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AQA A Level Physics(Option A: Astrophysics) > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

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1
Q

Describe the ‘plum pudding’ model of the atom

A

Sphere of positive charge with tiny negatively-charged electrons stuck in it

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2
Q

Describe the setup of Rutherford scattering experiment

A
  • A stream of alpha particles from a radioactive source are fired at a very thin gold foil
  • Alpha particles from a radioactive source strike a fluorescent screen, producing a tiny visible flash of light
  • The screen is circular, surrounding the experiment to detect alpha particles scattered at any angle
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3
Q

What was the predicted result of the Rutherford scattering experiment?

A

All the flashes would have been seen within a small angle of the beam

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4
Q

What was the true result of the Rutherford scattering experiment?

A

Most particles passed through the gold foil, some scattered at angles greater that 90 degrees, and few reflected backward

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5
Q

What were the conclusions of the Rutherford scattering experiment?

A
  • The atom must be mostly empty as most of the particles passed through the foil
  • The nucleus must have a very large positive charge as some of the positively charged alpha particles are repelled and deflected by a large angle
  • The nucleus must be tiny as very few alpha particles are deflected by angles greater than 90 degrees
  • Most of the mass must be in the nucleus, since fast moving alpha particles are deflected by the nucleus
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6
Q

What letter is used for the atomic number of an atom?

A

A

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7
Q

What letter is used for the proton number of an atom?

A

Z

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8
Q

What are the 2 methods of estimating values for nuclear radii?

A
  • By using Rutherford’s scattering experiment to calculate the distance to closest approach of a scattered alpha particle
  • Electron diffraction
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9
Q

State the conversion for eV to J

A

1eV = 1.6x10^-19 J

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10
Q

State the closest approach equation

A

Initial KE = Electric Potential = Qq/4πε0r , where r is the distance of closest approach

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11
Q

Why do the electrons from the electron beam have a very high energy in electron diffraction?

A

As the wavelength must be very tiny, 10^-15, to investigate the nuclear radius. λ = hc/E

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12
Q

What is the equation for the first minimum in electron diffraction?

A

sinθ = 1.22λ/2R, where R = the radius of the nucleus the electrons have been scattered by

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13
Q

Describe the graph showing the variation of intensity in an electron diffraction pattern

A
  • A central bright maximum containing the majority of the incident electrons
  • Maximum surrounded by other dimmer maxima
  • The intensity of the maxima decreases as the angle of diffraction increases
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14
Q

State the approximate radius of an atom

A

0.05nm = 5 x 10^-11m

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15
Q

State the approximate radius of an atomic nucleus

A

1fm = 1 x 10^-15m

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16
Q

As the nucleon number increases, what happens to the radius of the nucleus

A

Radius of nucleus increases

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17
Q

What is the relationship between nuclear radius and the cube root of the nucleon number?

A

Directly proportional

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18
Q

What is the value of the constant Ro?

A

1.4fm = 1.4x10^-15m

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19
Q

What is the relationship between nuclear volume and nucleon number, giving the reason?

A
  • Nuclear volume is directly proportional to the nucleon number
  • If R ∝ 3√A, then R³ ∝ A = V ∝ A
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20
Q

Derive the proof that density of nuclear mass is constant

A
  • p = m/V
  • p = A x nucleon mass/4/3πr³
  • p = A x nucleon mass/4/3π(Ro3√A)³
  • p = A x nucleon mass/4/3πRo³A
  • p = 3 x nucleon mass/4πRo³ = constant
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21
Q

Which is greater, nuclear density or atomic density?

A

Nuclear density

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22
Q

State the 3 conclusions about nuclear density being greater than atomic density

A
  • Most of an atom’s mass is in its nucleus
  • The nucleus is small compared to the atom
  • An atom must contain a lot of empty space
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23
Q

What is radioactive decay?

A

When an unstable atom breaks down to become more stable, by releasing energy and/or particles

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24
Q

What is the constituent of alpha radiation?

A

A helium nucleus. 2 neutrons and 2 protons

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25
Q

What is the relative charge of alpha radiation?

A

+2

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26
Q

What is the approximate mass of alpha radiation, in u?

A

4u

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27
Q

What is the constituent of beta-minus(beta) radiation?

A

An electron

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28
Q

What is the relative charge of beta-minus radiation?

A

-1

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29
Q

What is the mass of beta-minus radiation, in u?

A

Negligible

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30
Q

What is the constituent of beta-plus radiation?

A

A positron

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31
Q

What is the relative charge of beta-plus radiation?

A

+1

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32
Q

What is the mass of beta-plus radiation, in u?

A

Negligible

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33
Q

What is the constituent of gamma radiation?

A

A short wavelength, high frequency EM wave

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34
Q

What is the relative charge of gamma radiation?

A

0

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35
Q

What is the mass of gamma radiation, in u?

A

0

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36
Q

What is the penetrating power of alpha radiation?

A

Absorbed by paper, skin or a few centimetres of air

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37
Q

What is the penetrating power of beta-minus radiation?

A

Absorbed by about 3 millimetres of aluminium

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38
Q

What is the penetrating power of gamma radiation?

A

Absorbed by many centimetres of lead, or several centimetres of concrete

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39
Q

Which radiation can pass through thin mica?

A

All of the radiatons

40
Q

Why does beta-plus radiation have no penetrating power?

A

As beta-plus particles almost immediately annihilate with electrons, so they effectively have zero range

41
Q

Describe how to identify the nuclear radiation of an unknown nuclear source

A
  • Record the background count rate with no source present
  • Place the unknown source near a Geiger-Muller tube and record the count rate
  • Place a sheet of paper between the source and tube and record the count rate
  • Replace the paper with a 3mm thick sheet of aluminium and record the count rate
  • For each count rate recorded, subtract the count rate of background radiation
42
Q

What is the ionisation rate of alpha radiation?

A

10,000 ionisations per mm of air

43
Q

State an application of alpha radiation, explaining how it works

A

Smoke alarms: Alpha sources allow current to flow as they can quickly ionise many atoms, but they won’t travel far. When smoke is present, alpha particles can’t reach detector which sets off alarm

44
Q

What is the ionisation rate of beta-minus radiation?

A

100 ionisations per mm of air

45
Q

State an application of beta-minus radiation, explaining how it works

A

Creating sheets of material: A beta source and beta detector are placed either side of a material. The material is passed through adjustable rollers and if too little beta particles are detected, the rollers move closer together and vice versa

46
Q

What is the ionisation rate of gamma radiation?

A

<100 ionisations per mm of air

47
Q

State an application of gamma radiation, explaining how it works

A

PET scan: A radioactive tracer is injected into the bloodstream. Positrons from the tracer annihilate with electrons from the body, producing gamma radiation that can be detected by the scanner

48
Q

Which radiation type has strong ionising power?

A

Alpha radiation

49
Q

Which radiation type has moderately weak ionising power?

A

Beta-minus radiation

50
Q

Which radiation type has very weak ionising power?

A

Gamma radiation

51
Q

Which radiation type has no ionising power?

A

Beta-plus radiation

52
Q

Which radiation type travels at a fast speed?

A

Beta-minus radiation

53
Q

Which radiation type doesn’t have a speed?

A

Beta-plus radiation

54
Q

Which radiation type travels at the speed of light?

A

Gamma radiation

55
Q

Which radiation type travels at a slow speed?

A

Alpha radiation

56
Q

Which radiation types are affected by magnetic fields?

A
  • Alpha radiation
  • Beta-minus radiation
57
Q

Which radiation type are not affected by magnetic fields?

A
  • Beta-plus radiation
  • Gamma radiation
58
Q

Define background radiation

A

The weak level of nuclear radiation found everywhere

59
Q

State 5 types of sources background radiation and what caused them

A
  • The air: Radioactive radon gas is released from rocks, emitting alpha radiation
  • The ground and buildings: Nearly all rock contain radioactive materials
  • Cosmic radiation: Cosmic rays are particles from space which collide with particles in the atmosphere to produce nuclear radiation
  • Living things: All plants and animals contain carbon, some being radioactive carbon-14
  • Man made radiation: Radiation from medical or industrial sources
60
Q

What is the largest contributor to background radiation?

A

The air: Radioactive radon gas released from rocks, emitting alpha radiation

61
Q

Define intensity of radiation

A

The amount of radiation per unit area

62
Q

State the units for intensity

A

W/m²

63
Q

What is the relationship between intensity and distance from the source

A
  • The intensity is inversely proportional to the square of the distance from the source
  • i = k/x² , where k =constant of proportionality
64
Q

Describe the graph of how intensity varies with distance from the source

A
  • As distance from the source increases, the intensity decreases by the square of the distance moved
  • L shaped
  • intensity never touches zero
65
Q

State 4 ways of handling radioactive sources safely

A
  • Keep the source as far away as possible when transporting it
  • Use long handling tongs to minimise radiation absorbed
  • Store the source in a lead box
  • Remove the source from the lead box for the shortest time possible, only when needed
66
Q

What are isotopes?

A

Elements with the same number of protons but a different number of neutrons

67
Q

Define activity

A

The number of unstable nuclei in a radioactive sample decaying per second

68
Q

State the units for activity and what it equates to

A
  • Bq
  • 1Bq = 1 decay per second
69
Q

What is the decay constant?

A

The probability of an unstable nuclei decaying per unit time

70
Q

What does “N” stand for in the equation for activity, A = λN?

A

Number of unstable nuclei in sample

71
Q

What are the units of the decay constant?

A

1/s

72
Q

State the decay equation

A

N = Noe^-λt

73
Q

What is the relationship between the number of unstable nuclei and time?

A

As time increases, the number of unstable nuclei exponentially decreases

74
Q

What is binding energy?

A

Amount of energy needed to divide a nucleus into its constituents

75
Q

Describe the graph of the natural log of the number of unstable nuclei against time

A
  • y intercept is the natural log of the original number of unstable nuclei
  • Constant negative gradient
  • Gradient = -λ
76
Q

What is corrected count rate?

A

The count rate of a radioactive source one the value background count rate is removed

77
Q

What is the decay constant?

A

The probability of a decay happening in a second

78
Q

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

A

To slow down the neutrons to the equivalent of thermal neutrons, to allow fission to occur. Usually water.

79
Q

What is the role of control rods in a nuclear reactor?

A

To absorb excess neutrons to prevent too many fission reactions happening. Usually made of boron.

80
Q

Define half life

A

The average time taken for the number of unstable nuclei in an isotope to half

81
Q

What is a radioisotope?

A

A radioactive isotope

82
Q

State 3 applications of radioactive isotopes

A
  • Radioactive dating
  • Medical diagnosis
  • Storage of radioactive waste
83
Q

What radioisotope is used in radioactive dating?

A

Carbon-14

84
Q

Describe how carbon-14 is used in radioactive dating

A
  • Living plants take in carbon dioxide and carbon-14 from the atmosphere as a part of photosynthesis
  • When they die, the activity of carbon-14 starts to fall
  • The current amount of carbon-14 in the plant is found and this is used to date them
85
Q

State 3 problems of radioactive dating

A
  • The object may have been contaminated by other radioactive sources
  • There may be a high background count that obscures the object’s count
  • There may be uncertainty in the amount of carbon-14 that existed thousands of years ago
  • The sample size or count rate may be too small, and so might be statistically unreliable
86
Q

What radioisotope is mostly used in medical diagnosis?

A

Technetium-99m

87
Q

Describe how medical diagnosis using radioisotopes works

A

A tracer containing technetium-99m is ingested by the patient
- The radiation emitted as it passes through the patient’s body to the region of interest is recorded and an image of inside the patient is produced

88
Q

What is the half-life of technetium-99m?

A

6 hours

89
Q

What is the half-life of carbon-14?

A

Around 5730 years

90
Q

Describe how storage of radioactive waste with radioisotopes works

A
  • Uranium-235 is used in nuclear fission reactors and the radioisotopes it decays into have different half lives
  • These isotopes emit alpha, beta and gamma radiation and must be stored carefully for hundreds of years until their activity falls to safe levels
  • Their long half lives make them dangerous as they make them highly radioactive for a long time
91
Q

State 4 reasons why a nucleus will be unstable

A
  • Too many neutrons
  • Too few neutrons
  • Too much energy
  • Too heavy due to too many nucleons
92
Q

What does alpha emission occur for?

A

Very heavy atoms

93
Q

What does beta-minus emission occur for?

A

Neutron rich isotopes

94
Q

What does beta-plus emission occur for?

A

Proton rich isotopes

95
Q

What does gamma emission occur for?

A
  • Atoms with too much energy
  • There is no change to the nuclear constituents

AQA A Level Physics(Option A: Astrophysics) (15 decks)

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