nuclear physics Flashcards
1
Q
What did Rutherford scattering demonstrate
A
The existence of the nucleus
2
Q
What did scientists believe before Rutherford scattering
A
Thomsons plum pudding
3
Q
What is Thomson’s plum pudding model
A
A sphere of positive charge with small areas of negative charge evenly distributed throughout
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
5
Q
What did the fluorescent coating do in Rutherford scattering
A
You could see where the alpha particles hit inside Of the chamber
6
Q
How was the path of the alpha particles observed in Rutherfords scattering
A
A microscope
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
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
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
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
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
11
Q
What was concluded from Rutherford experiments
A
The atom has a small dense positively charged nucleus at its centre
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.
13
Q
What are the 3 types of radiation
A
Alpha beta gamma
14
Q
What is alphas range in air
A
2-10cm
15
Q
What is betas range in air
A
1m
16
Q
What is gammas range in air
A
Infinite - follows inverse square law
17
Q
How ionising is alpha
A
Highly
18
Q
How ionising is beta
A
Weakly
19
Q
How ionising is gamma
A
Very weakly
20
Q
Are alpha particles deflected by electric and magnetic fields
A
yes
21
Q
Are beta particles deflected by electric anf magnetic fields
A
yes
22
Q
Are gamma rays deflected by electric and magnetic fields
A
no
23
Q
what is alpha absorbed by
A
paper
24
what is beta absorbed by
approx 3mm of aluminium foil
25
what is gamma absorbed by
several meters of concrete or several inches of lead
26
how can the 3 types of radiation be differentiated
different penetrating powers
27
what experiment differentiates between the 3 radiations
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
28
How can radiation be used in material production
To monitor the thickness of the materials
29
How does beta radiation help the production of aluminium foil
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
30
What are the main uses of gamma radiation
As a detector, sterilise surgical equipment, radiation therapy
31
How does gamma radiation work as a detector
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
32
How does gamma radiation sterilise surgical equipment
It kills any bacteria present
33
How does gamma radiation work in radiation therapy
It kills cancerous cells in a targeted region of the body but also healthy cells
34
Methords to reduce risk in radiation therapy
Use of shielding, reduced exposure times
35
How does gamma disperse in the air
Spreads out equally in all directions following an inverse square law
36
How to investigate the inverse square law for gamma
Measure the count rate of a gamma source at different distances from the GM tube, adjusting for background radiation
37
What does it mean if alpha radiation is highly ionising
Incredibly dangerous if inhaled or ingested as it can ionise body tissue
38
Can beta cause damage to body tissue
Yes
39
What does prolonged exposure to gamma cause
Mutation and damage to cells
40
How to safely handle radioactive sources
- 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
41
What is background radiation
Radiation that is always present
42
How to adjust radiation readings to account for background radiation
Measure background radiation first then subtract the value to find the correct count
43
Corrected count =
Total count rate - background count
44
What are sources of background radiation
Radon gas(from rocks)
artificial sources (nuclear weapons testing)
cosmic rays
rocks (containing naturally occurring radioisotopes)
45
What type of process is radioactive decay
A random one
46
What is a decay constant
Probability of a nucleus decaying per unit time
47
How do you calculate decay constant
Change in number of nuclei over time over initial number of nuclei
48
How can you estimate the nuclear radius of an atom
Calculate the distance of closest approach of a charged particle
49
What happens as a charged particle moves towards a positively charged nucleus
Experiences an electrostatic force of repulsion and slows down since kinetic energy is converted to electric potential
50
What is the distance of closest approach
The point at which the particle stops and has no kinetic energy
51
What is the other method for calculating nuclear radius (Not distance of closest approach)
Electron diffraction
52
Why is distance of closest approach not an accurate estimate
It is an overestimate
53
Why do electrons not interact with nucleons in the nucleus through strong nuclear force
They are leptons
54
How does electron diffraction estimate the nuclear radius
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
55
What is the formula for the estimate of nuclear radius from electron diffraction
Sinx = [0.61(lambda)]/R
56
what is the approx size of a radius of a nuclei
1x10^-15
57
what is the graph of nuclear radius (y) and nucleon number (a)
58
how does nuclear density differ
it doesn't, it is constant for all values
59
what is the approx nuclear density
1.45x10^17
60
what does the fact that nuclear density is so great suggest
the atom is mostly empty space with most of its mass concentrated in its centre
61
what is half life
time taken for the number of radioactive nuclei to half
62
why is the time taken for the number of nuclei to halve constant
the decay is exponential
63
what is a more accurate way to measure Half life
plotting a graph of ln(initial nuclei) against time as the modulus of the gradient of the line is the decay constant
64
what is the activity of a radioactive sample
number of nuclei that decay per second
65
what is the activity of a radioactive sample proportional to
number of nuclei where the decay constant is the constant of proportionality
66
what can the decay constant be used to model
the decay of a nuclei only when there is a large number of nuclei in a sample
67
why can you only use the decay constant to model decay if there is a large number of nuclei
its modelled by statistical means
68
what are two ways the half life of a radioactive nucleus can be used
dating of objects and medical diagnosis
69
how does carbon dating work
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
how does medical diagnosis with radioactive nuclei work
nuclei with a short half life can be used as radioactive tracers in medical diagnosis.
71
what specific element is used in medical diagnosis with radioactive nuclei and why
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
why do the activity and half life of radioactive nuclei affect the way they must be stored
to prevent nuclei with a long half life damaging the environment and people living around them for a long period of time
73
what are nuclei held together by
strong nuclear force
74
what force of repulsion do protons experience
electromagnetic force
75
what happens if the strong nuclear and the electromagnetic force are out of balance
the nuclei becomes unstable and will experience decay
76
what are the 4 reasons why a nucleus may become unstable
too many neutrons, too many protons, too many nucleons, too much energy
77
what does a nucleus with too many neutrons decay through
beta minus and one of the neutrons changes to a proton, beta minus and antineutrino is released
78
what does a nucleus with too many protons decay through
beta plus or electron capture
79
what is beta plus decay
proton changes into a neutron and a beta plus particle and neutrino is released
80
what is electron capture
an orbiting electron is taking in by the nucleus and combined with a proton causing formation of neutron and neutrino
81
what does a nucleus with too many nucleons decay through
alpha emission
82
what does a nucleus with too much energy decay through
gamma emission (usually occurs after another type of decay as nucleus becomes excited and has excess energy)
83
why doesn't the number of neutrons and protons in a stable nucleus increase uniformly beyond 20 of each
the electromagnetic force of repulsion becomes larger than the strong nuclear force keeping the nucleus together
84
what happens when more neutrons are added to a nucleus
distance between protons increases decreasing magnitude of electromagnetic force
85
How can nuclear decay be represented other than equations
Energy level diagrams
86
How does an element in an excited nuclear state go to ground state
Emits a gamma photon
87
Why is technetium-99m good for medical diagnosis
Emits pure gamma source so easily detected by cameras, weakly ionising, short half life of 6 hours, easily prepared on site
88
graph of number of neutrons against number of protons and the areas in which what type of decay will occur
89
what are energy level diagrams
diagrams that show the differences in energy of particles
90
what state is technetium formed in
an excited state
91
what is shown on an energy level diagram is a source is formed in an excited state
ground state and gamma photon is drawn on
92
what is the mass defect/mass difference
the difference in mass between a nucleus and the mass of its constituents
93
what happens to the mass "lost" in mass defect
converted into energy and released when the nucleons fuse to form a nucleus
94
what is the binding energy of a nucleus
energy required to separate the nucleus into its constituents ( or energy released when a nucleus is formed from its constituents)
95
what is one atomic mass unit
1/12th the mass of a carbon-12 atom
96
what does a change of 1u in mass mean in terms of energy
931.5 MeV of energy is released
97
what is nuclear fission
splitting of a large nucleus into two daughter nuclei
98
where does nuclear fission occur
large unstable nuclei
99
how does nuclear fission occur
randomly but can also be induced
100
why is energy released during nuclear fission
the smaller daughter nuclei have a higher binding energy per nucleon
101
what is nuclear fusion
where two smaller nuclei join together to form one larger nucleus
102
why is energy released during fusion
the larger nucleus has a much higher binding energy per nucleon
103
does fusion or fission release more energy
fusion
104
why can fusion only occur at extremely high temperatures
a massive amount of energy is required to overcome electrostatic force of repulsion between nuclei
105
how can you identify if an element will undergo fission or fusion
plotting a graph of binding energy per nucleon against nucleon number
106
what element has the highest binding energy per nucleon
iron
107
what do nuclei smaller than iron undergo
fusion
108
what do nuclei greater than iron undergo
fission
109
where is nuclear fission used
nuclear power plants to create electricity without emission of greenhouse gasses
110
what is a risk of using nuclear fission in power plants
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
what allows society to make informed decisions about how electricity should be generated
understanding nuclear physics behind production of nuclear power
112
how can fission be induced
by firing a thermal neutron into uranium nucleus causing it to become extremely unstable
113
why is the fact that thermal neutrons have a low energy useful
they can induce fission
114
why cant neutrons with a higher energy cause fission
they rebound away from uranium after a collision
115
what are the products of fission
2 daughter nuclei and at least one neutron
116
what does the neutron released in fission go onto cause
more fission causing a chain reaction where each fission causes at least one more fission
117
what is critical mass
minimum mass of fuel required to maintain a steady chain reaction
118
what does using exactly the critical mass of fuel mean
a single fusion reaction follows the last continuing indefinitely
119
what does using less than the critical mass of fuel mean
the reaction would eventually stop
120
what are the 3 key features of a nuclear reactor
moderator, control rods, coolant
121
what do moderators do
slow down the neutrons released in fission reactions to thermal speeds
122
how do moderators slow down neutrons
through elastic collisions between the nuclei of the moderator atoms and fission neutrons
123
the closer the moderator atoms are in size to a neutron the.......
large the proportion of momentum which is transferred so lower collisions to get neutrons to thermal speeds
124
why is water used as a moderator
it contains hydrogen, inexpensive, not very reactive
125
what is sometimes used as a moderator
graphite
126
what do control rods do
absorb neutrons in the reactor in order to control chain reactions
127
what are control rods made of
materials that absorb neutrons without undergoing fission e.g. boron and cadmium
128
why can the height of the control rods be controlled
to control the rate of fission reactions which controls amount of energy produced
129
what does coolant do
absorbs heat released during fission reactions in the core of the reactor
130
what is the heat absorbed by the coolant used for
to make steam which powers electricity generating turbines
131
why is water also used as a coolant
high specific heat capacity
132
what other materials can be used as a coolant
molten salt or a gas e.g. helium
133
what is the fuel used in nuclear reactors called
enriched uranium
134
how is enriched uranium formed
enrichment of mined uranium which is 99% U-238
135
what does the fact that U 238 doesn't experience fission do
increases percentage of U 235 to 5%
136
what does u-238 do
absorbs fission neutrons so controls rate of fission reactions
137
how are the fuel rods inserted into the reactor
remotely to limit workers exposure
138
what is around a nuclear reactor
a thick concrete shielding which blocks radiation escaping the reactor and harming workers in power station
139
what may happen to the shielding after long term use
it may become radioactive
140
why may the shielding become radioactive
neutrons which escape the reactor may enter the shielding nuclei causing them to become unstable and experience beta minus decay
141
what happens in an emergency in nuclear reactors
control rods dropped into the reactor core entirely to stop fission reactions
142
how does dropping control rods stop fission entirely
absorbs all free neutrons in core
143
what is it called when control rods are dropped into the core entirely
emergency shut down
144
what is the diffraction pattern of electrons
concentric circles with a central bright stop that get dimmer from the centre
145
at the nuclear level, are mass and energy interchangeable
yes
146
what is lower when measuring mass of nucleus and mass of constituents
mass of nucleus is always lower
147
where is the mass lost when converting constituents to a nucleus
converted to energy and released when nucleons form
148
what are daughter nucleus stability and activity
extremely unstable and have a high activity
149
what are spent fuel rods
used up fuel rods
150
what type of waste are spent fuel rods
high level waste ( dangerous)
151
what is low level waste
contains short-lived radioactivity
152
examples of low level waste
tools and gloves
153
how can low level waste be disposed
close to surface
154
why can low level waste be disposed close to surface
won't take long to stop being radioactive
155
how long can high level waste be radioactive for
thousands of years
156
how is high level waste removed and handled
remotely to reduce exposure
157
where are materials removed from the reactor placed
in a cooling pond for up to a year
158
why are materials removed from a reactor very hot
due to fission reactions
159
where are cooling ponds usually located and why
on same site or very close by so they don't have to travel long distances to reduce risk of exposure
160
what is removed from spent fuel rods after cooling
plutonium or useable uranium to be recycled
161
what happens to the spent fuel rods after plutonium or useable uranium is removed
it is vitrified and placed in thick steel casks, stored in deep caverns in geologically stable locations
162
what is vitrification
encasement in glass
163
why is high level waste stored in geologically stable locations
so no chance of waste coming free of its casing
164
how are locations to store radioactive waste chosen
so they make minimal impact on environment
people living in the are are consulted beforehand
165
how much power does 1kg of uranium give in comparison to coal
25 tonnes of coal
165
pros of nuclear power stations
no polluting gas, reliable power, need far less fuel
166
cons of nuclear power stations
produce radioactive waste, nuclear meltdowns are catastrophic
167
how are risks in nuclear power stations minimised
via safety aspects
168
do benefits or risks outweigh each other for nuclear power stations
benefits outweigh the risk
169
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