Most of nuclear Flashcards
(102 cards)
1
Q
What did Rutherfords scattering demonstrate
A
Existence of nucleus
2
Q
Thomsons plum pudding model
A
Sphere of positive charge, small areas of negative charge even distributed
3
Q
Rutherford’s experiment set up
A
Alpha source, gold foil in evacuated chamber covered in fluorescent coating (so you could see when electrons hit), microscope to detect path of alpha particles
4
Q
Plum pudding model Rutherford prediction
A
Positively charged alpha particles would be deflected slightly when passing through foil
5
Q
Rutherford’s experiment results
A
Most alpha passed straight through foil with no deflections, small amount of particles were deflected by large angle, few particles were deteced by more than 90 degrees
6
Q
Range in air of alpha
A
2-10 cm
7
Q
Ionising power of alpha
A
Highly
8
Q
Is alpha deflected by electric and magnetic fields
A
Yes
9
Q
What is alpha absorbed by
A
Paper
10
Q
Range in air of beta
A
1 m
11
Q
Ionising power of beta
A
Weakly
12
Q
Is beta deflected by electric and magnetic fields
A
Yes
13
Q
What is beta absorbed by
A
3mm of aluminium foil
14
Q
Range in air of gamma
A
Infinite (inverse square law)
15
Q
Ionising power of gamma
A
Very weakly
16
Q
Is gamma deflected by electric and magnetic fields
A
No
17
Q
What is gamma absorbed by
A
Several metres of concrete or several inches of lead
18
Q
How to identify a type of radiation due to penetrating power
A
Geiger-muller tube and counter, measure background count, place source near tube, measure, place paper between tube and source, measure, repeat using aluminium foil and several inches of lead until there is a significant decrease in the count rate
19
Q
What can radiation and a geiger-muller tube be used to measure
A
Thickness of a material
20
Q
3 uses of gamma radiation in medicine
A
As a detector, to sterilise, radiation therapy
21
Q
Gamma radiation as a detector
A
Short half life so reduced exposure, injected and detected by gamma cameras to help diagnose
22
Q
Gamma radiation to sterilise
A
Will kill any bacteria present on equipment
23
Q
Gamma radiation radiation therapy
A
Can kill cancerous cells in targeted regions of the body - but will also kill any healthy cells in that region
24
Q
How does gamma move through the air
A
Spreading out in all directions equally - so inverse square law
25
How to investigate the inverse square law
Measure the count rate of a gamma source at different distances from the GM tube (adjust for background radiation), plot a graph of count again 1/(distance)^2 and you will get a straight line
26
How to handle radioactive sources safely
Long handled tongs, lead-lined container, keep the source as far away from self as possible, never point the source directly at anyone
27
How to find the corrected count of a radioactive source
Total count rate - background count
28
Sources of background radiation
Radon gas from rocks, artificial sources (weapon testing/nuclear meltdowns), cosmic rays (from space), rocks containing naturally occuring radioactive isotopes
29
What is a constant decay propability
Denoted by lambda, known as decay constant, change in the number of nuclei over time over initial number of nuclei, so: -(lambda)(initial number of nuclei) = (change in nuber of nuclei) / (time)
30
Shape of radioactive decay curve over a long period of time
Exponentially decreasing
31
Formula for exponential decay
N = (N_0)e^(-lambda x time)
32
N = (N_0)e^(-lambda x time) what is N
Number of nuclei
33
N = (N_0)e^(-lambda x time) what is N_0
Initial number of nuclei
34
N = (N_0)e^(-lambda x time) what is lambda
Decay constant
35
Half life formula
T_1/2 = ln(2) / lambda
36
Activity formula
A = (lambda)(N)
37
Activity exponential decay formula
A = (A_0)e^(-lambda)(t)
38
Use of radioactive nucleus with a long half-life
Dating of objects (carbon dating)
39
Use of radioactive nucleus with a short half-life
Medical diagnosis, medical tracers such as Technetium-99m, pure gamma emitter, half life of 6 hours, can be easily prepared on site
40
Storage of radioactive nuclei with a long half-life
Underground in steel casks
41
What holds together nuclei
Strong nuclear force
42
Force responsible for protons repulsing
Electromagnetic force
43
Why might a nucleus become unstable
Too many neutrons, too many protons, too many neutrons, too much energy
44
Why is the number of protons and neutrons in a stable nuclei not unifrom beyond 20 of each
Electromagnetic force becomes larger than strong nuclear force so more neutrons are needed to increases distance between protons to decrease magnitude of the electromagnetic force
45
How to represent the energy state in nuclear decays
Energy level diagrams
46
How to estimate the nucleus radius of an atom
Calculate the distance of closest approach of a charged particle
47
How can you estimate the nucelus radius of an atom by calculating the distance of closest apporach of a charged particle
Positively charged nucleus will experience an increasing electrostatic force of repulsion as it moves towards the (positive) nucleus, kinetic turns to potential energy until the particle stops and has no kinetic energy left (closest approach), elec potential is now equal to initial kinetic energy
48
Equation of electric potential
V = (1 / 4(pi)(permitivitty of free space))(Q/r)
49
What is the electric potential
Potential energy per unit charge of a postive charge
50
Equation of electric potential energy
(1 / 4(pi)(permitivitty of air))(Q/r) x Q
51
How accurate is the closest approach estimate for the nucleus radius
Not very, will always be an overestimation
52
Alternative method for estimating the nucleus radius
Electron diffraction
53
How can you estimate the nucelus radius of an atom by electron diffraction
Electrons are leptons so will not interact with nucleons in nucleus through the strong nuclear force, accelerated to very high speeds so that De Broglie wavelength is around 10^-15m, directed at a very think film in front of a screen, causes them to diffract throught the gaps between nuclei and form a diffraction pattern, find diffraction angle so get an estimate of nuclear radius via sin(theta) = 0.61(wavelength) / R
54
How to plot a graph of nuclear radius against nucleon number
ln(R)-ln(A), straight line, y-intercept in ln(K)
55
Nuclear radius formula
R = (R_0)A^1/3
56
Is nucear density constant for all nuclei
Yes
57
Nuclear density formula
Mass / volume
58
Nucelar density final derivation formula
m(nucleon) / 4/3(pi)(R_0)^3 which is a constant value
59
Calculated value of nuclear density
1.45 x 10^17 kgm^-3
60
Mass and energy formula at nuclear level
E = mc^2
61
What is the mass defect / mass difference
Difference in mass between nucleus and mass its constituents
62
Difference between mass of nucleus and its constituents
Mass defect / mass difference - mass of nucleus lower than its constituents
63
Explanation for mass defect
Mass is converted into energy and released when nucleons bind to form a nucleus
64
What is binding energy
Energy required to separate the nucleus into its constituents (or energy released when nucleus formed)
65
What is 1 atomic mass unit (1u) defined as
1/12th of mass of carbon-12 atom
66
How to convert atomic mass unit to kg
x 1.661 x 10^-27
67
How much energy is released in a change of 1u of mass
931.3 MeV
68
What is nuclear fission
Splitting of a large nucleus into 2 daughter nuclei
69
Where and when does nuclear fission occur
Very large, unstable nuclei - randomly but can be induced
70
Why is energy released during fission
Smaller daughter nuclei have a higher binding energy per nucleon
71
What is nuclear fusion
Opposite of fission, where two smaller nuclei join together to form 1 larger nucleus
72
Where does nuclear fusion occur
Fairly small nuclei
73
Why is energy released during fusion
Larger nuclei have a much higher binding energy per nucleon
74
Fusion vs fission - energy release
Fusion releases far more energy than fission
75
Fusion vs fission - temperature
Fusion only occurs in extremely high temperatures due to a large amount of energy being required to overcome the electrostatic force of repulsion between nuclei
76
Example of nuclear fission
Neutron + atom(n) = atom(n+1) = 2 atoms with masses that sum to almost (n+1) + multiple neutrons
77
Example of nuclear fusion
2 atoms = 1 atom = 1 atom + neutron
78
Binding energy per nucleon
Binding energy of nucleus / number of nucleons in the nucleus
79
Element with highest binding energy per nucleon
Iron
80
Elements that undergo fusion
Elements smaller than iron
81
Elements that undergo fission
Elements larger than iron
82
Using a graph to calculate energy released in fission or fusion
Change in energy between nuclei
83
Use of nuclear fission
Nuclear power plants to create energy without emission of greenhouse gases
84
Dangers of nuclear fission
Daughter nuclei are radioactive - need to be stored for thousands of years, meltdowns are always a possibility - harm to environment
85
Statement of understanding for nuclear fission
Understanding nuclear physics behind production of nuclear power allows society to make an informed decision on how electricity should be generated
86
How to induce fission
Firing thermal neutron into the nucleus causing it to become extremely unstable
87
Why does the neutron have to be thermal to induce fission
They have low energy so can induce fission, neutrons with a higher energy rebound away from the nucleus after collision and so don't cause a fission reaction
88
Products of fission
2 daughter nuclei and at least one neutron
89
How fission chain reactions are caused
Neutron(s) emitted from fission cause more fission reactions
90
What is the critical mass
Minimum mass of fuel required to maintain a steady chain reaction
91
Using exactly critical mass =
Single fission reaction follows the last
92
Using < critical mass =
Reaction stops
93
Nuclear reactor key features
Moderator, Control rods, Coolant
94
Moderator in the nuclear reactor
Slows down netrons released to thermal speeds through elastic collisions between nuclei of moderator atoms and fission neutrons
95
Moderator in nuclear reactor - how to choose moderator atoms
Moderator atoms closer in size to a neutron means a large proportion of momentum is transferrered so fewer collisions are required to get the neutrons to thermal speeds
96
Atoms used as moderators in nuclear reactors
Water often used due to hydrogen content - inexpensive and not very reactive, graphite sometimes used
97
Control rods in the nuclear reactor
Absorb neutrons in the reactor in order to control chain reactions
98
How control rods work in nucear reactors
Height of them can be controlled to control that fission reactors occur to control amount of energy produced
99
What are control rods made of in nuclear reactors
Materials that absorv neutrons without undergoing fission - boron or cadmium
100
Coolant in the nuclear reactor
Absorbs the heat released during fission reactions in the core of the reactor, heat is used to make steam which powers electricity generating turbines
101
What is often used as both the coolant and moderator in nuclear reactors and why
Water - high specific heat capacity so can transfer large amounts of thermal energy
102
Alternative coolants to water in nuclear reactors
Molten salt or gas (helium)
