimum

30
Q

What is the relationship between nuclear radius (R) and nucleon number (A)?

A

Nuclear radius is directly proportional to the cube root of the nucleon number

31
Q

True or False: the density of a nucleus is independent of its radius?

A

True

32
Q

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

A

E = mc²

33
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

34
Q

Why is there a mass defect?

A

Because energy is needed to bring the parts of a nucleus together, therefore the mass equivalent of the energy is lost and the total mass decreases

35
Q

What is binding energy?

A

The energy required to separate a nucleus into its constituent parts

36
Q

What is nuclear fission?

A

Where a large unstable nucleus splits into 2 smaller nuclei, releasing energy

37
Q

What is nuclear fusion?

A

When 2 small nuclei fuse together to create a large nuclei, releasing large amounts of energy

38
Q

Why is it difficult to make nuclear fusion occur on earth?

A

There is a large repulsion between the 2 positively-chatged nuclei, therefore a lot of energy is required to overcome the repulsion and fuse them together. It is hard to find a material that can withstand the heat

39
Q

How is nuclear fission used in nuclear reactors?

A

Rods of Uranium-235 absorb neutrons and become unstable, causing them to spilt into two daughter nuclei

40
Q

What is the purpose of a moderator in a nuclear reactor?

A

To slow down the neutrons so they travel slow enough to be absorbed by the uranium

41
Q

Why are control rods essential for a nuclear power station?

A

They stop the chain reaction from getting out of control by absorbing neutrons

42
Q

Is Boron used as a control rod or a moderator?

A

Control rod

43
Q

Give an example of a material that can be used as a moderator in a nuclear reactor?

A

Water

44
Q

What is the purpose of using water as a coolant?

A

It allows heat from the nuclear reactor to escape, stopping the reactor from overheating

45
Q

What is the critical mass?

A

The minimum mass of fuel needed for a chain reaction to occur

46
Q

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

A

Spent fuel rods

47
Q

How is high-level waste disposed of?

A

● First stored in cooling ponds
● Then they are put in sealed steel containers and put deep underwater

48
Q

What is low-level waste contained in?

A

They are sealed in containers and put underground until they are safe again

49
Q

Why is the constant density of nuclear material derived from the equation R =R⁰A⅓ only approximate?

A

It assumes a uniform distribution of nucleons within the nucleus

50
Q

How is fission induced?

A

By firing a thermal neutron into the elements nucleus, causing it to become extremely unstable

51
Q

What is binding energy (mass defect ) equal to?

A

Mass of nucleons - Mass of nucleus

52
Q

In a fission reactor, what do the control rods do?

A

Absorb excess neutrons to slow down the chain reaction to stop it from getting out of control

53
Q

In a fission reactor, what does the moderator do?

A

Slows down the neutrons to allow them to be absorbed easier and to sustain the chain reaction

54
Q

What provides evidence for the existence of energy levels in nuclei?

A

The existence of gamma radiation

Physics (14 decks)

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