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Physics The Good One > 08 nuclear and particle physics > Flashcards

08 nuclear and particle physics Flashcards

1
Q

Nucleon number

A

Number of neutrons and protons in the atom.

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2
Q

Proton number

A

Number of protons in the nucleus.

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3
Q

Rutherford’s scattering experiment

A

A stream of alpha particles from a radioactive source were fired at a very thin gold foil sheet. The number of alpha particles at different angles was recorded.

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4
Q

Rutherford’s scattering experiment conclusions

A

Most (fast charged) alpha particles went straight through, therefore an atom is mostly empty space.
Some alpha particles deflected at an angle greater than 90, therefore part of the atom must be more massive than the alpha particle—this is the nucleus.
Alpha particles were repelled, so the nucleus must be positively charged.
Since atoms are neutral overall, electrons must be in the outside of the atom.

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5
Q

Nuclear model

A

Concentrated mass in the center, strong positive charge in the center, negative charge spread across the remaining atom.

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6
Q

Thermionic emission

A

The process by which free electrons are emitted from the surface of a metal when external heat energy is applied.

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7
Q

How do electron guns work

A

Thermionic emission releases electrons, electrons are accelerated by an electric field, passed through a small hole so the electrons are in a beam.

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8
Q

Energy gained by electron (eV)

A

Accelerating voltage.

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9
Q

How does a cyclotron work

A

Two semi-circular electrodes with alternating charge have a gap between them. The electric field between the electrodes accelerates the charged particle across. A perpendicular magnetic field is applied to keep the particle moving in a circular path.

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10
Q

Why does the radius of a charged particle in a cyclotron increase

A

Because velocity is proportional to radius, so as it is accelerated, the radius increases.

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11
Q

How does a LINAC work

A

A high-frequency AC current is applied to the electrodes so that their charge changes from + to -. The charged particle is always repelled from the previous electrode and attracted to the next one, hence causing it to be accelerated through the electric field to the next electrode.

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12
Q

Why does the length of electrodes on a LINAC increase

A

The length of the electrodes increases so that the particle has the same acceleration even when it is moving faster. Tubes switch polarity.

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13
Q

Hadrons

A

Particles that feel the strong interaction.

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14
Q

Baryons

A

Hadrons made of 3 quarks.

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15
Q

Mesons

A

Hadrons made of two quarks: a quark and an anti-quark.

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16
Q

Proton

A

Baryon: uud.

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17
Q

Neutron

A

Baryon: udd.

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18
Q

K+

A

Meson: u ŝ.

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19
Q

K

A

Meson: d ŝ.

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20
Q

K-

A

Meson: s û.

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21
Q

π+

A

Meson: u antidown.

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22
Q

π

A

Meson: u û OR d antidown.

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23
Q

π-

A

Meson: d û.

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24
Q

Anti Mesons

A

K and π are their own anti-particles, whereas K+ is the antiparticle of K-.

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25
Leptons
Fundamental particles that don’t feel the strong interaction. They interact with other particles via the weak interaction, gravity, and the electromagnetic force.
26
Electrons
Stable leptons.
27
Muons
Heavy unstable leptons (eventually decay to an electron).
28
Tau
Heaviest, least stable lepton.
29
Neutrino
Electrons, Muons, and Taus have their own neutrino, which has zero mass and zero charge.
30
Neutron decay
Unstable, so decays to a proton via beta decay.
31
Antiparticles
Each particle has a corresponding antiparticle with identical mass and opposite charge, baryon and lepton numbers.
32
E=mc^2
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.
33
Pair production
If a particle is produced, an anti-particle must also be produced.
34
Relativity
The mass of an object increases as velocity increases due to relativistic effects.
35
Converting from kg to MeV/c^2
Convert mass to energy (e=mc^2), then convert to MeV.
36
Converting from MeV/c^2 to kg
Convert to J/C^2, then divide by C^2.
37
eV -> joules
e.
38
Joules -> eV
/ e.
39
Production of an anti-particle pair
Only happens if a gamma photon has enough energy to create mass. Happens near a nucleus to conserve momentum.
40
Annihilation
Occurs when a particle meets an anti-particle. All mass is converted into energy.
41
Conservation Laws in Particle Reactions
Charge, Baryon Number, Lepton Number, Mass/Energy, Momentum.
42
Detecting charged particles
Charged particles cause ionization, therefore leave a trail of ions.
43
Cloud chambers
Supercooled vapor condenses when a particle passes through.
44
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.
45
Charged particles in magnetic field
Circular paths.
46
Charged particles in electric fields
Parabolic paths.
47
Spiral paths
The particle is interacting and losing energy.
48
Neutral particle tracks
There aren’t any.
49
Why are collisions high energy
Energy required to overcome electrostatic repulsion. Since particles move fast, the energy/momentum must be high, resulting in a shorter de Broglie wavelength.
50
Why are LINAC tubes at the end the same length?
The speed of the particle has become a maximum.
51
Ionization
Electrons have been removed/added from a molecule.
52
Charged particle in magnetic field
Circular.
53
Charged particle in electric field
Parabolic (tries to get in line with the electric field).
54
Why don’t photons leave a trail
They’re neutral.
55
When two particles are formed from a photon, why do their tracks curve away from each other?
They are in a magnetic field, implying one is positively charged and one is negatively charged, charge is conserved.
56
What does the curvature of the spirals for a charged particle in a magnetic field tell you?
The momentum of the particle (more momentum means a bigger radius).
57
Difference between electric field and magnetic field on a charged particle
Electric might do work, but a magnetic field never does work.
58
When alpha particles are fired at a gold foil, what happens to most of them/what does this mean?
They pass straight through—most of the atom is empty space.
59
Why are some alpha particles scattered through 180 when fired at gold foil?
Most of the mass is in the center, which is charged positively, hence deflecting the positive charge of the alpha particle.
60
What is the force that causes deflection of charged particles?
Electrostatic repulsion.
61
What happens to the path of deflection if the charge is twice as much?
Deflection starts earlier, the final deflection is greater.
62
Use of electric fields in particle detectors
Used to accelerate/deflect particles. The direction of deflection indicates charge (work is done to make the particle move in the same direction as the field).
63
Derive a = EQ/m
F = EQ, F = ma, a = EQ/m.
64
Use of magnetic fields in particle detectors
Produces circular motion. The direction of curvature indicates force (Fleming’s LHR). Momentum is found from radius of curvature.
65
Kinetic energy transferred when a charge accelerates across a potential difference
E = QV.
66
Why are only a low proportion of decays detected?
Emissions in all directions. Some emitted particles may be absorbed by the material in the sample, some absorbed by the window, some pass through the detector.
67
Creation
Creates a particle and an antiparticle. E = mc^2.
68
Annihilation
A particle and its antiparticle are destroyed simultaneously in a conversion to energy (2 photons).
69
Electronvolt
Energy required to accelerate an electron through a pd of 1V.
70
Antimatter
Same mass, opposite charge (+other properties).
71
Electric fields…
Accelerate particles (speed up + change direction).
72
Magnetic fields…
Accelerate particles (change the direction into a circular path).
73
What can particle tracks be used to work out?
Charge, mass, energy.
74
LINAC
A series of electrode tubes of increasing length with an AC pd applied across them.
75
What does firing electrons at a hydrogen target tell us
Proton is not uniform, it has some empty space since some electrons passed through, made up of smaller particles called quarks.
76
Fundamental particle
Has no internal structure / not made up of other particles.
77
Atomic process that produces emission spectra
Electron drops down energy levels and de-excites, releasing energy.
78
Why were scientists able to predict the 6th quark?
Standard model symmetry, quarks came in pairs, 6 known leptons but only 5 known quarks.
79
Why is GeV/c a unit of momentum
GeV/c^2 is a unit of mass, p = mv.
80
Why did it take a long time to find experimental evidence for the top quark?
Large mass, needs a lot of energy.
81
Quark order
Up, Down, Charm, Strange, Top, Bottom.
82
Last quark to be discovered
Top.
83
Lightest quark
Up.
84
Heaviest quark
Top.
85
Lambda particle
Baryon: u d s.

Physics The Good One (16 decks)

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