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nuclear physics Flashcards

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1
Q

What did Rutherford scattering demonstrate

A

The existence of the nucleus

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2
Q

What did scientists believe before Rutherford scattering

A

Thomsons plum pudding

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3
Q

What is Thomson’s plum pudding model

A

A sphere of positive charge with small areas of negative charge evenly distributed throughout

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4
Q

What equipment is used in Rutherford scattering

A

Alpha source and gold foil in an evacuated chamber which was covered in a fluorescent coating

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5
Q

What did the fluorescent coating do in Rutherford scattering

A

You could see where the alpha particles hit inside Of the chamber

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6
Q

How was the path of the alpha particles observed in Rutherfords scattering

A

A microscope

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7
Q

What were the expected results if plum pudding model was true

A

They would be deflected by a small amount when passing through the foil

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8
Q

What were the 3 observations in scattering experiment

A

Most passed through the foil with no deflection

a small amount were deflected by a large angle

A few particles were deflected back by more than 90 degrees

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9
Q

What did the fact that a small amount of particles were deflected by a large angle tell us

A

That the centre of the atom is positively charged

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9
Q

What did the fact that most alpha particles passed straight through gold foil with no deflection tell us

A

That the atom was mostly empty space and not a uniform density

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10
Q

What did the fact that very few particles were deflected back by more than 90 degrees tell us

A

That the centre of the atom was very dense and very small

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11
Q

What was concluded from Rutherford experiments

A

The atom has a small dense positively charged nucleus at its centre

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12
Q

What is radiation

A

Where an unstable nucleus emits energy in the form of em waves or subatomic particles in order to become more stable.

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13
Q

What are the 3 types of radiation

A

Alpha beta gamma

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14
Q

What is alphas range in air

A

2-10cm

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15
Q

What is betas range in air

A

1m

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16
Q

What is gammas range in air

A

Infinite - follows inverse square law

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17
Q

How ionising is alpha

A

Highly

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18
Q

How ionising is beta

A

Weakly

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19
Q

How ionising is gamma

A

Very weakly

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20
Q

Are alpha particles deflected by electric and magnetic fields

A

yes

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21
Q

Are beta particles deflected by electric anf magnetic fields

A

yes

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22
Q

Are gamma rays deflected by electric and magnetic fields

A

no

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23
Q

what is alpha absorbed by

A

paper

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24
Q

what is beta absorbed by

A

approx 3mm of aluminium foil

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25
Q

what is gamma absorbed by

A

several meters of concrete or several inches of lead

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26
Q

how can the 3 types of radiation be differentiated

A

different penetrating powers

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27
Q

what experiment differentiates between the 3 radiations

A

A Geiger-muller tube and counter to find background count when source isn’t present.

Place the source of radiation close to the GM and measure count rate

place paper/aluminium/lead between the source and GM and measure again.

Depending on which decreases tells you what source it is

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28
Q

How can radiation be used in material production

A

To monitor the thickness of the materials

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29
Q

How does beta radiation help the production of aluminium foil

A

The beta source is on one side of the material, detector on the other

if too thick less passes through foil

if too thin more passes through foil

rollers adjust depending on reading

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30
Q

What are the main uses of gamma radiation

A

As a detector, sterilise surgical equipment, radiation therapy

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31
Q

How does gamma radiation work as a detector

A

A radioactive source with a short half life that emits gamma radiation which can be injected into a patient and then can be detected using gamma cameras

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32
Q

How does gamma radiation sterilise surgical equipment

A

It kills any bacteria present

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33
Q

How does gamma radiation work in radiation therapy

A

It kills cancerous cells in a targeted region of the body but also healthy cells

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34
Q

Methords to reduce risk in radiation therapy

A

Use of shielding, reduced exposure times

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35
Q

How does gamma disperse in the air

A

Spreads out equally in all directions following an inverse square law

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36
Q

How to investigate the inverse square law for gamma

A

Measure the count rate of a gamma source at different distances from the GM tube, adjusting for background radiation

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37
Q

What does it mean if alpha radiation is highly ionising

A

Incredibly dangerous if inhaled or ingested as it can ionise body tissue

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38
Q

Can beta cause damage to body tissue

A

Yes

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39
Q

What does prolonged exposure to gamma cause

A

Mutation and damage to cells

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40
Q

How to safely handle radioactive sources

A
  • Use long handled tongs
  • store source in a lead lined container
  • keep source far away from people as possible
  • never point source towards a person
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41
Q

What is background radiation

A

Radiation that is always present

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42
Q

How to adjust radiation readings to account for background radiation

A

Measure background radiation first then subtract the value to find the correct count

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43
Q

Corrected count =

A

Total count rate - background count

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44
Q

What are sources of background radiation

A

Radon gas(from rocks)

artificial sources (nuclear weapons testing)

cosmic rays

rocks (containing naturally occurring radioisotopes)

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45
Q

What type of process is radioactive decay

A

A random one

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46
Q

What is a decay constant

A

Probability of a nucleus decaying per unit time

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47
Q

How do you calculate decay constant

A

Change in number of nuclei over time over initial number of nuclei

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48
Q

How can you estimate the nuclear radius of an atom

A

Calculate the distance of closest approach of a charged particle

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49
Q

What happens as a charged particle moves towards a positively charged nucleus

A

Experiences an electrostatic force of repulsion and slows down since kinetic energy is converted to electric potential

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50
Q

What is the distance of closest approach

A

The point at which the particle stops and has no kinetic energy

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51
Q

What is the other method for calculating nuclear radius (Not distance of closest approach)

A

Electron diffraction

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52
Q

Why is distance of closest approach not an accurate estimate

A

It is an overestimate

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53
Q

Why do electrons not interact with nucleons in the nucleus through strong nuclear force

A

They are leptons

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54
Q

How does electron diffraction estimate the nuclear radius

A

They are accelerated to high speeds so that their de broglie wavelength is around 10^-15

they are directed at a thin film of material causing them to diffract between gaps between nuclei

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55
Q

What is the formula for the estimate of nuclear radius from electron diffraction

A

Sinx = [0.61(lambda)]/R

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56
Q

what is the approx size of a radius of a nuclei

A

1x10^-15

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57
Q

what is the graph of nuclear radius (y) and nucleon number (a)

A
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58
Q

how does nuclear density differ

A

it doesn’t, it is constant for all values

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59
Q

what is the approx nuclear density

A

1.45x10^17

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60
Q

what does the fact that nuclear density is so great suggest

A

the atom is mostly empty space with most of its mass concentrated in its centre

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61
Q

what is half life

A

time taken for the number of radioactive nuclei to half

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62
Q

why is the time taken for the number of nuclei to halve constant

A

the decay is exponential

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63
Q

what is a more accurate way to measure Half life

A

plotting a graph of ln(initial nuclei) against time as the modulus of the gradient of the line is the decay constant

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64
Q

what is the activity of a radioactive sample

A

number of nuclei that decay per second

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65
Q

what is the activity of a radioactive sample proportional to

A

number of nuclei where the decay constant is the constant of proportionality

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66
Q

what can the decay constant be used to model

A

the decay of a nuclei only when there is a large number of nuclei in a sample

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67
Q

why can you only use the decay constant to model decay if there is a large number of nuclei

A

its modelled by statistical means

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68
Q

what are two ways the half life of a radioactive nucleus can be used

A

dating of objects and medical diagnosis

69
Q

how does carbon dating work

A

carbon-14 has a long half life so it can used to date organic objects by measuring the current amount of c14 and comparing to initial amount (initial amount is similar in all living things)

70
Q

how does medical diagnosis with radioactive nuclei work

A

nuclei with a short half life can be used as radioactive tracers in medical diagnosis.

71
Q

what specific element is used in medical diagnosis with radioactive nuclei and why

A

technetium 99m as it is a pure gamma emitter with a half life of 6 hours. short enough half life to limit exposure but long enough for tests and can be prepared on site

72
Q

why do the activity and half life of radioactive nuclei affect the way they must be stored

A

to prevent nuclei with a long half life damaging the environment and people living around them for a long period of time

73
Q

what are nuclei held together by

A

strong nuclear force

74
Q

what force of repulsion do protons experience

A

electromagnetic force

75
Q

what happens if the strong nuclear and the electromagnetic force are out of balance

A

the nuclei becomes unstable and will experience decay

76
Q

what are the 4 reasons why a nucleus may become unstable

A

too many neutrons, too many protons, too many nucleons, too much energy

77
Q

what does a nucleus with too many neutrons decay through

A

beta minus and one of the neutrons changes to a proton, beta minus and antineutrino is released

78
Q

what does a nucleus with too many protons decay through

A

beta plus or electron capture

79
Q

what is beta plus decay

A

proton changes into a neutron and a beta plus particle and neutrino is released

80
Q

what is electron capture

A

an orbiting electron is taking in by the nucleus and combined with a proton causing formation of neutron and neutrino

81
Q

what does a nucleus with too many nucleons decay through

A

alpha emission

82
Q

what does a nucleus with too much energy decay through

A

gamma emission (usually occurs after another type of decay as nucleus becomes excited and has excess energy)

83
Q

why doesn’t the number of neutrons and protons in a stable nucleus increase uniformly beyond 20 of each

A

the electromagnetic force of repulsion becomes larger than the strong nuclear force keeping the nucleus together

84
Q

what happens when more neutrons are added to a nucleus

A

distance between protons increases decreasing magnitude of electromagnetic force

85
Q

How can nuclear decay be represented other than equations

A

Energy level diagrams

86
Q

How does an element in an excited nuclear state go to ground state

A

Emits a gamma photon

87
Q

Why is technetium-99m good for medical diagnosis

A

Emits pure gamma source so easily detected by cameras, weakly ionising, short half life of 6 hours, easily prepared on site

88
Q

graph of number of neutrons against number of protons and the areas in which what type of decay will occur

A
89
Q

what are energy level diagrams

A

diagrams that show the differences in energy of particles

90
Q

what state is technetium formed in

A

an excited state

91
Q

what is shown on an energy level diagram is a source is formed in an excited state

A

ground state and gamma photon is drawn on

92
Q

what is the mass defect/mass difference

A

the difference in mass between a nucleus and the mass of its constituents

93
Q

what happens to the mass “lost” in mass defect

A

converted into energy and released when the nucleons fuse to form a nucleus

94
Q

what is the binding energy of a nucleus

A

energy required to separate the nucleus into its constituents ( or energy released when a nucleus is formed from its constituents)

95
Q

what is one atomic mass unit

A

1/12th the mass of a carbon-12 atom

96
Q

what does a change of 1u in mass mean in terms of energy

A

931.5 MeV of energy is released

97
Q

what is nuclear fission

A

splitting of a large nucleus into two daughter nuclei

98
Q

where does nuclear fission occur

A

large unstable nuclei

99
Q

how does nuclear fission occur

A

randomly but can also be induced

100
Q

why is energy released during nuclear fission

A

the smaller daughter nuclei have a higher binding energy per nucleon

101
Q

what is nuclear fusion

A

where two smaller nuclei join together to form one larger nucleus

102
Q

why is energy released during fusion

A

the larger nucleus has a much higher binding energy per nucleon

103
Q

does fusion or fission release more energy

A

fusion

104
Q

why can fusion only occur at extremely high temperatures

A

a massive amount of energy is required to overcome electrostatic force of repulsion between nuclei

105
Q

how can you identify if an element will undergo fission or fusion

A

plotting a graph of binding energy per nucleon against nucleon number

106
Q

what element has the highest binding energy per nucleon

A

iron

107
Q

what do nuclei smaller than iron undergo

A

fusion

108
Q

what do nuclei greater than iron undergo

A

fission

109
Q

where is nuclear fission used

A

nuclear power plants to create electricity without emission of greenhouse gasses

110
Q

what is a risk of using nuclear fission in power plants

A

daughter nuclei are radioactive and need to be stored safely for thousands of years, meltdowns are also a possibility which cause harm to environment

111
Q

what allows society to make informed decisions about how electricity should be generated

A

understanding nuclear physics behind production of nuclear power

112
Q

how can fission be induced

A

by firing a thermal neutron into uranium nucleus causing it to become extremely unstable

113
Q

why is the fact that thermal neutrons have a low energy useful

A

they can induce fission

114
Q

why cant neutrons with a higher energy cause fission

A

they rebound away from uranium after a collision

115
Q

what are the products of fission

A

2 daughter nuclei and at least one neutron

116
Q

what does the neutron released in fission go onto cause

A

more fission causing a chain reaction where each fission causes at least one more fission

117
Q

what is critical mass

A

minimum mass of fuel required to maintain a steady chain reaction

118
Q

what does using exactly the critical mass of fuel mean

A

a single fusion reaction follows the last continuing indefinitely

119
Q

what does using less than the critical mass of fuel mean

A

the reaction would eventually stop

120
Q

what are the 3 key features of a nuclear reactor

A

moderator, control rods, coolant

121
Q

what do moderators do

A

slow down the neutrons released in fission reactions to thermal speeds

122
Q

how do moderators slow down neutrons

A

through elastic collisions between the nuclei of the moderator atoms and fission neutrons

123
Q

the closer the moderator atoms are in size to a neutron the…….

A

large the proportion of momentum which is transferred so lower collisions to get neutrons to thermal speeds

124
Q

why is water used as a moderator

A

it contains hydrogen, inexpensive, not very reactive

125
Q

what is sometimes used as a moderator

A

graphite

126
Q

what do control rods do

A

absorb neutrons in the reactor in order to control chain reactions

127
Q

what are control rods made of

A

materials that absorb neutrons without undergoing fission e.g. boron and cadmium

128
Q

why can the height of the control rods be controlled

A

to control the rate of fission reactions which controls amount of energy produced

129
Q

what does coolant do

A

absorbs heat released during fission reactions in the core of the reactor

130
Q

what is the heat absorbed by the coolant used for

A

to make steam which powers electricity generating turbines

131
Q

why is water also used as a coolant

A

high specific heat capacity

132
Q

what other materials can be used as a coolant

A

molten salt or a gas e.g. helium

133
Q

what is the fuel used in nuclear reactors called

A

enriched uranium

134
Q

how is enriched uranium formed

A

enrichment of mined uranium which is 99% U-238

135
Q

what does the fact that U 238 doesn’t experience fission do

A

increases percentage of U 235 to 5%

136
Q

what does u-238 do

A

absorbs fission neutrons so controls rate of fission reactions

137
Q

how are the fuel rods inserted into the reactor

A

remotely to limit workers exposure

138
Q

what is around a nuclear reactor

A

a thick concrete shielding which blocks radiation escaping the reactor and harming workers in power station

139
Q

what may happen to the shielding after long term use

A

it may become radioactive

140
Q

why may the shielding become radioactive

A

neutrons which escape the reactor may enter the shielding nuclei causing them to become unstable and experience beta minus decay

141
Q

what happens in an emergency in nuclear reactors

A

control rods dropped into the reactor core entirely to stop fission reactions

142
Q

how does dropping control rods stop fission entirely

A

absorbs all free neutrons in core

143
Q

what is it called when control rods are dropped into the core entirely

A

emergency shut down

144
Q

what is the diffraction pattern of electrons

A

concentric circles with a central bright stop that get dimmer from the centre

145
Q

at the nuclear level, are mass and energy interchangeable

A

yes

146
Q

what is lower when measuring mass of nucleus and mass of constituents

A

mass of nucleus is always lower

147
Q

where is the mass lost when converting constituents to a nucleus

A

converted to energy and released when nucleons form

148
Q

what are daughter nucleus stability and activity

A

extremely unstable and have a high activity

149
Q

what are spent fuel rods

A

used up fuel rods

150
Q

what type of waste are spent fuel rods

A

high level waste ( dangerous)

151
Q

what is low level waste

A

contains short-lived radioactivity

152
Q

examples of low level waste

A

tools and gloves

153
Q

how can low level waste be disposed

A

close to surface

154
Q

why can low level waste be disposed close to surface

A

won’t take long to stop being radioactive

155
Q

how long can high level waste be radioactive for

A

thousands of years

156
Q

how is high level waste removed and handled

A

remotely to reduce exposure

157
Q

where are materials removed from the reactor placed

A

in a cooling pond for up to a year

158
Q

why are materials removed from a reactor very hot

A

due to fission reactions

159
Q

where are cooling ponds usually located and why

A

on same site or very close by so they don’t have to travel long distances to reduce risk of exposure

160
Q

what is removed from spent fuel rods after cooling

A

plutonium or useable uranium to be recycled

161
Q

what happens to the spent fuel rods after plutonium or useable uranium is removed

A

it is vitrified and placed in thick steel casks, stored in deep caverns in geologically stable locations

162
Q

what is vitrification

A

encasement in glass

163
Q

why is high level waste stored in geologically stable locations

A

so no chance of waste coming free of its casing

164
Q

how are locations to store radioactive waste chosen

A

so they make minimal impact on environment

people living in the are are consulted beforehand

165
Q

how much power does 1kg of uranium give in comparison to coal

A

25 tonnes of coal

165
Q

pros of nuclear power stations

A

no polluting gas, reliable power, need far less fuel

166
Q

cons of nuclear power stations

A

produce radioactive waste, nuclear meltdowns are catastrophic

167
Q

how are risks in nuclear power stations minimised

A

via safety aspects

168
Q

do benefits or risks outweigh each other for nuclear power stations

A

benefits outweigh the risk

169
Q
A
170
Q
A

physics (4 decks)

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