6.4 Nuclear and particle physics Flashcards
1
Q
What is the proton number?
A
The number of protons inside the nucleus of a particular atom. Also known is the atomic number.
2
Q
What is the nucleon number?
A
The number is nucleons (protons and neutrons) inside the nucleus of a particluar atom. Also known as the mass number.
3
Q
What is the unified atomic mass unit?
A
1/12 of the mass of carbon-12 atom. 1 u = 1.661x10-27kg.
4
Q
What is an isotope?
A
Atoms of the same element which contain the same amount of protons but varying numbers of neutrons.
5
Q
Who was the first to propose new ideas surrounding atomic theory? What did he propose?
A
John Dalton.
He proposec elements were made of tny particles called atoms which would combine to form compounds.
6
Q
Who discovered the electron?
A
J.J. Thomson- he suggested it was like a plum pudding.
7
Q
What did J.J Thomspon discover while discovering the electron?
A
He found that a atom was 1800 times less massive than the smallest element.
8
Q
Who’s exeperiment discovered the nucleus?
A
Ernest Rutherford.
9
Q
What did Ernest Rutherfords experiment inculde?
A
He fired positivley alpha particles at a thin gold foil to see how the alpha particles were deflected- the detector was a zink sulfide screen that would produce a faint flash of light whenever an alpha particle hit it.
10
Q
What is an alpha particle?
A
Helium atoms stripped of their electrons (positively charged).
11
Q
What was the results from Ernest Rutherford’s experiement?
A
His colleagues Hans Geiger abd Ernest marsden showed most of the alpha particles past though the golf foil, however, a small numner were deflected through small angles (less than 90°) and about 1 in 8000 particles were deflected greated then 90°, causing it to bounce back in the direction it came from.
12
Q
What was deducted from Ernest Rutherford’s scattering experiment?
A
- Most of the mass in an atom is contained in a small volume called it’s nucleus.
- Nuceus has a positive charge.
- Nucear diameter is considerable smaller than the diameter of the atom, meaning most of the atom is empty space.
13
Q
Who proposed that int he nuclear model of the atom, electrons can only occupy certian orbits or energy levels around the nucleus?
A
Niels Bohr
14
Q
What did Rutherford propose after discoving the nucleus?
A
Proposed the name for proton for the positively charges particle in the nucleus in the atom. He also suspected the nucleus contained a neural particle with a mass very close to that of a proton, simce the atomic mass of most elements was arounf twice that of the elements atomic numebr.
15
Q
Who discovered the neutron? What did they show?
A
James Chadwick-he showed that the neitron has no charge and a mass very close to that of the proton.
16
Q
What is the proton number also known as?
A
The atomic number and is also denoted as the letter Z.
17
Q
What is the nucleon number also known as?
A
The mass number- often denoted as the letter A.
18
Q
What are elements with different numebers of neutrons called?
A
Isotopes?
19
Q
What defines an element?
A
It’s number of protons.
20
Q
What is strong nuclear force?
A
The force that acts between ucleons and holds the nucleus together against the electrostatic repulsion of the protons.
21
Q
What power of 10 of metres in fm?
A
x10-15m
22
Q
What is the equation for coulmbs law?
A
F= Q x q/ 4πe0r^2
23
Q
Is the value for coulmbs law in a nucleus going to be big or small?
A
Big
24
Q
What is Newtons law of gravitation?
A
F= GMm/r^2
25
Describe the graph showing strong nuclear force with distance?
* The strong force provides a repulsive force between nucleons for distances of separation up to 0.5x10-15m.
* It is attractive between distances of about 0.5x10-15m and 3x10-15m.
* Beyong the distance of separation 3x10-15m between nucleons, the strong force approaches zero, it is a **short-range force** that does not act over large distances.
26
Is the value for Newton's law of gravitation in a nucleus going to be big or small?
Small.
27
What is the force acting between protons keeping them together?
Strong nuclear force.
28
What particles does strong nuclear force act between?
Protons and neutrons
29
What happens to the strong nuclear force as you go further away from the nucleus?
It rapidly decreases with distance and does not extend much beyond adjacent protons and neutrons within the nucleus.
30
Why must the strong nuclear force become a repulsive force at a particular distance?
The strong nuclear force must bind nucleons together, but **if it was just an attractive force then the nucleons would collapse in on themselves**.
31
What does the graph look like showing how the strong nuclear force veries with distance?
32
What is the value of the strong force on nucleons inside the nucleus?
zero.
33
What happens the the stong force a nucleon experiences if it moves slightly further away to the nucleus?
It would experience a very strong force pulling it back.
34
How does the stong nuclear force keep the nucleus very stable?
Inside of nucleus, the n ucleons have a resultant force on them of zero. However, if a nucleon near the surface of the nucleus moves only slightly further away, it would have a. very large resultant force pulling back on it.
35
What are the forces on neutrons?
Since neutrons have no charge, there is no elecrical force, we can ignore the tiny gravitational forces leaving just the strong force.
36
What forces would 2 neutrons experience if they mived away from eachother?
They would experience a large force of attraction pulling them back together.
37
What forces would 2 neutrons experience if they moved closer?
They would experience a large force of repulsion which would push them back towards equilibirum.
38
What forces act on protons?
They will have an electrical force of repulsion provided by the strong force.
39
What the separation of protons be different to the separation of neutrons?
Since the size of the elecrical force on protons is much smaller than the size of strong nuclear force at this range, the separation of protons will be **almost exactly the same** as the separation of neurons.
40
What is the separation of neucleons within any nucleus independent of?
Independent of how many neucleons there are in the nucleus.
41
In comparison to the radius of an atoms nucleaus what is the radius of the whole atoms like?
The radius of the whole atom is 10,000 times greater
42
How much of the atoms mass is contained in the nucleus?
99.9% of the atoms mass
43
What should the density of an atom as a whole be like compared to the densoty to the nucleus of the atoms nucleus?
The density of the whole **should be considerably smaller** than the density of the nucleus beacuse the majority of the atoms mass is found in the nucleus which volumes tiny compared to the rest of the atom.
44
What happens to the volume and nuclear radius as more protons and neutrons are added to a nucleus?
The volume and the nuclear volume will increase.
45
What does the graph look like of nuclear radius size against neucloen number look like?
46
What is the relationship between nuclear radius and nucleon number?
R=r0A^1/3
Where R= nuclear radius, r0= constant, A= nucleon number
47
What is the nuclear radius directly proportional to?
The cube root of the mass number.
48
What is the constant r0?
r0 is the value of R when A=1 (the size of the hydrogen nucleus radius)
49
Describe the graph R against A^1/3?
Will get a linear relationship and the gradient of the graph will be equal to the constant r0.
50
What is the value of the constant r0?
1.4x10^-15 or 1.4fm
51
What equation relates the radius of a nucleus to its mass number?
R=r0A^1/3
52
How can you simplify the equation R=r0A^1/3 to make A a whole value?
Raise both sides to the power of 3 to obtain R^3=r0^3A
53
What is an α-particle?
A particle comprising 2 protons and 2 neutrons ejected from the nucleus during radioactive decay. It's identical to a helium nucleus and is emitted due to it's unusually high stability as a particle.
54
What is a β-particle?
It's a high-speed electron emitted from the nucleus during beta decay. It is produced when a neutron changes into a proton.
55
What is a γ-ray?
A form of elecromagnetic wave with wavelengths between 10^-16 and 10^-9. Emitted from the nucleus during gamma decay.
56
What is radioactive decay?
Radioactive decay is the spontaneous and random decay od an unstable nucleus into a more stable nucleus by the emission of alpha, beta and gamma radiation.
57
Why is radioactive decay described as being spontaneous?
It happens without being affected by any external factors such as temperture or pressure, or by chemical reactions or placing it in a electric or magnetic field.
58
Why is radioacitive decay described as random?
It is not possible to determine exactly how many particles will decay each second, nor which ones will decay or when a particular nucleus will decay.
59
How was radioacitivty initially detected?
It was first detected by the darkening of a photographic film or plate. Soon after this, the material zinc sulfide started to be used. **Zink sulfide gives out faint flashes of light when alpha particles are incident on it,** enabling actual counts to be made of how much radiation was being emitted.
60
What did Hans Geiger invent?
He invented the Geiger-Muller tube which detencts ionisation of gas molecules caused by radioactive decay.
61
What will stop the penetration of apha particles?
A few centimetres of air or a sheet of paper.
62
What would stop the penetration of beta particles?
Beta particles will travel through a few meters of air and be stopped by thin aluminium.
63
What would stop the penetration of gamma rays?
Gamma rays will penetrate both parer and aluminium but will stopped by thick lead.
64
When passed through an electric field, how do alpha particles act?
Alpha particles would move in the direction of the magnetic field, towards the negative plate and so have a positive charge.
65
When passed through an electric field, how do beta particles act?
Beta particles move in the opposite direction of the elctric fiels, so have a positive charge.
66
When passed through an electric field, how do gamma rays act?
Gamma rays were not defelected since gamma radiation is composed of photons and is uncharged.
67
What are the main properties of alpha particles? (Nature, mass, charge, typical speed of emission)
* Nature: helium nucleaus: 2 protons, 2 neutrons
* Mass/u: 4
* Charge: +2e
* Typical speed of emission: 5% of speed of light: 0.05c
68
What are the main properties of beta minus particles? (Nature, mass, charge, typical speed of emission)
* Nature: electron
* Mass: 1/1840 u
* Charge: -e
* Typical speed of emission: 99% of the speed of light
69
What are the main properties of beta-plus particles? (Nature, mass, charge, typical speed of emission)
Nauture: Positron
Mass: 1/1840 u
Charge: -e
Typical speed of emission: 99% of the speed of light
70
What are the main properties of alpha gamma rays? (Nature, mass, charge, typical speed of emission)
* Nature: electromagnetic radiation
* Mass: 0
* Charge: 0
* Typical speed of emission: speed of light
71
What investigation is done to investigate the absorbtion of alpha-particles, beta-particles and gamma rays?
Using a Geiger Muller tube and counter to detect the radiation passing through sheets of different materials placed between the tube and the radiative source.
The background radition count rate (amount of inonising evens detected per second/ per minute when no radiation source is nearby) is subtracted from all recorded count rates.
Use paper and aluminium foils and pieces of lead of different thivknesses to investigate what thickness to investigate what thickness of each material stops each type of radiation.
72
What is beta-minus decay?
In beta-minus decay in a neutron in the nucleus breaks down into a proton under thee influence the of weak nuclear force, and a beta-minus particle and an electron antineutrino are emitted. A beta-minus particle is positron.
73
What beta-plus decay?
In beta-plus decay, a proton in the nucleus breaks down into a neutron under the influsence of the weak nuceur force, and a beta-plus particle and an electron neutrino are emitted. A beta-plus particle is a positron.
74
When nuclei undergo radioacitive decay, what must be conserved?
Both the number of particles and the total charge must be conserved.
75
What is an alpha particle?
An alpha paricle in a fast-moving helium nucleus.
76
What is an alpha particle composed of?
Since it is a fast moving helium atoms, it is composed of 2 protons and 2 neutrons.
77
What happens to an element when it undergoes alpha decay?
Since an element is defined to its atomic number, the nucleus will become that of another element.
78
What is responsible for both types on beta decay?
The weak nuclear force.
79
Describe what happens in the nucleus during beta-minus deacy.
A neutron in the nucleus of an atom changes to a proton, and an elecrton and and electron antineutrino are released from the nucleus. This electron that is ejected is the beta-minus particle.
80
When does beta-minus decay occur?
Beta-minus decay occurs in nuclei that are unstable, low in mass and have too many neutrons relative to the zone of stability.
81
How is charge conserved when beta-minus decay occurs?
Since the beta-minus is an elecron, it has a mass of nearly 0 and a charge of -1. **To conserve total charge the atomic number of the radioacive nucleus that is decaying will increase by one. The mass number does not change**.
82
What is an example of beta-minus decay?
The decay of carbon-14 to nitrogen-14 with the emission of an electron and an antineutriono.
83
What is the quark transformation of beta-minus decay?
A down (d) quark changes to an up (u) quark.
84
Describe what happens in beta-plus decay?
Beta-plus decay occurs when a proton within a nucleus turns into a neutron. This results in the ejection of a positron and a neutrino from the nucleus.
85
When does beta-plus decay occur?
Beta-plus emission occurs in nuclei where are too many protons compared to the number of neutrons , relative to the zone of stability.
86
What is an exaple of beta-plus decay?
When of flouride-18 into oxygen-18 with the emission of a positron and an elecrton nutrino.
87
What is the quark transformation of beta-plus decay?
An up quark changes to a down quark
88
What happens during gamma radiation?
Gamma radition is frequently accompanies alpha or beta decay, but never occurs purley gamma radiation.
89
What is an example of gamma radiation?
When colbolt-60 undergoes beta-minus decay. The colbolt-60 source will emit an electron and then 2 gamma photons before becomeing a more stable isotope nickel-60.
90
What does the emission of gamma rays lead to?
It leads to a more energetically stable nucleus without a the change in mass number or change.
91
What does the graph showing the number of neutrons plotted against the number of protons for stable isotopes show?
The graph shows as the atomic number increases, there are relatively more neutrons the=an protons in a stable nucleus.
92
What does the zone of stability show?
Shows the region where stable nuclei are found.
93
What does the zone of stability do an the line N=Z (neutrons=protons) as the nuclei get heavier?
The zone of stability curve diverges from the line N=Z.
94
What will unstable nuclei do in order to get closer to the zone of stability?
Unstable nuclei will emit beta-minus, beta plus or alpha particles to get closer to the zone of stability.
95
How to alpha, beta and gamma raditation behave in a magnetic feild?
Moving charges are deflected in a magnetic field (provided the direction of movement is perpendicular to the
field direction). Gamma rays are uncharged so would not be deflected. Alpha and beta particles have opposite
charge, so would be deflected in opposite directions.
The radius of the curved path depends on the mass, speed and charge of the particle ቀݎ ൌ ௩
ொቁ. Alpha particles
are much more massive, so would generally be deflected into a path with a larger radius (difference in speed or
in charge is not as great as difference in mass). However, speed of emission depends on the source so there is no
strict rule about which is deflected more.
96
When investigating the absorbtion of alpha, beta and gamma raditation by different thicknesses of materials, why is it best to record the counts over a long period of time anf take the mean count per minute?
Radioactive decay is random and it is impossible to predict when a particular nucleus will decay. By recording
the count over a long period of time it is possible to calculate and compare a mean number of counts per minute,
which will be more accurate. Also, the background count fluctuates randomly over time, so recording over a
long period of time smooths out random variations of the background count.
97
What precausions can be done to protect yourself from radioactive souces?
Minimise time of exposure, increase distance from their body to the radioactive source (e.g. by using tongs),
shield sources when not in use, such as in a lead-lined box. Avoid direct contamination of hands and clothing by
using tongs to handle specimens and/or gloves and other protective clothing.
98
What methord could you use to identify what types of radiation are being emitted by a source?
Place the Geiger counter detector a fixed distance (less than 5 cm) from the source. In turn, place a sheet of paper
then a thin sheet of aluminium between the source and the detector. Compare the mean count rate for each
absorbing material.
If the count rate drops to zero when the sheet of paper is placed between the source and detector, the source
emits only alpha particles. If the count rate is not reduced by the sheet of paper, the source is not an alpha
emitter. If the count rate is reduced but not zero when the sheet of paper is placed between the source and
detector, the source emits alpha particles but also either beta or gamma radiation.
If the count rate drops to zero when the sheet of aluminium is placed between the source and detector, the source
emits beta particles but not gamma rays. If the count rate is reduced but not zero when the sheet of aluminium is
placed between the source and detector, the source emits beta particles but also gamma rays.
99
What are fundamental particles?
Particles that cannot be broken down into smaller components.
100
What are hadrons?
Particles consisting of a combination of quarks to give a net zero or whole number charge. Neutrons and protons are hadrons.
101
What are leptons?
Leptons are fundamental particles; electrons and neutrinos are leptons.
102
What are quarks?
Quarks are components of hadrons, and have a fractional electric charge. They are fundamental particles. There are different types of quarks, e.g. up, down and stange quarks.
103
What is a neutrino?
A neutrino is a fundamental particle (lepton) with almost no mass and zero charge. Each neutrino had an antimatter partner called an antineutrino.
104
What is the weak nuclear force?
The weak nuclear force is felt by both quarks and leptons. It can change quarks from one type of lepton from one type of another and responsible for beta-decay.
105
What is an anitparticle?
A particle of anitmatter has the same mass bur, if charged, the equal and opposite charge to its sorrisponding particle.
106
What are the 2 categories of subatomic particles?
Hadrons and leptons
107
What are hadrons composed of?
Quarks
108
Can quarks be broken dwn into smaller constituents?
No, so they are fundamental particles.
109
What are some examples of hadrons?
Protons and neutrons- they both are composed for 3 quarks.
110
What do all hadrons experience?
The strong nuclear force.
111
Are Leptons fundamental particles?
Yes
112
Give an example of a lepton.
An electron
113
hat does each lepton have?
Each lepton has it's own neutrino which is also fundamental.
114
What forces do leptons experience?
All leptons experience the weak nuclear force, but do n not experience the strong nuclear force.
115
What is a protons antiparticle?
An antiproton.
116
What is an electrons antiparticle?
A positron
117
What is thr charge on an antiparticle?
The antiparticle is opposite in charge to the particle itself.
118
What makes an antineutron possible even through neutrons have no charge?
How they are constructed is different- the quarks are composed of give a net charge of zero in each case, but an antineutron is **composed of antiquarks**, not quarks.
A neutron and antineutron are distinguishable from one another becuase neutrons and antineutrons annihilate each other upon contact.
119
What happens as mass collides with antimass?
Annihilation occurs as their combined mass is converted into energy.
120
What hppens when a protons collides with an antiproton?
They would both be annihilated and their masses converted to energy in the form of photons.
121
What were the 3 quarks initially proposed?
* Up
* Down
* Strange
122
What does a line placed over the top of a quark indicate?
It's an antiquark.
123
What is an antiquark?
Antiquarks are similar to theor quark partner but have the opposite charge anf are composed of antimatter.
124
What is the symbol, charge, strangness and bayron number of an up quarks?
* Symbol: u
* Charge: +2/3e
* Strangeness: 0
* Baryon number: 1/3
125
What is the symbol, charge, strangness and bayron number of a down quark?
* Symbol: d
* Charge: -1/3e
* Strangeness: 0
* Baryon number: 1/3
126
What is the symbol, charge, strangness and bayron number of a strange quark?
* Symbol: s
* Charge: -1/3e
* Strangeness: -1
* Baryon number: 1/3
127
What is the symbol, charge, strangness and bayron number of an anti-up quark?
* Symbol: u (with a line over the top)
* Charge: -2/3e
* Strangeness: 0
* Baryon: -1/3
128
What is the symbol, charge, strangness and bayron number of an anti-down quark?
Symbol: d (with a line over the top)
Charge: +1/3e
Strangeness: 0
Baryon number: -1/3
129
What is the symbol, charge, strangness and bayron number of an anti-strange quark?
* Symbol: s (with a line over the top)
* Charge: +1/3e
* Strangeness: +1
* Baryone number: -1/3
130
What quarks are protons constucted of?
uud (2/3 + 2/3 - 1/3)e
131
What quarks are neutrons constructed of?
udd (2/3 - 1/3 - 1/3)e
132
What hadron is this?
Proton
133
What hadron is this?
Neutron
134
Define radioactive actitivty?
Activity is the number of nuclear decays per unit time. The activity of one decay per second is called one bacquerel (Bq).
135
What is the decay constant?
λ, is the **probability that an individual nucleus will decay per unit time**, Given by V=A/N, and has the same dimentios as time. Units are s^-1.
136
What is half life?
t1/2, is defined as the mean time taken for the activity of a source, or the number of undecayed nuclei present to halve.
137
Over time, what will happen to the actitivity of the sample?
The samples activity will decrease as there are fewer unstable nuclei left to decay.
138
What is the activity related to?
The activity is related to:
* The umber of undecayed nuclei.
* The probability of those nuclei decaying each second.
139
What word describes the probability that a particular nucleus will decay each second?
The decay constant.
140
What is the activity of a source directly ptoportional to at any time?
Proportional to the number of undecayed nuclei present:
A=λN
141
* What does the equation A=A0e^-λt show??
Shows that the activity of a radioacitive source decreases exponentially with the same decay sonstant.
142
What does the equation N=N0e^-λt show?
Shows the number of undevcayed nucei of a radiosactive source decreases exponentially with the same decay constant.
143
Why does the line show variation in activity in the graph of activity against time for a radioacitive source?
Background radiation causes variation to be seen in the graph.
144
What will happen to a source with a large decay constant?
There is a high probability of its nuclei decaying and so it will take a short time for all the unstable nuclei to decay and the activity or number of undecayed nuclei to fall to zero.
145
What will happen to a source if the decay constant is small?
The likelihood od an individual nucleus decaying is small and it will take a long time for the substance to stop being radioactive.
146
What does t1/2 mean?
Half life.
147
What graph can half life be estimated from?
Half life can be estimated from a graph of number of particles against time or a graph of the corrected count rate.
148
What graph can half life be estimated from?
Half life can be estimated from a graph of number of particles against time or a graph of the corrected count rate.
149
For every half life that passes, how will the intensity of the radioacitve source change?
It will decerase by 50%
150
From the equation A=A0e^-λt what is the equation for t?
t=ln(A/A0)/λ
151
What does the equation t=ln(A/A0)/λ show?
This shows that the **equal intervals of time give equal fractional changes in the acitivity**. The half life is constant.
152
What is does a graph showing half life look like?
153
Using A=A0e-λt what will A equal after one half-life? t=t1/2.
A=1/2A0
154
What equation is formed when A=1/2A0 into A=A0e^λt1/2? (A after 1 half life)
* 1/2A0=A0e^λt1/2
* 1/2=e^λt1/2
* **ln2=λt1/2**
155
What does the equation ln2=λt1/2 show?
Note that if the units for t1/2= mins and the units for λ=m^-1.
The equation shows that the **half life** of a radioactive source is **inversely proportional** to it's **decay constant**.
156
What is the equation for the decay constant?
λ=A/N'
* N=number of undecayed nuclei
* A=acitivity
157
What does the slope of a tangent show?
∆N/∆t
158
How can you find the decay constsnt and the half life from this graph?
* From ∆N/∆t=-λN we can find the decay constant λ by finding the gradient at any point. The half-life can then be found from ln2=λt1/2.
* Alternatively, graphic methords usued a logarithmic plot. From A=A0e^-λt, if we rearrange and take natural logs, we get: lnA0=LnA-λt. A graph of lnA against t should be a straight line, of gradient -λ.
159
Define annihilation.
Annhilation is the process in which a paticle and it's antiparticle interact and their combined mass is converted into energy via E=mc^2.
160
Define pair production.
The prcess of creating a particle-antiparticle pair from a high energy photon.
161
What is the mass defect?
The mass defect is the difference in mass of a nucleus and the tootal mass of its separated nucleons.
162
What is binding energy?
The binding energy of a nucleus is the minimum energy required to separate the nucleus (protons and neutrons) into its consitiuent parts.
163
In radioactive decay, how is energy released?
Energy is released in the form of kinetic energy of the fast moveing alpha or beta particles, and may be released as gamma ray photons.
164
What is the orgin of the energy released in radioactive decay?
The origin of this energy is the conservation of some of the masses of the particles involved to energy.
165
What did Eistein show happened to a particles mass as it's speed increses?
As a partciles speed increases, it's mass increases.
166
What does Eisteins principle of the equivalence of energy and mass state?
It states that if energy is supplied to or rempved from an object, it's mass changes by an equivalent amount.
167
What is the equation that shows Eisteins principle of the equivalence of energy and mass?
E=mc^2
168
What does the equation E=mc^2 show?
Eisteins principle of the equivalence of energy and mass.
169
What does Eisteins principle of the equivalence of energy and mass show?
When energy is removed there is an invreases in mass, and when there is a decrease in the mass of a system, an amount of energy equivalent to the change in mass is released. The **total amount of mass-energy is conserved**.
170
Regarding the equation E=mc^2, what units are used when working with nulei?
* Mass units- the unified mass constant u= 1.6605x10^-27kg
* Energy units- electron volt eV
171
A particle and an antiparticle are annihilated when they meet. What is the opposite that can occur?
A burst of electromagnetic radiation from annihilation of a particle-antiparticle pair can result in the creation of a new pair od particles (**pair production**).
172
What is a mass spectrometer used for?
Determining the mass of particles very accuratly.
173
What is observed when the mass of a given nucleus is compared with the maass of its consitiuent nucleons?
The total mass of the separated nucleons is always greater than the mass of the nucleus. The **extra mass is called the mass defect**.
174
What does the difference in mass between the mass of the separate nucleons and the mass of the nucleus come from?
It comes from the fact that they are all held together by the strong nucleur force.
175
Explain why the facts that all the nucleons being bound together by the strong nuclear force explains the mass defect.
As they are all held togther by the stong nuclear force, **work has to be done** to separate the nucleons, so the separtated **nucleons gain potential energy** and by **Eisteins mass-energy equation** they then have **more mass**.
176
Whaat is the minimum energy needed to break up the nucleus into its consituent nucleons called?
The binding energy of the nucleus.
177
what must you remeber when dealing with the binding energy of the nucleus?
The binding energy is not the energy holding the nucleus togteher.
178
What determines how great the binding energy is of a nucleus?
How many nucleons there are in a nucleus.
179
Will the binding energy be greater in a uranium nucleus or a iron nucleus? Why?
The binding energy of a uranium nucleus will be greater than that of an iron nucleus since there are more nucleons to separate.
180
How do we work out the binding energy per nucleon of a nucleus?
Divide the total binding energy of a nucleus by the number of nucleons.
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Regarding the binding energy per nucleon in a nucleus, how can we tell how stable a nucleus is?
The greater the binding energy is **per nucleon,** the more stable the nucleus wiill be.
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What is a key differnce between the binding energy of a nucleus and the binding energy er nucleon in its nucleus?
The value of the binding energy of a nucleus does not tell us how stable a nucleus is, whereas, the binding energy per nucleon does.
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What does the graph of binding energy per nucleon plotted plotted against nucleon number look like?
184
What does this graph show?
It shows that the nuclei of low and high nucleon number have smaller binding energy of those nuclei with a nucleon number of about 56.
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Using the graph, what will happen when 2 low nucleon number elements combine to a higher nucleon number element (nuclear fusion?
This will result in the release of energy.
186
Using the graph, what will happen when a heavy nucleus is split into 2 lighter nuclei? (nuclear fission)
It will release energy.
187
Using the graph, what is similar between nucleau fusion and nucear fission?
After nuclear fission and nuclear fusion, energy will be released feom both.
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What is induced nuclear fission?
It occurs whern a **nucleus absorbs a slow moving neutrons** and the resulting unstable nucleus undergoes a **fission reaction** to split into **2 smaller nuclei** and a small number of neurtonas, relesing energy.
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Define a chain reaction?
A chain reaction is the **sequence of nuclear reactions** produced when an **induced nuclear fission reaction triggers** more than one further fission reaction.
190
What is a control rod?
A rod that can be lowered into the core of a neclear reactor, **absorb neutrons and slow down the chain reaction**. Control rods are normally made of **boron**.
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What is a moderator?
| Nuclear fission
A moderator is a substance used in a nuclear reactor which **slows down neutrons** so that they have a greater chance of being absorbed by the fissile nuclear fuel. The moderater is usually made of **graphite.**
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What does the word fission mean?
Splitting up or breaking into parts.
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Can spontaneous fission occur?
In some naturally occuring isotapes of heavier elements such as uranium will undergo spontaneous fission. This is rare.
194
Wht causes induced nuclear fission?
The absorption of a slow-moving neutron.
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What is released in nuclear fission?
More neutrons and an enormous amount of energy.
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Howw is nuclear fission used in nuclear power stations?
nergy released heats water into steam, which is then blown onto turbines at high ppressure. The roation of the turbines turns a generator to produce electricity.
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What happens when a nucleus absorbs another neutron in fission?
It makes the nucleus **unstable** which quickly disintigrates inton 2 **unequal fragments**, in which may decay into other fragments.
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In what form of energy is energy released in fission?
Kinetic energy in the fission fragments and neutrons.
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How does fission release energy?
The 2 fission fragments have a greater binding energy per nucleon. Mass-energy is conserved so the energy release can be found by E=mc^2.
200
How does a nuclear reactor control the fission chain reaction?
It ensured that on average only **one of the neutrons produced by the fission** of uranium-235 causes susequent fission.
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What absorbs extra nuetons in a nuclear reactor?
Control rods.
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How do control rods control a fission chain reacion in a nuclear reactor?
The rods are moved in or out of the reactor, controlling the rate of eperation of the chain reaction.
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What are control rods often made of?
Boron.
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When does nuclear fusion occur?
When smaller nuclei join together to produce heavier nuclei.
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How is energy released during a fusion reaction? (Binding energy)
* The resulting nuclei have a **binding energy per nucleon that is greater** than than the combined binding energy of the individual nuclei that have fused together. The **difference in binding energy is released as kinetic energy** of the resulting particles as **photons**.
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How is energy released during fusion? (change in mass)
The nucleus appears to loose mass, which results in energy being released. Mass-energy is conserved.
207
What fusion reactions occurs in stars?
The reaction between 2 **deutrons**, which are the **nuclei of an isotpe of hydrogen** called **deuterium** and compise one proton and one neuton?
208
What is the problem of fusion of 2 deuterons?
The reaxtion requires 3.6Mev per reaction. The** 2 deuterons repel** one another very strongly at close range due to **electrostatic repulsion**, so they will not normally fuse. Temperatures as high as **10 000 000 K** are needed, so that the nuclei have a great **kinetic energy **and aproach close enough to experince the **attractive strong nuclear force**.
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What sort of neutrino does B-minus decay produce?
An anti neutrino
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What sort of neutrino does B-plus produce?
Neutrino
211
What are the advantages if we can do fusion on earth?
* No radioactive waste products formed
* There is unlimited supply of raw materials. About 1% of seawater molecules have a deuterium artom in them.
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Why can fusion reactions not be done on earth?
At present, any apparatus that can induce fusion requires more electricity than it can produce.
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What devise can provide the temperatures needed for fusion?
Tokamak devices
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What is a tokamak device?
A device that can provide temperatures need for fusion.
215
How can a tokamak device create fusion?
A huge discharge through a deuterium-trirum gas mixture from a bank of capacitors is compressed by magnetic feilds into a dougnhut shped ring, within temperatrures of a hundred million degrees can be mintined for a few miliseconds.
