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Physics A Level > Nuclear > Flashcards

Nuclear Flashcards

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1
Q

Who posited the plum pudding model?

A

J J Thomson.

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2
Q

Describe the plum pudding model.

A

A cloud of positive charge with negative electrons inside of it.

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3
Q

Who disproved Thomson’s plum pudding model?

A

Rutherford.

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4
Q

How did Rutherford disprove Thomson?

A

The gold-foil experiment.

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5
Q

How does the gold foil experiment work?

A

Get a thin sheet of gold

Fire + charged alpha particles at it

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6
Q

What is expected to happen in the gold foil experiment according to Thomson?

A

The alpha particles should go straight through.

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7
Q

What actually happened in the gold foil experiment, why?

A

Some alphas bounce back, hit the positive nucleus.

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8
Q

How do we know the nucleus is small and dense?

A

Because most alphas pass straight through the nucleus.

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9
Q

Who discovered neutrons?

A

Chadwick.

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10
Q

What is r?

A

Shortest distance between the nucleus and alpha particles.

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11
Q

When alpha is scattered through 180 degrees what = KE?

A

EPE, particle loses KE and gains EPE.

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12
Q

What speed is the alpha particle at just before it bounces back and changes direction?

A

0.

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13
Q

Ek=Ep= ?. Define all terms.

A

Qn(qa) / 4π(ε0)r

Qn= charge of nucleus
qa = charge of alpha
ε0 = permittivity of free space
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14
Q

What is permittivity of free space?

A

A constant, the capacity of an electric field to permeate a vacuum.

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15
Q

What is the charge of an alpha?

A

2 x 1.6 x10^-19

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16
Q

What is electron diffraction used to measure?

A

The size of the nucleus.

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17
Q

How do we do electron diffraction in this context? What is observed?

A

Shoot an electron beam through thin metal foil at a screen. Minima and maxima are observed like light diffraction experiments.

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18
Q

What is the equation for the first minimum in electron diffraction? Define all terms.

A

Sinθ = 1.22λ / 2R

λ = wavelength (duh)
R = radius of the nucleus of the atoms that scatter the e-s
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19
Q

What is the equation for the de Broglie wavelength of electrons?

A

λ = hc / E

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20
Q

What does the graph of relative intensity against angle of diffraction look like?

A

Quadrants 1 and 2. Big peak in the centre becomes tiny peak becomes even tinier. Symmetrical.

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21
Q

What is the size of the radius of a typical atom?

A

5 x10^-11m

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22
Q

Why is the nucleus so small?

A

Because SNF only works at very short distances (<3fm).

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23
Q

Describe the graph of nuclear radius against mass number A.

A

Steep increase then plateaus.

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24
Q

What is the equation for nuclear radius? Define all terms. What does this show?

A

R = R0 A^1/3

R = nuclear radius
R0 = 1.4fm
A = number of nucleons/mass number

R is proportional to the cube root of A.

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25
Q

What is the equation for nuclear density? Define all terms.

A

ρ = 3m / 4π(R0)^3

ρ = density
m = mass
R0 = 1.4fm
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26
Q

Why does radiation happen, what does the atom actually do?

A

When the nucleus of an atom is unstable, atom chucks something out of the nucleus.

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27
Q

How do we speed radioactive decay up?

A

We can’t.

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28
Q

On an A-Z graph what nuclear decay happens above the line of stability?

A

Beta minus, nuclei have too many neutrons.

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29
Q

On an A-Z graph what nuclear decay happens below the line of stability?

A

Beta plus, nuclei have too many protons.

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30
Q

What happens to very heavy nuclei?

A

Alpha decay, nuclei have too many nucleons.

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31
Q

What does every decay conserve?

A

Energy, charge, momentum, baryon number, lepton number.

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32
Q

How do you find unknowns from energy level diagrams?

A

Find equations for delta E, list all values given, rearrange equations and solve for unknown.

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33
Q

What does more ionising mean, how does this affect range and penetration depth?

A

Reacts with more matter, shorter range and penetration depth.

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34
Q

Why is radiation being in cells bad?

A

Once in cells can damage DNA.

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35
Q

What does high radiation do to cells?

A

Kills them completely.

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36
Q

What does low radiation do to cells?

A

Damages DNA, causes mutations and can lead to cancer.

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37
Q

What medical applications do we use radiation for?

A

See how fluids move around the body, radiotherapy.

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38
Q

How do we use radiation to see how fluids move around the body?

A

Give patient a small amount of radiation. detect the radiation as it’s being pushed around the body.

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39
Q

How do we use radiotherapy to treat cancer patients? Is this easy?

A

Using radiation to kill cancer cells, not easy, can’t kill too many normal cells as well.

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40
Q

What non medical uses are there for radiation (not power either)?

A

Detecting leaks in underground pipes, smoke alarms.

41
Q

Define irridation.

A

Objects near a radioactive source get exposed to radiation (they do not become radioactive).

42
Q

Define contamination.

A

When you get a radioactive atom on you (bad), atoms decay and cause you harm.

43
Q

How can we reduce exposure to radiation?

A

Using lead shielding, remote controlled robot arms etc.

44
Q

Define radiation dose, what is this measured in?

A

Amount of radiation you’ve been exposed to, sieverts Sv.

45
Q

Where does background radiation come from?

A

Radioactive rocks in the earth
Space, radiation from sun/ cosmic rays
Man made, nuclear power stations, waste, accidents

46
Q

What does background radiation depend on?

A

Location and occupation.

47
Q

How does location effect background radiation?

A

Granite rocks, give off radioactive radon gas.

High altitude, less protection from cosmic rays by the atmosphere.

48
Q

How does occupation effect background radiation?

A

Nuclear power plant workers

Radiographers

49
Q

What is the power output of a blackbody?

A

Amount of energy it emits per second, P = E/t.

50
Q

I = ? using terms. Define all terms.

A

P/A.

I = Intensity, W/m^2
P = power, W
t = time, s
51
Q

I = ? using a constant. Define all terms.

A

I = k/r^2

I = Intensity, W/m^2
k = constant
r = distance from source, m
52
Q

What is the law connecting intensity and distance called?

A

Inverse square law.

53
Q

Is intensity and distance an inverse square law in actuality? Why or why not?

A

Not really, only gamma looks like this. Alpha and beta are absorbed easily so radiation drops off more quickly.

54
Q

Define activity, give the units.

A

Number of decays per second. Becquerels, Bq or counts per minute, cpm.

55
Q

How do we measure decay?

A

In half life.

56
Q

Define half life.

A

Time it takes for amount of radioactive stuff to go down by half.
Time for activity to go down by half.

57
Q

N(t) = ? Define all terms and give all units.

A

N(t) = No e^-λt

N(t) = mass after time, kg
No = starting mass, kg
λ = decay constant, s^-1
t = time, s
58
Q

N = ? using moles. Define all terms and give units.

A

N = n NA

N = number of atoms
n= number of moles
NA = Avagadro's constant
59
Q

Give activity = ? as rate of change.

A
  • rate of change of unstable nuclei

- A = -dN/dt

60
Q

A = ? using N. Define all terms and give units.

A

A = λN

A = activity, Bq
λ = decay constant, s^-1
N = number of atoms
61
Q

A = ? using Ao. Define all terms and give units.

A

A = Ao e^-λt

A = activity, Bq
Ao = activity we started with, Bq
λ = decay constant, s^-1
t = time, s
62
Q

T1/2 = ?. Define all terms and give units.

A

ln(2)/λ = T1/2

T1/2 = half life, s
λ = decay constant, s^-1
63
Q

When plotting ln(N) over t what is the gradient?

A

λ

64
Q

How does carbon dating work?

A

Living things add C from food
Some is C-14 (radioactive, therefore decays)
Thing dies (aah) and stops adding C
Amount of C goes down by 1/2 every 1/2 life (5700 years)
Look at how much C-14 is left (by percentage)
Work backwards to find age

65
Q

What is the limit to carbon dating, why?

A

Around 50,000 years, not enough C-14 left to get an accurate age.

66
Q

What does E=mc^2 show about the relationship between mass and energy?

A

They are interchangeable.

67
Q

When protons and neutrons are together in a nucleus is their combined mass slightly more, less or the same as the sum of their masses? What is this called?

A

Slightly less, mass defect.

68
Q

How can we explain mass defect?

A

Lost mass released as energy when nucleons bind together.

69
Q

What do we measure mass defect in terms of?

A

u.

70
Q

Define binding energy.

A

The energy needed to separate all the protons and neutrons.

71
Q

b = ? = ?. Define all terms and give units.

A

b = B/A = Δmc^2/A

b = average binding energy per nucleon, J
B = binding energy, J
A = nucleon number
Δm = mass defect, kg
c = speed of light, ms^-1
72
Q

What element is at the peak of the binding energy per nucleon curve? What does this mean it is?

A

Iron, most stable element, most binding energy per nucleon.

73
Q

Below iron on the B per nucleon curve what do we have to do to get energy? What is this called?

A

Adding extra nucleons. fusion.

74
Q

Above iron on the B per nucleon curve what do we have to do to get energy? What is this called?

A

Taking away nucleons/splitting apart nuclei, fission.

75
Q

Define fission.

A

An atom splits into two to become more stable.

76
Q

Define fusion.

A

Two atoms join together to become more stable.

77
Q

What does a heavy unstable nucleus split into?

A

Two light, stable nuclei, energy and fast moving neutrons.

78
Q

Because fission releases neutrons we can get what? Why?

A

A chain reaction. Neutron hits another nuclei (eg. Uranium) and becomes a heavy unstable nuclei, decays.

79
Q

What is conserved in fission?

A

Mass number, atomic number.

80
Q

How do we use controlled and uncontrolled fission chain reactions?

A 
Controlled = nuclear power station
Uncontrolled = atomic bomb
81
Q

How do nuclear power stations control chain reactions?

A

By slowing it down, by absorbing neutrons.

82
Q

What is the function of a control rod? What are they made of?

A

Made of neutron poisons, they absorb neutrons.

83
Q

Do control rods slow neutrons down?

A

No, average KE stays the same.

84
Q

What slows down a chain reaction in a thermal neutron reactor? How?

A

The moderator, slows down fast neutrons and make fission more likely to happen. Slows down by neutrons losing KE in elastic collisions with the molecules in the moderator.

85
Q

What speed are neutrons in a thermal reactor slowed down to, what do we call these?

A

Until they are in thermal equilibrium with the moderator. have the same average KE as surrounding particles. Thermal neutrons.

86
Q

How does the mass of the moderator affect the slowing of the neutrons?

A

Closer in mass to neutrons more they are slowed. Want moderator to be almost the mass of a neutron.

87
Q

Why do fission reactors need shielding? What do we use as shielding?

A

To protect from alpha, beta, gamma and neutron radiation. Concrete or water.

88
Q

What happens to the shielding after time? Why?

A

Becomes radioactive itself, it absorbs neutrons and becomes unstable and decays.

89
Q

What are the two types of radioactive waste?

A

Front end and back end waste.

90
Q

Where does front end waste come from, what does it emit?

A

From the fuel, unused uranium. Emits alpha radiation.

91
Q

Where does back end waste come from, what does it emit?

A

From spent fuel rods. Emits beta and gamma radiation.

92
Q

What type of radioactive waste is more dangerous?

A

Back end waste.

93
Q

What do we do when waste is removed?

A

Place in water to cool (1 year in a ‘spent fuel pool’), then stored in sealed containers (‘dry cask’), then put in steel cylinders surrounded by inert gas, each cylinder surrounded by concrete for radiation shielding.

94
Q

Where does fusion happen?

A

Stars and thermonuclear bombs.

95
Q

What is conserved in fusion?

A

Atomic and neutron numbers.

96
Q

Is the physical mass of a heavy nucleus the same as the sum of the physical masses of the lighter nuclei? Why?

A

No, it’s slightly less. Lost mass goes into energy released.

97
Q

What conditions do we need for fusion?

A

Very high temperatures.

98
Q

What are the benefits of fusion?

A

Almost 0 radioactive waste.

Physics A Level (15 decks)

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