Nuclear Physics Flashcards
(68 cards)
1
Q
who proposed the plum pudding model
what did the model look like
A
- jj Thompson
- a spherical ball of positive charge with electron scattered evenly throughout
2
Q
what did jhon dalton propose
A
- Atoms are smallest constituents of matter
- Elements are made of identical atoms
- When chemical reaction take place atoms rearrange to make different substances
3
Q
what was the gold foil experiment
who did the experiment
A
- positively charged alpha particles fired at thin gold foil
- Ernest Rutherford
4
Q
what where the key takeaways from the gold foil experiment
A
- Atoms are mostly empty space
- Centre of atom is very small
- Nucleus of atoms are very dense because they can deflect fast moving alpha particles
5
Q
who came up with the ‘planetary model of the atom’
what did the model entire
A
- Niels Bohr
- electron orbit the nucleus in shells or energy levels
6
Q
who discovered Nuetrons and when
A
James Chadwick 1932
7
Q
what was the order in which discovers about the atom took place
A
Dalton
Thompson
Rutherford
Quantum mechanical model
8
Q
what is radiation
A
when an unstable nucleus releases energy in the form of EM waves or Subatomic particles in order to become more stable
9
Q
Name all three radiation
what is there range and ionising strength
A
- Gamma, Alpha, Beta
Range: infinite, 2-10 cm, 1 m
ionising: very weakly, weakly, highly
10
Q
how do you find the type of radiation a source is emitting
A
- Find background count rate (take readings on Giger muller tube three times and then calculate a mean)
- place radioactive source infront of Geiger muller tube and place paper, aluminum foil and lead between source and tube.
- find material where count rate decreases the most, accounting for background
11
Q
what uses does Gamma radiation have
A
- Steel sheets
- medical detector
- radiation therapy
- sterilize equipment
12
Q
what can radiation monitor the thickness of
A
Alpha: paper
Beta: aluminum foil
Gamma: steel sheets
13
Q
how are gamma rays used in radiation therapy and as a medical detector
A
- As a detector: Gamma has a short half-life and is very lowly ionizing therefore can be injected into a patient and they can be diagnosed with cameras that detect gamma rays
- In radiation therapy: Sources of gamma are focused on a particular tuma they can kill it however they also kill healthy cell
- Sterilize equipment: Gamma can kill bacteria
14
Q
how is intensity of gamma mapped over given distance
A
inverse square law
15
Q
how do you investigate the inverse square law
A
- measure count rate at regular distance intervals away from a gamma source
- Make sure to account for background
- Plot graph of I against 1/x2
- the gradient will be constant
16
Q
How can all three types of radiation cause harm to our bodys
A
- Alpha - only when ingested it will be incredibly dangerous and high ionizing
- Beta - less ionizing however contact could be dangerous
- Gamma - prolonged exposure could cause mutation and damage to cells
17
Q
what is equation for corrected count rate
A
Corrected count rate = Total count rate - Background count rate
18
Q
when investigating radiation what safty measure should you take
A
- handle with long tongs
- store in lead lined box
- warning signs
- never point source at anyone
19
Q
what are sources and examples of background radiation
A
- Radon gas - released from rocks
- Artificial sources
- Cosmic rays
- Rocks
20
Q
what rock release radon gas
A
granite and limestone
21
Q
what are examples of artificial sources of radiation
A
medical equipment
nuclear weapons testing
decaying nuclear waste
22
Q
what can be said about the process of radioactive decay
A
- Random therefore cannot be predicted
- when specific nuclei decay however the decay can be modelled by the exponential function
23
Q
what is the decay constant
A
probability of a nuclei decaying per second or per unit time
24
Q
what is activity defined as
A
- the average number of nuclei that decay per unit time
- activity is measure in Bq
25
what is the equation specific to the Number of nuclei against time graph
-λN
26
what are the exponential decay equations
A = Ae^-λt
N = Ne^-λt
C = Ce^-λt
27
how can you tell if a variable can be modelled by exponential decay
if it is proportional to the activity
28
what is a halflife
average time taken for number of nuclei to fall to half its original value
29
when is carbon dating deemed as reliable
between 500 - 6000 years
<500 then change in carbon atoms are negligible
>6000 carbon atoms will of decayed to background levels
30
under what condition will a nuclei decay
when the strong force and electrostatic force are not equal
31
in heavier element why is there an imbalance in proton to neutron ratio
- More Protons increase the electrostatic force of repulsion therefore more neutrons are needed to keep the protons apart
- Neutrons also increase binding/strong force therefore counteracting electrostatic force
32
how can you estimate nuclear radius of an atom
Using the distance of closest approach method or electron diffraction
33
what is the distance of closest approach method
what is the equation
- The distance a charged particle reaches before it is repelled by the nucleus (Ep = Ek)
Ep = Ek = Qq/4πε0r
34
what is permittivity of free space
constant which represents the capability of an electric field to permeate a vacuum
35
what is the draw back of distance of closest approach method
overestimate
36
How is electron diffraction used to estimate nuclear radius
- Electrons fired at high speeds so there de Broglie wavelength is x10^-15 and directed through a crystal lattice causing them to diffract
- This creates a circular diffraction patter
by plotting graph of intensity vs diffraction angle you can find equation:
sinθ = 0.61λ/R θ- angle of fist minimum
λ- wavelength of electron
R- radius of nucleus
37
what can be derived from nuclear radius vs nucleon number graph
R = R0A^1/3
R∝A^1/3
38
does nuclear density change
no
39
what is the equation linking mass and energy
e = mc^2
40
what is the mass defect
- measuring the mass of a nucleon vs the mass of its constituent parts the mass of the nucleon is always lower, this is because nucleons transfer energy to surroundings in the form of mass
41
what is Nuclear Fission
- Splitting of very large nuclei into two daughter nuclei
- this releases at least 1other neutron and energy
- this is because the two daughter nuclei have greater binding energy therefore release more energy when formed
42
what is nuclear fusion
- two smaller nuclei join together to form one large nuclei
- energy is released because the large nucleus has a much higher binding energy
43
what is the condition for nuclear fusion to take place
- nuclear fusion will only take place under extreme temperatures and pressure to overcome the electrostatic force of repulsion between nuclei
44
what is binding energy
energy needed to break a nucleus down into constituent parts
45
what is the benefit of nuclear fission power plants
- generates minimal greenhouse gasses
- operational all the time
- efficient energy production
46
what are the risks of nuclear power
- daughter nuclei are radioactive
- meltdowns are disastrous
- nuclear waste can be expensive or difficult to dispose of
47
what is a thermal nuetron
neutrons with energy low enough to be absorbed by nucleuses
48
what is the process of induced fission
when a thermal neutron is fired at uranium 235 nucleus causing it to undergo fission and release energy and at least 1 other neutron
49
what is a chain reaction
neutrons from 1 fission go on to cause at least 1 more fission
50
what is the critical mass
minimum fuel to sustain a steady reaction
51
what is a moderator
a moderator slows down fast neutrons through elastic collisions.
this allows the neutrons to be absorbed increasing the likely hood of more fission reactions
52
what should moderator have in common with neutrons
what materials are usually used
moderator atoms should be close in size to neutrons to allow for elastic collisions
water
53
what do control rods do
what properties to control rods have
what materials are control rods made out of
- absorb neutrons to control rate of fission
- boron, cadmium
- they need to be able to absorb neutrons without decaying or undergoing fission
54
what is the purpose of a coolent in a nuclear reactor
absorb heat, uses heat to produce steam therefore electricity
55
what properties should coolant material have
- high specific heat capacity
- high boiling point
56
what materials are coolents made out of
water, molton salt, helium
57
how do fuel rods keep reaction under control
95% Ur 238 which does not undergo fission therefore help to absorb neutrons
58
what is the process of enrichment
uranium extracted from the ground has 99% Ur 238. this has to be brought to 95% Ur 238 and 5% Ur 235 in order to be suitible for fission
59
what is an emergancy shut down
control rods are dropped into reactor to stop reaction immediately
60
what level waste are spent fuel rods
high level wast
61
how do you dispose of spent nuclear fuel rods
- removed remotely and placed in cooling ponds close to reactor site
- remain in cooling ponds for up to 1 year
- Any remaining plutonium or Ur 235 is removed and recycled
- rods are then vitrified (encased in glass)
- waste contained in thick steel casks and buried in deep caverns to limit change of contamination
62
how efficient is nuclear power
1 kg uranium = 25 kg coal
63
what are applications of radioactivity
Nuclear power
nuclear weapons
Uranium lead dating
Carbon dating
Medicine`
64
describe carbon dating
- all living organisms have constant value of carbon 14 atoms
- when they die carbon 14 decays with a half life of 5730 years
- when organisms die the levels of carbon 14 can be tested against original level to estimate age
65
what is the zone of stability
Graph of neutron number against proton number the region where stable nuclei inhibit is the zone of stability
66
how is Neutron vs proton number graph constructed
Zone of stability: straight line up to (20,20)
to the left of zone is B-
to the right of zone is B+
top right of zone is Alpha and fission
67
describe graph of binding energy per nucleon against the number of nucleons
peak is at iron(56) just above 8 MeV's
for atoms bigger than iron fission takes place
for atoms smaller the iron fusion takes place
68
what is the purpose of concrete around a reactor
what can happen to this concrete over time
to block radiation from harming workers
concrete can become radioactive due to neutrons and other material therefore it decays via beta -
