Nuclear Physics Flashcards
(68 cards)
1
Q
Potential energy and radius equation
A
Ep=Qq/4πrε
2
Q
What is an advantage of using electron diffraction to measure radius?
A
They are not affected by the SNF as electrons are leptons
Electrons give greater resolution because shorter wavelengths
3
Q
What are 2 disadvantages of using electron diffraction to measure radius?
A
-Difficult to measure 1st minimum of interference pattern
-Beams must be monoenergetic
4
Q
How to estimate radius of an atom using electron diffraction?
A
Sinθ≈1.22λ/d
5
Q
Equation linking radius and nucleon number
A
R=RoA^1/3
6
Q
What is alpha stopped by?
A
Paper
7
Q
What is beta minus stopped by?
A
Aluminium
8
Q
What is beta plus stopped by?
A
Electron
9
Q
What is gamma stopped by?
A
Lead/steel
10
Q
Alpha range in air
A
2-5 cm
11
Q
Beta minus range
A
1m
12
Q
Beta plus range
A
0m
13
Q
Gamma range
A
Infinite
14
Q
Name 4 sources of background radiation
A
Radon gas
Cosmic rays
X-rays in hospitals (medicine)
Nuclear power
15
Q
What is meant by the random nature of decay?
A
You cannot predict which nuclei will decay next
But the same proportion decay each second
16
Q
Mass and moles equation
A
Mass= moles x molar mass
17
Q
How to calculate number of atoms using moles
A
N=nNa
18
Q
Define decay constant
A
The probability of decay per unit time
19
Q
Why is it difficult to determine a reliable age using carbon dating?
A
-Activity may be hard to distinguish from background radiation
-Source may be contaminated by external sources
20
Q
Half life equation
A
T1/2=ln(2)/λ
21
Q
What decay occurs when there are too many neutrons?
A
Beta minus
22
Q
What decay occurs when there are too many protons?
A
Beta plus
Or electron capture
23
Q
What decay occurs when there’s too much mass?
A
Alpha
24
Q
What decay occurs when there is too much energy?
A
Gamma
25
What is the mass defect?
The difference between the mass of a nucleus and the mass of its individual constituents
26
What is the binding energy?
The energy needed to separate a nucleus into its constituent protons and neutrons
The energy released when a nucleus is formed from its individual constituents
27
Neutron number against proton number graph
Straight line until (20,20)
Then curved up to (80,120)
28
What is nuclear fusion and how is energy released?
-2 nuclei combine to form a large nucleus
-The binding energy per nucleon of the final nucleus is higher than for the original nuclei
-The binding energy has not gone into extra energy is released
29
What is nuclear fission and how is energy released?
-A nucleus is split into 2 daughter nuclei
-The binding energy of the daughter nuclei is higher than the original
-The mass defect per nucleon is higher
-Extra mass is released as energy
30
Why is nuclear fusion harder to initiate than nuclear fission?
The electrostatic force makes it hard to get the nuclei close enough for the SNF to work.
So more kinetic energy is needed.
31
Why might is be preferable to use fusion rather than fission?
-Fuel for fusion is more abundant.
-Products produced from fusion are not radioactive.
32
How must fuel waste be treated when it’s removed from the reactor?
-Place in **cooling ponds** for a year.
-Should be **handled remotely**.
-Place in **steel containers**.
-Place the containers deep underground in **geologically stable places**
-Crash resistant casing during transportation
-Long half life (radioactive for 1000s of years)
33
How do the control rods work?
They are lowered into the reactor
They absorb neutrons
This stops them moving inbetween fuel rods
Control rods can be lowered slightly to slow the reaction reducing power output
Can be lowered completely to stop reaction
34
How does the coolant work?
-This removes some of the heat produced by fission.
-Typically water
35
How does the moderator work?
-Fuel rods are placed in the moderator
-The neutrons collide with the moderator molecules.
- This slows them down and they reach thermal equilibrium with the molecules
-Only slow neutrons can be absorbed by U-235
36
What’s the main source of highly radioactive waste from a nuclear reactor?
Daughter nuclei
37
Define background radiation
Radiation that is always in the background, has been there for a long time and doesn’t come from a specific source
38
What graph do you plot when doing inverse square law experiment?
Intensity against 1/distance^2
39
What radiation may be emitted from an excited nucleus in the moderator?
-Gamma
-Because energy gaps are large because the nucleus de excites through the discrete energy levels
40
Why are the nuclei of most atoms of low nucleon number stable?
SNF acts and is larger than electrostatic
This holds the nucleons together
41
Why should the gold foil be thin?
So the alpha particles are only scattered once
42
Why does the scattering experiment demonstrate the nucleus is positively charged?
Some alpha particles are deflected more than 90 degrees
43
Why do stable nuclei have more neutrons than protons?
Neutrons only provide the attractive SNF
This holds the nucleus together
44
How does the neutron and proton number change during beta minus?
Neutron number down by 1
proton number up by 1
45
How does the binding energy arise?
Work is done on nucleons by SNF
46
Define induced fission
A nucleus is split into 2 daughter nuclei to release energy.
Due to the bombardment of neutrons.
47
All nuclei have approximately the same density, what does this suggest about the SNF?
-SNF has a short range and acts of all nucleons
-The attractive nature causes nucleons to be densely packed
-Repulsion at short range stops nucleons becoming too dense
48
Why is gamma used for medical purposes?
-It has a short enough half life so that it doesn’t stay in the body for too long.
-Reducing harm to the patient.
-It is also the least ionising form of radiation.
49
Define thermal neutron
A slow moving neutron that is in thermal equilibrium with the moderator
50
Control rods example material
Boron
51
Define critical mass
The mass of fissile material needed to sustain a chain reaction
52
Define supercritical mass
The mass is greater than the critical mass so the chain reaction rapidly increases
53
Why are used fuel rods radioactive?
-Daughter nuclei produced are neutron rich
-Beta minus and gamma emitter
-Longer range
-Hot when removed from reactor
54
What is the shielding of a nuclear reactor?
multiple layers
Thick concrete to block all radiation types
Primary(Inner) layer prevents radiation getting out
Secondary(outer) layer protects against external dangers
55
State what happens to a neutron incident on the moderator
It undergoes an elastic collision
56
Describe the process of fission in a nuclear reactor
The neutron is absorbed and U-235 is formed
This causes the nucleus (in the fuel) to split into 2 smaller daughter nuclei
This realises several fast moving neutrons
57
58
Why does gamma obey inverse square law but not beta or alpha?
gamma not absorbed (1)
spreads uniformly from a point source/spherically symmetrically (1)
area over which it spreads is proportional to radius squared (1)
alpha and beta are absorbed in addition to spreading out (1)
59
Why does the shielding become radioactive in fission?
Neutrons collide with nuclei in shielding
Creating unstable isotopes
60
What is the moderator made of?
Water or graphite
61
How would you draw a binding energy per nucleon against nucleon number graph?
Initially curves up from 0 until turning point (this is the fusion section) turning point at (60,8)
Then curves down with less curvature until 220
62
Where do alpha beta minus and beta plus go on the stability curve graph?
Beta minus above
Beta plus below
Alpha below and higher up (beyond 60 on X axis)
63
Why is all the fuel in a nuclear reactor not put into a single fuel rod
neutrons need to pass through a moderator (1)
to slow them (in order to cause further fissions or prevent U-238 absorbing them) (1)
neutrons that leave the fuel rod (and pass through the moderator) are unlikely to re-enter the same fuel rod (1)
makes it easier to replace the fuel in stages
64
How exactly does closest approach method work?
At the closest approach point the alphas initial kinetic energy is fully converted to electrostatic potential
So we can find radius using electric fields equations
65
How to find ratio with gamma from source to detector
To do with areas
Area of detector / 4pi r squared
66
Define the atomic mass unit
1/12 the mass of an atom of carbon 12
67
Why is alpha more ionising
More mass more charge
68
What are two benefits of slowing down the neutrons in fission reactors
Less damage to structure
Neutrons can be absorbed by U235
