Atomic and Nuclear Physics Flashcards
1
Q
Describe the model of the atom:
A
There is a tiny, dense, positively charged nucleus at the centre of ‘empty space’ with an electron cloud
2
Q
To what order is the diameter of the atom?
A
~10^-10
3
Q
To what order is the diameter of the nucleus?
A
~10^-15
4
Q
What is the charge of a proton?
A
+1.6 x 10^-19 C
5
Q
What is the charge of a neutron?
A
0C
6
Q
What is the charge of a electron?
A
-1.6 x 10^-19 C
7
Q
How would an isotope be defined?
A
A form of an element
that has the same number of protons
but a different number of neutrons
compared to the most abundant form.
8
Q
What is the nucleon number?
A
The number of protons and neutrons in the nucleus of an atom
9
Q
A radioactive substance contains unstable nuclei. What do unstable nuclei have?
A
An inbalance of energy between the nucleons
10
Q
How does a particle become more stable?
A
By improving the balance of energy between the nucleons.
11
Q
How is the balance of energy between the nucleons improved?
A
By emitting energy from the nucleus in the form of:
- Mass
- Electromagnetic radiation (carried by photons)
12
Q
Alpha Decay is a mechanism of radioactive decay, what does it do?
A
Ejects two protons and two neutrons (as a single particle) from the nucleus
13
Q
What is Beta decay?
A
The emission of an electron from the nucleus- a neutron turns into a proton and emits an electron
14
Q
What is gamma decay?
A
The emission of high frequency (high energy) electromagnetic radiation from the nucleus
15
Q
What does ionising ability indicate?
A
How much each radiation type interacts with matter
16
Q
What is the relative charge of an alpha particle?
A
+2 (two protons)
17
Q
What is the relative charge of a beta particle?
A
-1 (one electron)
18
Q
What is the relative charge of a gamma particle?
A
0
19
Q
What is the relative mass if an alpha particle?
A
7000
20
Q
What is the relative mass of a beta particle?
A
1
21
Q
What is the relative mass of a gamma particle?
A
0
22
Q
What is the range in air for alpha radiation?
A
a few centimetres
23
Q
What is the range in air for beta radiation?
A
of the order of a metre
24
Q
What is the range in air for gamma radiation?
A
infinite
25
What is alpha radiation stopped by?
- Paper
| - Skin
26
What is beta radiation stopped by?
a few millimetres of aluminium
27
What is gamma radiation stopped by?
Many centimetres of lead or metres of concrete (sometimes combination)
28
What is the ionising ability of alpha radiation?
Very high
29
What is the ionising ability of beta radiation?
Low (medium)
30
What is the ionising ability of gamma radiation?
Very low
31
What type of process is radioactive decay?
random
32
What does a Geiger counter detect?
Emitted waves or particles from a sample
33
What does a Geiger counter display to show the radiation?
A count rate
34
What did Rutherford observe happen to alpha particles in his gold leaf experiment in 1911?
That some alpha particles went through the thin metal foil but others were scattered by large angles
35
What was Rutherfords new model?
Most the atom is empty space but there is a small, massive, positively charged nucleus in the centre of the atom with electrons orbiting around it
36
How did Rutherford's model fit in with his observations made in the experiment?
Most of the alpha particles went through the foil, so most the atom is empty space. Some alpha particles were scattered back, so there is a very small, dense, positively charged nucleus at the centre of the atom which repels the positive alpha particles
37
Compare the changes in the nucleus with alpha and beta decay
In alpha decay, the nucleus loses 4 particles, 2 protons and 2 neutrons so the nucleon number decreases by 4. In beta decay, the nucleon number remains the same as the nucleus loses 1 neutron but gains 1 proton
38
Compare gamma emission and neutron emission
In both, an uncharged particle/wave are emitted and the element remains the same. In gamma however, an electromagnetic wave is emitted and the mass of the atom stays the same. In neutron emission, a particle is emitted so the mass decreases.
39
Define irradiation
A process by which a substance is exposed to radiation (and is therefore not the actual source of radiation)
40
How can we tell if alpha radiation is being emitted by a sample?
Set up a Geiger counter so it is detecting radiation from the sample.. Put a sheet of paper between the counter and sample. If the count rate of the counter goes down, the sample is emitting alpha radiation
41
How can we tell if beta radiation is being emitted by a sample?
Set up the same process as for alpha radiation but if the count rate doesn't go down for a sheet of paper, but does go down for a sheet of aluminium, the sample is emitting beta radiation.
42
How can we tell if gamma radiation is being emitted by a sample?
If the count rate on the Geiger counter remains the same if paper and aluminum have been put between the counter and sample, the sample is emitting gamma radiation.
43
Timeline of model of atom discovery:
1897 - J.J. Thompson discovers electrons
1911 - Ernest rutherford creates nuclear model
1913 - Bohr discovers the energy levels for electrons
1924 - de Broglie establishes wave nature of electrons
1932 - Chadwick discovers the existence of the neutron
44
What does gamma radiation have a high something of?
Penetration ability
45
What are two hazards associated with handling radioactive materials?
Irradiation
| Contamination
46
What is radioactive contamination?
Particles of radioactive material left on an object
47
What kind of process is radioactive decay? Why?
Random process as it is impossible to predict which specific nuclei will undergo decay at any particular instant
48
How can patterns still emerge from the randomness of radioactive decay?
Because of the enormous numbers of radioactive nuclei presentin even a small sample
49
What is activity?
The number of decays per second
50
What is the activity of a sample dependent on?
The number of radioactive nuclei in the sample
51
What is activity measured in?
Becquerel, Bq
52
What does 1Bq represent?
One decay per second
53
What is the relationship between the activity and number of radioactive nuclei in a sample?
Directly proportional
54
Define the half-life of a substance:
the time taken for the number of radioactive nuclei in a sample to reduce by half
55
Is half-life independent or dependent of the size of the sample?
Independent
56
What is the variation between the half lives of substances?
From billions of years to billionths of a second
57
What type of decay (related to maths) is the decay of radioactive substances?
A true exponential
58
Why is the dice decay simulation a good model for the random nature of radioactive decay?
- Cannot predict when dice/atom will decay
| - Cannot predict which dice/atom will decay
59
Why do you wear gloves as a safety precaution when handling radioactive material?
- prevents contamination
| - which would cause damage/irradiation over a longer period of time
60
What is fusion?
The joining of light (low mass) nuclei to form a single more massive nucleus
61
What is fission?
The splitting of a massive nucleus to produce two or more lighter nuclei with the release of energy
62
Why is energy released from fusion?
Because there is a difference in mass between the reactants and products
63
What are the reactants in fusion?
4 protons
64
What are the products in fusion?
He-4 atom, 2 positrons, 2 electron neutrinos, gamma radiation and energy
65
How is terrestrial fusion being made possible?
-Fusion reactors are being developed that will use hydrogen isotopes (deuterium and triterium) as fuel
66
What are the advantages of terrestrial fusion over fusion in the sun?
- The fusion of deuterium and triterium is achievable at slightly lower temperatures
- It generates a higher yield (more energy output per kg of fuel)
67
What are fissile materials?
Elements which undergo fission
68
What is the most abundant form of Uranium?
Uranium-238
69
How is the proportion of fissile Uranium-235 increased?
By enriching uranium fuel
70
When does fission spontaneously occur with uranium 235?
When the minimum critical mass is reached
71
What does the spontaneous fission of uranium-235 lead to?
A chain reaction
72
What does an uncontrolled chain reaction of fission produce?
An outpouring of energy (explosion) that can be used to great destructive effect
73
What is done to initiate the fission process?
A 'thermal' neutron is fired into a Uranium-235 nucleus
74
What does Uranium-236 atom split into during fission?
Barium-144
Krypton-89
3 neutrons
(Gamma Radiation and energy)
75
What are the fuel rods in a fission reactors?
- uranium oxide in small pellets
| - enriched to about 5% Uranium-235
76
What is the purpose of the moderator and coolant (often water) in a fission reactor?
- moderator slows down neutrons to ensure successful fission events
- coolant transfers thermal energy away from the core
77
What do the control rods do in a fission reactor?
Absorb neutrons to prevent an uncontrolled chain reaction
78
What does the containment vessel in a fission reactor do?
Absorb gamma radiation from the reactor core
79
How is the coolant water used to generate electrical energy in a nuclear fission power station?
- Coolant water is used to generate steam
- The turbines convert linear k.e. of steam to particles into rotational k.e.
- Coil of wire is turned by turbines in the generator within a strong magnetic field
80
What is irradiation?
When an object or person is exposed to ionising radiation
81
What is contamination?
When an object or person has particles of radioactive material on or inside it or them
82
Does a person or object become radioactive due to irradaition?
No
83
What are the two examples of irradation?
- Radiotherapy
| - Sterlization
84
What is radiotherapy?
The irradiation of tumours to destroy cells to control growth using a powerful gamma source to produce a narrow beam of radiation
85
What is sterlised with radiation?
Food stuffs and medical equipment which cannot be sterlised at high temperatures in water
86
What are the two examples of medical contamination?
- Chemotherapy
| - Medical Tracers
87
What is chemotherapy?
The ingestion or injection of radioactive sources that target specific cells (rapidly dividing ones) and emit radiation to destroy them
88
What chemicals are typically used in chemotherapy?
Site specific ones
89
How do medical tracers work?
Radioactive material is ingested and injected to investigate digestive system or circulatory system by tracing the flow of a substance through the organs
90
What type of radiation is used in radiotherapy and why?
Gamma since it is the most penetrating ie. can penetrate skin
91
What type of radiation is used in chemotherapy and why?
Apha and Beta - less penetrating, delivers energy over a short range and does not leave the body
92
What type of radiation is used in medical tracers? Why?
Beta and gamma as they do leave the body so they can be detected externally
93
Why do radioactive materials used in tracers have a fairly short half life?
So the patient does not remain contaminated for too long
94
What are the three main industrial uses of radioactive materials?
- Pipe fractures (locating)
- Thickness control
- Level control
95
What radiation type is used in finding pipe fractures? WHy?
Gamma because it easily penetrates the ground/soil
96
What radiation type is used in thickness control and why?
Beta as the intensity of the radiation arriving at the detector would be affected by the thickness of the said material
97
What radiation type is used in level control and why?
Beta as the intensity of beta radiation arrivng at the detector drops when the level reaches required value
98
Give three ways in which a worker at a nuclear facility could become contaminated:
- absorbing radioactive particles by the skin
- breathing in radioactive particles
- entrance via an open wound
99
Why is radon a particularly harmful radioactive element?
- it is a gas at room temprature so can be inhaled
| - emits alpha radiation which is the most ionising nuclear radiation
100
How does protective clothing and a dusk mask prevent contamination?
- prevents the transfer of radioactive atoms to the worker's skin
- lungs
- and their own clothing
101
Why does taking a flight increase your radiation dose?
- cosmic rays are more intense at a higher altitude
| - at altitide there is less atmosphere above you to absorb the cosmic rays
102
How do fission products store the energy released by fission?
- as kinetic energy of the fission fragments and the (free) neutrons
103
Why does the temperature of a radioactive core increase when a large number of fission reactions occur?
- products of the fission reactions collide with other atoms in the core
- and transfer kinetic energy to these atoms
- raising the temperature
104
How do control rods affect the speed of the chain reaction?
- control rods are made of a material that absorbs neutrons
- the rods are lowered into the reactor to slow down the chain reaction
- due to the decrease in the number of neutrons produced from fission available to cause further fission
105
What is the relationship between half life and activity?
The shorter the half life, the greater the initial acitivity
106
What is the ratio of net decline?
The proportion of the radioactive element left after a certain number of half lives
107
How is gamma radiation detected from medical tracers?
using a gamma camera
108
Name natural sources of background radiation:
- radon gas
- cosmic rays
- food and drink
- radiation emitted from ground
109
What does a moderator do in a fission reactor?
It is used to slow down the emitted neutrons from the reactions so they are moving at the correct speed to cause more fission reactions
110
What is the purpose of the coolant in the fission reactor?
cools the reactor and heats water to produce high-pressure steam
111
Why is a fission reactor contained within a thick steel shell and concrete shield?
The steel is to withstand the high temperature and pressure of the core
Concrete is to absorb gamma radiation emmited by the core
112
What is meant by a chain reaction in a fission reactor?
- A series of fission reactions which are caused when
- The neutrons released from one fission go on to cause more fission reactions when absorbed by a fissionable nucleus
- which will release even more neutrons and so on
113
What would happen if the fission reactions weren't controlled by the control rods?
- Without control by the control rods, all the neutrons from each fission would go on to cause further fissions
- this would happen repeatedly and continuously so a huge amount of energy would be released rapidly in an explosion
114
Where does the energy in the form of radiation come from in a fusion reaction?
Loss of mass converted into energy
115
Why have no functioning nuclear fusion reactors been built for commercial use?
It has not been possible to create the correct fusion conditions, very high temperature and pressure, for sufficiently long periods of time
116
Why is radon harmful?
Since it is a radioactive gas which can be breathed into the lungs and produces the most ionising radition, alpha
117
What are the advantages of nuclear fuel?
- much greater supply of fuel available
- no radioactive waste produced
- helium produced (harmless, useful gas)
- most energy producing efficient process - higher yield
118
What are the disadvantages of nuclear fuel?
- very expensive to construct
- complex to operate
- very high temperatures and pressures are hard to reach and maintain
- workers have less experience of how to operate them
