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Physics A Level > 6.4 Nuclear and Particle Physics > Flashcards

6.4 Nuclear and Particle Physics Flashcards

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1
Q

How was Rutherford’s experiment set up? (3)

A

Alpha source opposite gold foil (approximately 400 atoms thick)
Zinc sulphide detector set at different angles
Done in a vacuum to stop air molecules from deflecting the alpha particles

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2
Q

What did the results of Rutherford’s experiment indicate about the structure of an atom? (3)

A

Most particles passed through undeviated - atoms are mostly empty space
1 in 2000 were deflected through small angles - nucleus is positively charged
1 in 8000 rebounded - small, dense concentrated region of positive charge

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3
Q

What is the approximate radius of a nucleus?

A

10^-15

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4
Q

What is the approximate radius of an atom?

A

10^-10

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5
Q

Define proton number

A

The number of protons/electrons in an atom

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6
Q

Define nucleon number

A

The number of protons and neutrons in the nucleus

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7
Q

Define isotope (2)

A

A nucleus of the same element with the same number of protons but a different number of neutrons
Isotopes all undergo the same chemical reactions

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8
Q

What is the strong nuclear force? (3)

A

The force that allows the protons to stay together despite the electrostatic repulsion
Repulsive below 0.5fm
Attractive to about 3fm

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9
Q

How does the density of nuclei compare to the density of atoms?

A

Nuclei are very small, concentrated regions of mass so it is extremely dense compared to ordinary matter

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10
Q

What are antiparticles? (2)

A

Every particle has a corresponding antiparticle with the same mass and opposite charge
When a particle and antiparticle meet they annihilate, producing a high-energy pair of photons

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11
Q

What forces act on hadrons? (2)

A

Strong nuclear force

Weak nuclear force

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12
Q

What forces act on leptons?

A

Weak nuclear force

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13
Q

What are some examples of hadrons? (2)

A

Protons

Neutrons

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14
Q

What are some examples of leptons? (2)

A

Electrons

Neutrinos

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15
Q

Fundamental forces - strong nuclear (4)

A

Experienced by nucleons
10^-15 m
Binds nucleus
Exchange particle - gluon

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16
Q

Fundamental forces - electromagnetic (4)

A

Experienced by static and moving charged particles
Infinite range
Binds atoms
Exchange particle - photon

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17
Q

Fundamental forces - weak nuclear (3)

A

Responsible for beta-decay
10^-18 m
Exchange particle - W+/- and Z bosons

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18
Q

Fundamental forces - gravitational (2)

A

Experienced by all particles with mass

Binds solar system

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19
Q

What is a fundamental particle?

A

A particle that has no internal structure meaning that it can’t be divided

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20
Q

What are baryons?

A

Hadrons made up of three quarks

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21
Q

What are mesons?

A

Hadrons made up of two quarks (quark and anti-quark)

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22
Q

Charge on quarks - up

A

+ 2/3 e

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23
Q

Charge on quarks - down

A
  • 1/3 e
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24
Q

Charge on quarks - charm

A

+ 2/3 e

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25
Q

Charge on quarks - strange

A
  • 1/3 e
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26
Q

Charge on quarks - top

A

+ 2/3 e

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27
Q

Charge on quarks - bottom

A
  • 1/3 e
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28
Q

What is the quark composition of a proton?

A

up, up, down

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29
Q

What is the quark composition of a neutron?

A

up, down, down

30
Q

Baryon number - up, charm, top

A

+ 1/3

31
Q

Baryon number - down, strange, bottom

A

+ 1/3

32
Q

Lepton number - electron, tauon, muon

A

+ 1

33
Q

Lepton number - neutrinos

A
  • 1
34
Q

Strangeness - strange quark

A
  • 1
35
Q

What is beta-minus decay?

A

neutron > proton + electron + anti-electron neutrino

36
Q

What is beta-plus decay?

A

proton > neutron + positron + electron neutrino

37
Q

What are the conservation laws in emission equations? (4)

A

Charge
Nucleon and proton number
Baryon number
Lepton number

38
Q

What is alpha radiation? (4)

A

A helium nucleus
Charge = + 2e
Very ionising
Very short range - absorbed by thin sheet of paper

39
Q

What is beta radiation? (4)

A

Fast-moving electrons
Charge = -e
Less ionising than alpha radiation
Range of about 1 metre - absorbed by 1-3 mm of aluminium

40
Q

What is gamma radiation? (4)`

A

High-energy photons
Travel at the speed of light, carrying no charge
Least ionising
Long range - absorbed by a few centimetres of lead

41
Q

How can the absorption of different forms of radiation be investigated? (2)

A

Set up a radioactive source opposite a GM tube, with an absorber between them
Measure the background radiation first in order to produce a corrected count rate after the experiment

42
Q

When does gamma decay take place?

A

When a nucleus has surplus energy following an alpha or beta emission

43
Q

Why is radioactive decay random? (2)

A

It is impossible to predict when a particular nucleus in the sample will decay
Each nucleus in the sample has the same chance of decaying per unit time

44
Q

Why is radioactive decay spontaneous? (2)

A

It is not affected by the presence of other nuclei in the sample
It is not affected by external factors like pressure

45
Q

Define half-life

A

The average time it takes for half the number of active nuclei in the sample to decay

46
Q

Define activity

A

The rate at which nuclei decay

47
Q

What does activity depend on? (2)

A

The number of undecayed nuclei present

The half-life of the isotope

48
Q

What is the decay constant?

A

The probability of decay of an individual nucleus per unit time

49
Q

How can half-life be measured experimentally? (3)

A

Determine the background count rate
Use a GM tube to record a 10 second count every half-minute
Plot a graph of corrected count rate against time to find half-life

50
Q

What is carbon dating? (2)

A

The ratio of radioactive carbon-14 from the atmosphere to carbon-12 is measured in an artefact
The half-life of carbon-14 is used to calculate the age of the artefact

51
Q

What is the half-life of carbon-14?

A

5700 years

52
Q

What are the limitations of carbon dating? (2)

A

Assumes ratio of C-12:C-14 has remained constant over time whereas CO2 emissions, solar flares and testing nuclear bombs may have caused it to change
The activity of C-14 is very small and comparable to the background count rate

53
Q

Why does carbon dating not work on rocks?

A

They do not contain carbon

Carbon-14 would have a half life that is too short to date rocks

54
Q

What is used to date rocks?

A

Rubidium-87 because it has a half life of 49 billion years

55
Q

What is mass?

A

A form of energy

56
Q

How does mass change in radioactive decay? (2)

A

The mass of the daughter nuclei must be less than the mass of the parent nuclei as energy has also been released
The decrease in mass is equivalent to the energy released

57
Q

Define mass defect

A

The difference between the mass of the completely separated nucleons and the mass of the nucleus

58
Q

What causes the mass defect?

A

Work is done to separate the nucleons in a nucleus so the total mass of the separated nucleons must be greater than the mass of the nucleus

59
Q

Define binding energy

A

The minimum energy required to completely separate a nucleus into its constituent nucleons

60
Q

What does the graph of binding energy per nucleon against nucleon number show? (5)

A

For nuclei below iron, binding energy increases with nucleon number
For nuclei above iron, binding energy decreases with nucleon number
Iron is the most stable nucleus
Fusion takes place up to iron
Fission takes place in nuclei above iron

61
Q

What is the process of induced fission? (3)

A

Uranium-235 undergoes fission when it absorbs a slow neutron, forming U-236
U-236 decays into two daughter nuclei (often barium and krypton) and releasing three neutrons
The change in mass causes energy to be released

62
Q

Why does fission cause a chain reaction?

A

Three neutrons are released which can go on to react cause fission in other nuclei

63
Q

Structure of a fission reactor - fuel rods

A

Spaced evenly within steel reactor core

64
Q

Structure of a fission reactor - coolant

A

Removes thermal energy produced within the fissile fuel

65
Q

Structure of a fission reactor - moderator (2)

A

Slows down fast neutrons by causing a transfer of KE through collisions
Uses cheap and readily available materials - usually `H-2 as this causes a larger change in KE

66
Q

Structure of a fission reactor - control rods (3)

A

Absorb neutrons to control the chain reaction
Raised or lowered in the core to ensure that one neutron survives each reaction
Usually boron or cadmium

67
Q

What is the environmental impact of nuclear fission? (3)

A

U-238 readily absorbs neutrons, quickly decaying into plutonium-239
Plutonium-239 is extremely toxic, radioactive and has a very long half-life
High level waste must be buried deep underground on secure sites to avoid food and water supplies

68
Q

Why are high temperatures needed for nuclear fusion?

A

The nuclei need to be moving fast enough to overcome the electrostatic repulsion between them

69
Q

Why is high pressure needed for nuclear fusion?

A

It moves the nuclei close enough to fuse

70
Q

How would a nuclear fusion reactor be constructed? (3)

A

Superconducting coils - provide high current and strong magnetic field with zero resistivity at temperatures just above 0K
Lithium blanket - source of tritium fuel, used to remove heat and slow down neutrons
Water is heated to produce steam and turn turbine

71
Q

What are the advantages of fusion over fission? (2)

A

Safer

There is enough fuel to provide power for millions of years

72
Q

What must be true about binding energy for a nuclear reaction to release energy? (2)

A

Binding energy must increase

This decreases the energy in the nucleus, showing that some has been released

Physics A Level (23 decks)

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