Nuclear Flashcards
(124 cards)
1
Q
What was the Thomson Model of the atom
A
Thomson model of the atom, also known as the ‘plum pudding’ model. This model said that atoms were made up of a globule of positive charge, with negatively charged electrons sprinkled in it
2
Q
Explain the Rutherford’s Scattering experiment
A
A stream of alpha particles from a radioactive source was fired at very thin gold foil.
When alpha particles from a radioactive source strike a fluorescent screen, a tiny visible flash of light is produced. Geiger and Marsden recorded these flashes, and counted the number of alpha particles scattered at different angles.
If the Thomson model was right, all the flashes should have been seen within a small angle of the beam. This wasn’t what they saw.
See pg 160 for diagram
3
Q
What were the observations for the alpha particle scattering experiment
A
Geiger and Marsden observed that most alpha particles went straight through the foil, but a few scattered at angles greater than 90°, sending them back the way they came.
4
Q
What were Rutherfords Conclusions from the experiments?
A
- Most of the fast, charged alpha particles went straight through the foil. So the atom is mainly empty space.
- Some of the alpha particles were deflected through large angles, so the centre of the atom must have a large, positive charge to repel them. Rutherford named this the nucleus.
- Very few particles were deflected by angles greater than 90 degrees, so the nucleus must be tiny and most of the mass must be in the nucleus (dense), since the fast alpha particles (with high momentum) are deflected by the nucleus.
So most of the mass and the positive charge in an atom must be contained within a tiny, central nucleus.
5
Q
What is the proton number, what it symbol
A
The proton number is sometimes called the atomic number, and has the symbol Z.
Z is just the number of protons in the nucleus.
6
Q
What defines and element?
A
The proton number (no two elements have the same)
7
Q
What is the nucleon number
A
The nucleon number is also called the mass number, and has the symbol A.
It tells you how many protons and neutrons are in the nucleus.
8
Q
What is an isotope
A
Atoms with the same number of protons but different numbers of neutrons are called isotopes.
9
Q
How does changing the number of neutrons affect an atom’s properties?
A
Changing the number of neutrons doesn’t affect the atom’s chemical properties.
The number of neutrons affects the stability of the nucleus though.
Unstable nuclei may be radioactive.
10
Q
What is the strong nuclear force ?
A
To hold the nucleus together, the strong nuclear force must be an attractive force that overcomes the electrostatic force. (the repulsive force between the positive charges of the protons)
11
Q
How does strong nuclear force work with distance?
A
Experiments have shown that the strong nuclear force between nucleons has a short range. It can only hold nucleons together when they are separated by up to a few femtometres - the size of a nucleus.
The strength of the strong nuclear force between nucleons quickly falls beyond this distance.
12
Q
How does the size of the strong nuclear force vary with the interaction of different nucleons
A
Experiments also show that the strong nuclear force works equally between all nucleons. This means that the size of the force is the same whether proton-proton, neutron-neutron or proton-neutron.
13
Q
What happen to the nuclear force at small separations
A
At very small separations, the strong nuclear force must be repulsive - otherwise there would be nothing to stop it crushing the nucleus to a point.
14
Q
What does a graph of strong nuclear force against electrostatic force look like
What are the Axis
A
See CGP page 164
Y axis : repulsion / attraction
X axis: nucleus separation
15
Q
What cause nucleus instability?
A
- too many neutrons
- too many nucleons in total (too heavy)
- too few neutrons
- too much energy in the nucleus
16
Q
What happens during nucleus decay
A
The nucleus decays by releasing energy and/or particles (nuclear radiation), until it reaches a stable form - this is called radioactive decay.
17
Q
How do you predict when a specific particle will undergo radioactive decay
A
An individual radioactive decay is spontaneous and random
- it can’t be predicted.
18
Q
Is it possible to predict the decaŷ of a large number of nuclei
A
Although you can’t predict the decay of an individual nucleus, if you take a very large number of nuclei, their overall behaviour shows a pattern.
6)
Any sample of a particular isotope (p.161) has the same rate of decay, i.e. the same proportion of nuclei will decay in a given time
19
Q
What is nuclear fission
A
Heavy nuclei (e.g. uranium), are unstable. Some can randomly split into two smaller nuclei (and sometimes several neutrons) — this is called nuclear fission.
20
Q
What does spontaneous or induced mean in terms of nuclear fission
A
This process is called spontaneous if it just happens by itself, or induced if we encourage it to happen.
21
Q
Do flash cards on the different types of radiation
A
..
22
Q
Why is energy released during nuclear fission?
A
Energy is released during nuclear fission because the new, smaller nuclei have a higher binding energy per nucleon and a lower total mass.
23
Q
Are larger nuclei more or less likely to undergo fission than smaller nuclei and why
A
More likely because larger nuclei are less stable
24
Q
Why are there only a certain number of elements, explain using nuclear spontaneous nuclear fission
A
This means that spontaneous fission limits the number of nucleons that a nucleus can contain
- in other words, it limits the number of possible elements.
25
How can fission be induced
Fission can be induced by making a neutron enter a 235U nucleus, causing it to become very unstable.
26
What is a name for a neutron that cab be absorbed by the nucleus
A low energy neutron is called a thermal neutron. Only low energy neutrons can be captured in this way by the nucleus
27
What is the fuel used for nuclear fission in a reactor
Nuclear reactors use rods of uranium that are rich in 235U as 'fuel' for fission reactions. (The rods also contain a lot of 238U, but that doesn't undergo fission.)
28
How does a chain reaction occur in a nuclear reactor
These fission reactions produce more neutrons which then induce other nuclei to fission — this is called a chain reaction.
29
For a neutron to contribute to the chain reaction having been released what must happen to it and what causes this
The neutrons will only cause a chain reaction if they are slowed
cool water
down, which allows them to be captured by the uranium nuclei
- these slowed down neutrons are called thermal neutrons.
4) 235U fuel rods need to be placed in a moderator (for example, water) to
moderaton (water)
pump
slow down and/or absorb neutrons. You need to choose a moderator that will slow down some neutrons enough so they can cause further fission, keeping the reaction going at a steady rate.
30
What is critical mass?
You want the chain reaction to continue on its own at a steady rate, where one fission follows another.
The amount of 'fuel' you need to do this is called the critical mass — any less than the critical mass (sub-critical mass) and the reaction will just peter out. Nuclear reactors use a supercritical mass of fuel (where several new fissions normally follow each fission) and control the rate of fission using control rods.
31
What do control rods do?how are they used in an emergency?
Control rods control the chain reaction by limiting the number of neutrons in the reactor. They absorb neutrons so that the rate of fission is controlled. Control rods are made up of a material that absorbs neutrons (e.g. boron), and they can be inserted by varying amounts to control the reaction rate.
In an emergency, the reactor will be shut down automatically by the release of the control rods into the reactor, which will stop the reaction as quickly as possible.
32
What is coolant in a nuclear reactor used to do
Coolant is sent around the reactor to remove heat produced in the fission — often the coolant is the same water that is being used in the reactor as a moderator. The heat from the reactor can then be used to make steam for powering electricity-generating turbines.
33
What happens when fission is left unchecked with an example of how this is used
the chain reaction in a nuclear reactor is left to continue unchecked, large amounts of energy are released in a very short time.
Many new fissions will follow each fission, causing a runaway reaction which could lead to an explosion. This is what happens in a fission (atomic) bomb.
34
Pro and cons of Nuclear Fission Power Plants
Deciding whether or not to build a nuclear power station (and if so, where to build it) is a tricky business.
2)
Nuclear fission doesn't produce carbon dioxide, unlike burning fossil fuels, so it doesn't contribute to global warming (p.69). It also provides a continuous energy supply, unlike many renewable sources (e.g. wind/solar).
3)
4)
However, some of the waste products of nuclear fission are highly radioactive and difficult to handle and store.
When material is removed from the reactor, it is initially very hot, so it is placed in cooling ponds until the temperature falls to a safe level. The radioactive waste is then stored in sealed containers in specialist facilities until its activity has fallen sufficiently. This can take many years, and there's a risk that material could escape from these containers. A leak of radioactive material could be harmful to the environment and local human populations both now and in the future, particularly if the material contaminated water supplies.
5)
Accidents or natural disasters pose a risk to nuclear reactors. In 2011 an earthquake and subsequent tsunami in Japan caused a meltdown at the Fukushima nuclear power plant. Over 100 000 people were evacuated from the area, and many tonnes of contaminated water leaked into the sea. The perceived risk of this kind of disaster leads many people to oppose the construction of nuclear power plants near their homes.
6)
Because of all of the necessary safety precautions, building and decommissioning nuclear power plants is very time-consuming and expensive.
35
What is nuclear fusion
Two light nuclei can combine to create a larger nucleus.
This is called nuclear fusion.
36
What type of fusion happens in the sun (with an equation)
In the Sun, hydrogen nuclei fuse to form helium:
See CGP for equation
37
What must nuclei overcome to undergo fusion
Nuclei can only fuse if they have enough energy to overcome the electrostatic (Coulomb) repulsion between them, and get close enough for the strong interaction to bind them.
38
What are the conditions required for fusion to occur
This means fusion reactions require much higher temperatures than fission, as well
as high pressures (or high densities). Under such conditions, generally only found inside stars, matter turns into a state called a plasma.
39
Why is energy released during nuclear fusion?
A lot of energy is released during nuclear fusion because the new, heavier nucleus has a much higher binding energy per nucleon (and so a lower total mass). The energy released helps to maintain the high temperatures needed for further fusion reactions.
40
Energetically which is better fusion or fission?
Although the energy released per reaction is generally lower in nuclear fusion than fission, the nuclei used in fusion have a lower mass, so a mole of the reactants in a fusion reaction weighs less than a mole of the reactants in a fission reaction. Gram for gram, fusion can release more energy than fission.
41
Do we currently have fusion reactors?
No, scientists are trying to develop fusion reactors so that we can generate nuclear electricity without the waste you get from fission reactors, but they haven't yet succeeded in creating one that makes more electricity than it uses.
42
Not expiation booklet
P=p0e^ht
43
What is the equation that relates nuclear radius to nucleon number ?
R=r0A^1/3
R is radius of nucleus
r0 is constant equal to 1.4x10^-15 or 1.4fm
A is nucleon number
44
Generally what is the value of nuclear density
Roughly 10^17kgm^-3
(Could be worth knowing to check answer)
45
What does the fact nuclear density is higher than atomic density suggests
Most of an atoms mass is in its nucleus
The nucleus is small compared to the atom
An atom must contain a lot of empty space
46
What are hadrons
Particles that feel the strong nuclear force
47
what is fundamental particle
fundamental particle is a subatomic particle that is not composed of other particles.
48
Are hadrons are fundamental particle
No - they are made up of quarks
49
What are some example of hadrons
Protons and neutrons are hadrons. This is why they can make atomic nuclei — the nucleus of an atom is made up from protons and neutrons held together by the strong nuclear force
there are other hadrons that you don't get in normal matter, like sigmas and mesons
50
Which hadrons decay
Most hadrons will eventually decay into other particles.
The exception is protons — most physicists think that protons don't decay.
51
Do neutrons decay, if so how and why
The neutron is an unstable particle that decays into a proton.
(But it's much more stable when it's part of a nucleus.) It's really just an example of B- decay, which is caused by the weak nuclear force.
See equation in CGP
52
What are leptons
Leptons are fundamental particles and they don't feel the strong nuclear force. They interact with other particles via the weak nuclear force and gravity (and the electromagnetic force if they're charged).
53
What are the leptons we need to know
There are two types of lepton you need to know about
— electrons (e) which should be familiar, and neutrinos (v).
54
Describe a neutrinos mass and charge
Neutrinos have zero (or almost zero) mass and zero electric charge
Neutrinos only take part in weak interactions
55
Complete anti particle sheet on good notes
56
What is the equation that explains Einstein’s theory of relativity
Δ E= Δ mc^2
57
What are two interpretations that can be made from Einstein’s theory of relativity
**The first is that mass is a form of energy**. The interaction of an electron-positron pair illustrates this idea well - the particles completely destroy each other (annihilation) and the entire mass of the particles is transformed into two gamma photons.
**The second interpretation is that energy has mass**. The change in mass Δ m of an object, or a system, is related to the change in its energy Δ E by the equation Δ E = Δ mc. A moving ball has kinetic energy, implying that its mass is greater than its rest mass.
58
What is the rule for when energy is converted into mass ?
When energy is converted into mass you get equal amounts of matter and antimatter.
59
What happens when two protons are fired at each other with high speed
Fire two protons at each other at high speed and you'll end up with a lot of energy at the point of impact.
This energy might be converted into more particles.
If an extra proton is formed then there will always be an antiproton to go with it. It's called pair production.
60
What can be produced from a high energy photon
Each Particle-Antiparticle Pair is Produced from a Single Photon. Pair production only happens if one photon has enough energy to produce that much mass.
61
Where does pair production tend to take place
It tends to take place near a nucleus (which helps conserve momentum
62
What particle-antiparticle pair is most commonly produced by a photon ?
You usually get electron-positron pairs produced (rather than any other pair) — because they have a relatively low mass.
63
What is the minimum energy a photon must have to produce a particle antiparticle pair
The minimum amount of energy the photon must have is the combined energy of the two particles at rest (i.e. assuming that the particles have negligible kinetic energy).
64
How can you calculate the minimum energy that a photon must be have, to produce a particle anti-particle pair
Pg 167 green box
65
Why shown on a diagram the electron and positron produced from a photon have curved tracks, why?
The particle tracks are curved because there's usually a magnetic field present in particle physics experiments. They curve in opposite directions because of the opposite charges on the electron and positron.
66
What is it called when a particle meets an antiparticle
Annihilation
67
Describe annihilation
All the mass of the particle and antiparticle gets converted to energy, in the form of a pair of photons. In ordinary matter antiparticles can only exist for a fraction of a second before this happens, so you won't see many of them.
Just like with pair production, you can calculate the minimum energy of each photon produced (i.e. assuming that the particles have negligible kinetic energy).
68
What equation can you use to calculate the energy of the the two photons produced during annihilation
The combined energy of the photons will be equal
to the combined energy of the particles, so 2E = 2mc^2 and so E = mc^2
69
What equation can find the minimum energy a photon must have to emit of particle-antiparticle pair
E=2mc^2
Where E is the minimum energy and m is the rest mass of each particle
70
What are quarks
Quarks are the building blocks for hadrons like protons and neutrons.
71
What are the quarks we need to be aware of
Up (u) , down (d) and strange (s)
72
What are the anti particles of hadrons made of ?
Anti quarks
73
Complete quarks and anti quarks tables
.
74
What is the evidence for quarks
Evidence for quarks came from hitting protons with high energy electrons.
The way the electrons scattered showed that there were three concentrations of charge (quarks) inside the proton.
75
Quark composition of proton
uud
76
Quark composition of neutron
udd
77
What are baryons
Protons and neutrons are a type of hadron called baryons, which are made up of three quarks.
78
What are mesons
There are also hadrons made up of a quark and an anti-quark, called mesons
79
What happens if you blast a proton with energŷ
The energy just gets changed into more quarks and antiquarks — it's pair production again and it makes mesons
See the diagram pg 168
80
How do hadrons decay ?
Weak nuclear force
81
What is beta minus decay
In beta-minus (3) decay a neutron is changed into a proton — in other words udd changes into uud. It means turning a d quark into a u quark.
See pg 169
82
What is beta plus decaŷ
Some unstable isotopes like carbon-11 decay by beta-plus (B*) emission. In this case a proton changes to a neutron, so a u quark changes to a d quark.
83
What is conserved in all particle interaction.
In any particle reaction, the total charge after the reaction must equal the total charge before the reaction.
84
How can you investigate the penetration of different types of radiation
CGP pg 171
85
What is conserved in every nuclear reaction
What does this mean for decay occasions
Decay equations need to be balanced - in every nuclear reaction, including fission and fusion, charge and nucleon number must be conserved.
Energy and momentum are also conserved in all nuclear reactions.
86
What type of nuclei have alpha emissions
Why do they have these emissions
Alpha emission only happens from the nuclei of very heavy atoms like uranium and radium.
The nuclei of these atoms are too massive to be stable.
87
What happens to the original element when an alpha particle is emitted
When an alpha particle is emitted, the proton number decreases by two, and the nucleon number decreases by four.
88
What type of nuclei have beta minus decay
ß(minus)-decay happens in isotopes that are 'neutron rich' (have many more neutrons than protons in their nucleus).
89
What is release during beta minus decay
Beta-minus decay is the emission of an electron from the nucleus along with an antineutrino
(One of the neutrons in the nucleus decays into a proton and ejects a beta-minus particle
(an electron) and an antineutrino)
90
What happens to the nucleon number of the original element after beta minus decay
When a beta-minus particle is emitted, the proton number increases by one, and the nucleon number stays the same.
91
What is released during beta plus decay
In beta-plus emission, a proton gets changed into a neutron, releasing a positron and a neutrino.
92
What happens to the nucleon numbers of the original element in beta plus decay
The proton number decreases by one, and the nucleon number stays the same.
93
When is gamma radiation emitted from a nuclei
Gamma rays can be emitted from a nucleus with excess energy (we say the nucleus is excited)
94
What happens to the nucleon number of the original nuclei during gamma emissions
During gamma emission, there is no change to the nuclear constituents the nucleus just loses excess energy.
95
What is the activity
The number of nuclei that decay each second
96
What is the activity of a sample proportional to?
The size of the sample
97
What is the decay constant
What does a bigger decay constant mean
The decay constant measure how quickly an isotope will decay
The bigger the decay constant λ the faster the rate of decay
98
What is the decay constants units
s^-1
99
Equation to find activity from decay constant
A= λN
activity = decay constant x number of undecayed nuclei
100
What is activity measured in
Activity is measured in becquerels (Bq).
An activity of 1 Bq means that 1 nucleus decays per second (s^-1).
101
Equation to find activity
A= - ΔN/Δt
Where Δt is the change in time
Where ΔN is the change in the number of undecayed nuclei
Negative sign is used because ΔN is alway negative
102
What is an equation for rate a change of undecayed nuclei
-ΔN/Δt = λN
λ is the decay constant
ΔN/Δt is the rate of change of the number of undecayed nuclei
N is the number of undecayed nuclei
103
How can you model radioactive decay using a spreadsheet?
CGP page 173
104
What is the half life of an isotope?
The half-life of an isotope is the average time it takes for the number of undecayed nuclei to halve.
105
What is the count rate?
The count rate is the number of decays detected per second (it's lower than the activity).
106
How can you generate a count rate decaŷ graph experimentally
CGP 174
107
Equation to find the decay constant using half life
λt(1/2) = ln 2
108
How can you find the number of undecayed nuclei remaining after a period of time
N=N₀e^(-λ t)
N = is the number of undecayed nuclei remaining
N ₀= is the original number of nuclei
λ= decay constant
t = is time
109
How can you find the activity of decaying nuclei after a period of time
A=A₀e^(-λt)
A= activity at time t
A ₀=original activity
λ = decay constant
t = time
110
What radioactive isotope is used in carbon dating
Carbon - 14
111
How does carbon dating work ?
1) Living plants take in carbon dioxide from the atmosphere as part of photosynthesis, including the radioactive isotope carbon-14. Animals then take this carbon-14 in when they eat the plants. All living things contain the same percentage of carbon-14.
2) When they die, the activity of carbon-14 in the plant starts to fall, with a half-life of around 5730 years.
3) Archaeological finds made from once-living material (like wood) can be tested to find the current amount of carbon-14 in them. This can be used to calculate how long the material has been dead for — i.e. how old it is.
112
Do the carbon dating Q in images
…
113
What is mass defect
The difference in the mass of a nucleus to the mass of its constituent parts
114
Why does mass defect occur
As nucleons join together, the total mass decreases - this 'lost' mass is converted into energy and released. The amount of energy released is equivalent to the mass defect
You can calculate the energy released from Einstein’s equation of relativity
115
What is the binding energy
The energy needed to separate all of the nucleons in a nucleus is called the binding energy (measured in MeV), and it is equivalent to the mass defect.
116
What is the conversion into Kgs from atomic mass units
1u= 1.661x10^-27kg
117
How do you calculate binding energy per unit of mass defect
Binding energy / mass defect
118
How do you calculate binding energy per nucleon
Binding energy (B)/ Nucleon Number (A)
119
What does a graph of binding energy per nucleon look like
See CGP page 176
120
Where do the most stable nuclei occur on a graph or binding energy against nucleon number
the most stable nuclei occur around the maximum point on the graph — which is at nucleon number 56 (i.e. iron,
121
How does binding energy change in fusion and how does this effect energy released
Combining small nuclei is called nuclear fusion this increases the binding energy per nucleon
Binding Energy per dramatically, which means a lot of energy is released during nuclear fusion.
122
What is fission and how does binding energy change during it.
Fission is when large nuclei are split in two — the nucleon numbers of the two new nuclei are smaller than the original nucleus, which means there is an increase in the binding energy per nucleon.
So, energy is also released during nuclear fission (but not as much energy per nucleon as in nuclear fusion).
123
How can you use the binding energy per nucleon to estimate the energy released from nuclear reactions?
See CGP page 177
124
How do you draw the beta decays as equations
CGP pg 172
