8A. and she like a model, oh woah [COMPLETE] Flashcards
nuclear & particle physics (nuclear) (128 cards)
1
Q
What is the nucleon/mass number?
A
The total number of protons and neutrons in the nucleus
2
Q
What is the proton/atomic number?
A
The total number of protons in the nucleus.
3
Q
What is an isotope?
A
An isotope is an atom of the same element that has an equal number of protons but a different number of neutrons.
4
Q
What are the isotopes of hydrogen?
A
Protium (normal), deuterium, and tritium.
5
Q
What is the simple experimental set up for alpha particle scattering?
A
Alpha particles fired at thin gold foil and a detector on the other side to detect how many particles deflected at different angles.
6
Q
What are alpha particles?
A
The nucleus of a helium atom and is positively charged.
7
Q
What is the charge of an alpha particle?
A
+2
8
Q
What are the observations from the alpha particle scattering experiment?
A
- Majority went straight through without deflection.
- Some were deflected at small angles less than 10°.
- Only a small number were deflected straight back at angles of greater than 90°.
9
Q
What deductions can be made when the alpha particles went straight through the gold foil?
A
It suggested that atoms are mainly made up of empty space.
10
Q
What deductions can be made when the alpha particles were deflected at angles <10°?
A
This suggested there is a positive nucleus at the centre as two positive charges would repel.
11
Q
What deductions can be made when the alpha particles were deflected back at angles >90°?
A
This suggested the nucleus is extremely small and where the mass and charge of the atom is concentrated. Therefore, atoms consist of small dense positively charged nuclei.
12
Q
What was Dalton’s model of atomic structure?
A
- Billard ball model.
- All matter were made of tiny solid particles called atoms.
- Atoms were the smallest constituent of matter and cannot be broken down any further.
- Atoms of the given element are identical to each other. Atoms of different elements are different to each other.
- When chemical reactions occur, the atoms rearrange to make different substances.
13
Q
What was Thomson’s model of atomic structure?
A
- He discovered the electron.
- Plum pudding model.
- Atoms contain positive and negative charges in equal amounts so overall is neutral.
- The atom was modelled as spheres of positive charge with uniformly distributed charge and density. The negatively charged electrons were stuck onto the sphere like in a plum pudding.
14
Q
What was Rutherford’s model of atomic structure?
A
- Planetary model of atom.
- Atoms have a central, positively charged nucleus with the majority of the mass. Electrons orbit the nucleus like planets around a star.
15
Q
What was Bohr’s model of atomic structure?
A
- Improvement of the planetary model.
- Electrons occupy shells or energy levels around the nucleus at particular distances from the nucleus.
16
Q
What is the quantum mechanical model of atomic structure?
A
The likelihood of finding an electron in a certain position.
- Nucleus surrounded by electron clouds. If the cloud is dense, there is a greater chance of finding an electron there.
- The neutron was later discovered.
17
Q
What is thermionic emission?
A
When an electron gains enough energy from heat and is able to leave the surface of a metal.
18
Q
What is the difference between thermionic emissions and photoelectric effect?
A
Energy absorbed by electrons are thermal energy rather than photons.
19
Q
What can we do to the electrons once they are released?
A
We can accelerate them using an electric field or a magnetic field.
20
Q
What is the velocity of the electron emitted by thermionic emission?
A
Voltage = Energy/Charge
Energy = VoltageCharge = eV
K.E. = eV = 1/2 * m * v^2
v = sqr rt ( (2charge*voltage) / mass)
21
Q
What is a linear accelerator?
A
A linear accelerator (LINAC) is a particle accelerator that accelerates ions to very high speeds in straight lines.
22
Q
What do LINACs use to accelerate these ions?
A
They use electric fields within and between metallic tubes which act as oppositely charged electrodes.
23
Q
What are LINACs comprised of?
A
A series of hollow cylindrical tubes of progressively increasing length each connected to an AC power supply.
24
Q
What occurs in a LINAC?
A
The ion is injected.
The ions are attracted to the midpoint of a tube.
At this point, the AC supply switches so the electrons are repelled to the exit and are attracted to the midpoint of the next tube.
This continues until the end of the accelerator.
25
What is the frequency of the AC supply switching?
Fixed, the polarity of each tube switches at a constant rate.
26
Why does the length of electrodes on an LINAC increase
the length of the electrodes increase so that the particle has the same acceleration even when it is moving faster.
Tubes switch polarity.
27
Why are linac tubes at the end the same length?
The speed of the particle has become a maximum.
28
What is a cyclotron?
A type of particle accelerator that accelerates ions from a central entry point around a spiral point.
29
What is a cyclotron used for?
Producing medical isotopes (tracers). Creating high-energy beams of radiation for radiotherapy.
30
What are cyclotrons comprised of?
Two hollow semicircular electrodes called “dees”. A uniform magnetic field is applied perpendicular to the electrodes. An AC power supply is applied across each dee, which creates an electric field in the gap between them.
31
How does a cyclotron accelerate an ion?
A source of ions is placed in the centre of the cyclotron.
They are fired into one of the dees.
The magnetic field makes them follow a circular path since it is perpendicular to their motion until they leave the dee.
The p.d. between the dees accelerates the ions across the gap to the next dee, due to the electric field in the gap.
The p.d. switches as it nears the exit, and it accelerates across the gap again to the other dee.
This cycle is repeated until they have a large enough speed and exits the cyclotron.
32
Why alternate potential difference is needed for a cyclotron?
So the particles can accelerate across the gap between the dees. Otherwise, the ions would only speed up in one direction.
33
What happens when charged particles pass through any type of medium?
They transfer energy to it.
34
What happens in the process of ionisation?
High-energy ions transfer some of their energy to the surrounding atoms. Hence removing electrons. The particles are accelerated by the electric field. Once they are discharged, they form pulses of electric current.
35
How the pulses of electric currents counted?
By electric counters connected by electrodes.
36
What are the counts counted by these electric counters?
They are interpreted as the detection of individual particles.
37
What particle detectors use ionisation as the principle on how they operate?
Geiger-Muller tubes. Spark chambers. Gas and cloud chambers.
38
What is the difference between how a LINAC and a cyclotron operates?
LINAC only uses electric fields. Cyclotrons use both electric and magnetic fields.
39
What are the two key principles which allow scientists to detect particles?
Ionisation and deflection.
40
How do you detect charged particles?
Charged particles cause ionisation, therefore, leave a trail of ions.
41
What are cloud chambers?
Supercooled vapour condenses when a particle passes through.
42
What are bubble chambers?
Hydrogen kept as a liquid (above normal boiling point). If you quickly reduce the pressure bubbles of gas form where there are trails of ions.
43
What is ionisation?
Electrons have been removed/added from a molecule.
44
What is the force that causes the deflection of charged particles?
electrostatic repulsion
45
What happens to the path of deflection if the charge is twice as much?
- deflection starts earlier
| - the final deflection is greater
46
What is the use of electric fields in particle detectors?
- used to accelerate/deflect particles
| - direction of deflection indicates charge (work is done to make particle move in same direction as the field)
47
Derive a = EQ/m
F = EQ F=ma
a = EQ/m
48
What is the use of magnetic fields in particle detectors?
- produces circular motion
- direction of curvature indicates force (flemings LHR)
- momentum found from radius of curvature
49
What is the equation for the kinetic energy transferred when a charge accelerates across a potential difference?
E = QV
50
What do electric fields do to a charged particle?
accelerate particles (speed up + change direction)
51
What do magnetic fields do to a charged particle?
accelerate particles (change the direction into a circular path)
52
How do electron guns work?
- thermionic emission release electrons
- electrons accelerated by an electric field
- passed through a small hole so the electrons are in a beam
53
What is the difference between electric field and magnetic field on a charged particle?
electric might do work but magnetic field never does work
54
What is the shape of the path that a charged particle travel in when it travels through a uniform magnetic field perpendicular to its motion?
A circular path.
55
Why does a charged particle move in a circular path?
Because the uniform magnetic field is acting perpendicular to its motion.
56
What is the force perpendicular to?
Velocity
57
What force is exerted on to the particle travelling in a magnetic field?
Centripetal force.
58
What two equations can we use to find the force on the charged particle?
F=(mv^2)/r and F=Bqv
59
What is the equation for the radius of a circular path of a charged particle?
r= mv/Bq
60
How is the radius of the circular path of a charged particle related to its momentum?
r= p/Bq
61
What 3 things does the equation r= p/Bq tell us?
Particles with larger speed/momentum move in bigger circles. Particles with greater charge move in smaller circles. Particles moving in a stronger magnetic field move in smaller circles.
62
What is the shape of the path of charged particles in electric fields?
parabolic paths (tries to get in line with electric field)
63
What can’t particle detectors that count particles (e.g. Geiger-Muller tubes) do?
They can not distinguish different types of particles.
64
What does the curvature of a particle track mean when it has a larger radius?
The particle has a larger momentum.
65
What does the curvature of a particle track mean when it has a smaller radius?
The particle has a smaller momentum.
66
What can we deduce when the radius of the particle track starts to decrease?
Its momentum is decreasing. So, velocity is decreasing. So, kinetic energy is decreasing.
67
What does it indicate when tracks appear out of nowhere?
It indicates particle and antiparticle creation.
68
Why does the kinetic energy of a charged particle decrease?
Due to ionising other particles in its path.
69
What is the shape of a particle-antiparticle creation?
A path curving in opposite directions.
70
Why is the shape of a particle-antiparticle creation curving in opposite directions?
The particle-antiparticle pair is oppositely charged. So, the magnetic force on them is oppositely directed.
71
What is the radius of the curvature of a particle-antiparticle creation the same for each path?
They have the same mass and hence, momentum.
72
What is always conserved in interactions between particles?
Energy and momentum are always conserved.
73
What do spiral paths show us?
The particle is interacting and losing energy.
74
Why don't photons leave a trail
they're neutral
75
What is the shape of neutral particle tracks?
there aren't any
76
What can particle tracks be used to work out?
- charge
- mass
- energy
77
What can we use to analyse nucleons?
High energy electron beams.
78
What is used to analyse the size and structure of nucleons?
The scattering pattern.
79
What must be comparable to what to resolve detail, like the nucleon diameter?
The de Broglie wavelength of the electron must be comparable to the size of the nucleon.
80
How can we approximate the nucleon diameter?
Using the de Broglie wavelength, λ=h/mv≈nucleon diameter
81
Do electrons experience strong nucleon force?
No.
82
What does experiencing no strong nuclear force allow electrons do?
They can get extremely close to the nucleons without interacting.
83
Why are electrons getting extremely close with the nucleons is beneficial to us?
They build up a better idea about the size of the nucleus than alpha particles.
84
What happens when electrons are accelerated to higher energies?
Their de Broglie wavelength becomes smaller.
85
What is the relationship between the de Broglie wavelength and the velocity of an electron?
Inversely proportional to each other.
86
What can we do with an extremely fast electron?
Its electron wavelength gets really small, so it can used to resolve the internal structure of the nucleon like individual quarks inside the nucleon.
87
What happens when a particle meets its antiparticle partner?
The two will annihilate.
88
What is annihilation?
When a particle meets its equivalent anti-particle, they are both are destroyed, and their mass is converted into energy in the form of gamma-ray ray photons.
89
What is the opposite of annihilation?
Pair production.
90
What is pair production?
When a photon interacts with a nucleus or atom and the energy of the photon is used to create a particle-antiparticle pair.
91
What is essential in pair production?
The presence of a nearby nucleus.
92
Why is a nucleus essential in pair production?
So that the process conserves both energy and momentum.
93
Why can’t a single photon alone produce a particle-antiparticle?
Otherwise, the conservation laws would be broken.
94
What is needed to produce an electron-positron pair?
When a photon with enough energy interacts with a nucleus.
95
Why must the energy of the photon must be above a certain value?
So, it can provide the total rest mass energy of the particle-antiparticle pair.
96
What is the equation for the energy of a photon needed to provide the total rest mass energy of the particle-antiparticle pair?
ΔE=Δm c^2, where ΔE is the rest mass energy of the particle (J), Δm is the rest mass of the particle (kg), and c is the speed of light.
97
What does E=mc^2 demonstrate?
Energy can turn into mass and mass can turn into energy. When energy is converted to mass you make equal amounts of matter and antimatter.
98
when energy is converted to mass you make equal amounts of matter and antimatter?
The energy carried by a single photon must be at least twice the rest-mass energy required. So, 2*ΔE=2*Δm c^2
99
What is the equation for the energy carried away by each of the two photons after annihilation?
E_photon=hf=hc/λ= Δm c^2
100
When is E=hf relevant?
Only relevant for photons.
101
What is 1 eV equivalent in joules?
1.6×10^(-19) J
102
What does one electron Volt represent?
The amount of energy transferred to an electron accelerated across a potential difference of 1V.
103
How to convert from eV to joules?
Multiply eV value by 1.6×10^(-19) to get to joules.
104
How to convert from joules to eV?
Divide J value by 1.6×10^(-19) to get to eV.
105
How to convert from MeV to joules?
n MeV = n×10^6 eV (multiply by 1.6×10^(-19)) = 1.6n×10^(-13) J.
106
How to convert from joules to MeV?
n J (divide by 1.6×10^(-19))(divide by 1×10^6) = n/1.6×10^13 MeV.
107
How to convert from GeV to joules?
n GeV = n×10^9 eV (multiply by 1.6×10^(-19)) = 1.6n×10^(-10) J.
108
How to convert from joules to GeV?
n J (divide by 1.6×10^(-19))(divide by 1×10^9) = n/1.6×10^10 GeV.
109
What are the 3 units of mass?
Kg, u,MeV/c^2 or GeV/c^2
110
What is the mass unit “u”?
The unified atomic mass unit, 1u is one-twelfth the mass of a single carbon-12 atom.
111
What is the mass unit “MeV/c^2 or GeV/c^2 ”?
Derived from ΔE=Δm c^2.
112
How to convert from kg to u?
Multiply kg value by 6.022×10^26 (Avogadro’s constant * 1000) to get u value.
113
How to convert from g to u?
Multiply g value by Avogadro’s constant (6.022×10^23) to get u value.
114
How to convert from u to kg?
Divide u value by 6.022×10^26 (Avogadro’s constant * 1000) to get kg value.
115
How to convert from kg to MeV/c^2 or GeV/c^2 ?
Substitute kg into ΔE=Δm c^2.
Convert J to eV by dividing it by 1.6×10^(-19).
Convert the standard form from eV to MeV or GeV.
And divide by c^2.
116
How to convert fromMeV/c^2 or GeV/c^2 to kg?
Multiply MeV/c^2 or GeV/c^2 value by c^2.
Convert MeV or GeV to eV.
Convert eV to J by multiplying by 1.6×10^(-19).
Divide by c^2 to get mass in kg.
117
How to convert from u to MeV/c^2 or GeV/c^2 and back? Convert to kg first then continue from there.
Convert to kg first then continue from there.
118
Why is GeV/c a unit of momentum?
p=mv, GeV/c^2 is a unit of mass
119
What speeds do accelerated particles reach?
Speeds that are very close to the speed of light.
120
What could happen when accelerated particles reach high velocities and energies?
Relativistic effects occur.
121
What are the 2 relativistic effects?
Time dilation and length contraction.
122
What is time dilation?
When clocks run slower for these moving particles.
123
Why is time dilation beneficial to unstable particles?
Unstable particles that have short lifetimes can survive for much longer in laboratory if they are moving very quickly.
124
Why does unstable particles lasting longer due to time dilation is useful to us?
They will leave longer tracks in particle detectors. Thus, making detection easier.
125
Give a real-life example of time dilation affecting particles.
Muon created high up in the atmosphere has a lifetime of about 2μs. But a lot is detected at sea-level and the time to get to sea level is longer than 2μs. Since these muons are travelling at relativistic speeds, their lifetime is dilated to times higher than 2μs due to time dilation.
126
What is length contraction?
When travelling at relativistic speeds, we travel more than expected.
127
Why is length contraction beneficial to unstable particles?
Unstable particles with very short lifetimes would not travel appreciable distances without relativistic effects like length contraction.
128
When is a particle considered travelling at speeds close to a speed of light?
90% the speed of light.
