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Physics > Particle Physics > Flashcards

Particle Physics Flashcards

1
Q

The 3 conservation laws observed in nuclear reactions

A

Conservation of mass - energy
Conservation of momentum
Conservation of charge

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2
Q

Law of conservation of mass - energy

A

E = mc^2
if mass is lost in a nuclear reaction it will be converted to energy and energy may be converted to mass.
the total mass - energy total will remain the same

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3
Q

Law of conservation of momentum

A

in any interaction between two particles in a closed system the total momentum before the interaction ewuals the total momentum after the interaction

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4
Q

Law of conservation of charge

A

In a nuclear reaction the total amount of electric charge before the reaction equals the total amount of electric charge after the reaction

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5
Q

normal unit of energy

A

joule

J

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6
Q

teeny tiny unit of energy

A

eV

electron volt

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7
Q

1 eV =

A

1.6 x 10^-19 joules

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8
Q

1 keV =

A

1 x 10^3

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9
Q

1 MeV =

A

1 x 10^6

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10
Q

1 GeV =

A

1 x 10^9

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11
Q

what page in the maths tables can you find milli, kilo, giga etc.

A

pg 45

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12
Q

normal unit of mass

A

kg

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13
Q

teeny tiny unit of mass

A

u

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14
Q

u

A

unified atomic mass unit

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15
Q

where can you find the charge on the electron (same as eV to joule)

A

pg 46

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16
Q

where can you find the conversion of u to kg

A

pg 47 of the maths tables

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17
Q

how to find the energy of a mass converted to energy

A

E = mc squared

put everything in joules and then kg and then convert back if asked for it

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18
Q

how to calculate the energy released in a nuclear equation

A

mass of first nucleus - (mass of second nucleus + mass of emitted particle) = m
e = mc squared

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19
Q

where does most of the kinetic energy released in a nuclear equation go?

A

as kinetic energy

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20
Q

how do you get the ratio of kinetic energies

A

kinetic energy 1 / kinetic energy 2

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21
Q

what should get nearly all of the energy

A

the smallest particle

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22
Q

if the momentum of the electron (beta particle) differs before and after, what is needed

A

a new particle, the neutrino

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23
Q

who proved that E=mc squared

A

walton and Cockcroft

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24
Q

walton and Cockcroft experiment

A

they bombarded lithium with protons

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25
Q

walton and Cockcroft experiment: first thing they did

A

protons were produced in a hydrogen discharge tube and were fed into an accelerator tube

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26
Q

walton and Cockcroft experiment: what accelerated the protons?

A

a voltage of the order 700,000

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27
Q

walton and Cockcroft experiment: how did the protons hit the lithium target?

A

at an angle of 45º

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28
Q

walton and Cockcroft experiment: how were the particles emitted?

A

in opposite directions at right angles to the protons

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29
Q

walton and Cockcroft experiment: what did the emitted particles cause?

A

scintillations at a fluorescent screen

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30
Q

walton and Cockcroft experiment: how were the scintillations observed?

A

with the help of a microscope

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31
Q

walton and Cockcroft experiment: what were the emitted particles?

A

nuclei of helium (alpha particles)

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32
Q

walton and Cockcroft experiment: equation

A

L7 + H -> He + He + energy

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33
Q

walton and Cockcroft experiment: what was noted about the energies

A

the energy of the emitted alpha particles was far greater than the energy of the incoming protons

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34
Q

walton and Cockcroft experiment: what did the inconsistency in energies show?

A

that energy had been obtained from mass

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35
Q

transmutation

A

changing one element into another

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36
Q

who performed the first transmutation and equation

A

rutherford

He + N14 -> O27 + H

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37
Q

walton and Cockcroft experiment: what achievement did they carry out?

A

the first transmutation using artificially accelerated particles

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38
Q

what does a linear accelerator do?

A

it successively accelerates electrons as they pass through a set of cylindrical electrodes

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39
Q

linear accelerator: what is applied to the electrodes

A

an alternating current is applied to each electrode so that it is positive as electrons approach and negative as electrons leave it

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40
Q

linear accelerator: where are the electrons accelerated?

A

at the gaps

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41
Q

when does the length of an accelerator not need to be so long?

A

when particles are allowed to follow a circular path

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42
Q

cyclotron: how do the particles move?

A

a magnetic field is applied perpendicularly to the 2 semi circular shaped cavities in which the charged particles will move

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43
Q

cyclotron: what happens when the charged particle from the source enters the magnetic field?

A

it follows a circular path

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44
Q

cyclotron: how do you ensure that the particle accelerates each time it crosses the gap?

A

an alternating voltage is applied across the 2 semi circles

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45
Q

cyclotron: what happens as the charged particle gains speed

A

the radius of its circular motion increases and it spirals outwards from the source

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46
Q

cyclotron: equation for radius

A

r = mv/Bq

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47
Q

what happens when the charged particle gets to the edge of the cyclotron

A

it leaves and gets fired at its target

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48
Q

2 advantages of circular accelerators

A
  • they are more compact than linear accelerators

- they accelerate particles at higher speeds than linear particles do

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49
Q

if the reaction takes place in a cloud chamber?

A

a magnetic field will cause the 2 particles (1 is charged negatively and one is charged positively) to be deflected in opposite directions

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50
Q

what happens when high energy Ɣ rays are fired at a sheet of lead

A

an electron and a positron are produced

51
Q

explain this: when high energy Ɣ rays are fired at a sheet of lead an electron and a positron are produced

A

the energy of the photon is converted into the mass of the two particles, any energy of the photon that is not changed to mass becomes the kinetic energy of the 2 new particles

52
Q

pair production equation

A

hf = m1 c squared + m2 c squared + E1 + E2

53
Q

2 things that are conserved in the reaction of pair production

A

charge and momentum

54
Q

explain how charge is conserved in the reaction of pair production

A

the incoming photon has no charge and since the electron and positron have equal and opposite charge there is no net charge after the reaction

55
Q

each particle has

A

an antiparticle; eg. an antiproton

56
Q

symbol for antiparticle

A

a bar over the particle

57
Q

if a particle has a charge

A

its antiparticle has an opposite charge

58
Q

why are antiparticles difficult to detect

A

because when a particle meets its antiparticle both are annihilated and the mass of the particles turns to energy

59
Q

where are positrons and antiprotons kept at CERN

A

in circular evacuated containers and are kept in place using magnetic fields

60
Q

what is pair annihilation the reverse of?

A

pair production

61
Q

an example of pair annihilation

A

e+ + e- -> y + y

62
Q

2 things that are conserved in pair annihilation

A

momentum and charge

63
Q

how do we know that momentum is conserved in pair annihilation?

A

its the reason why 2 photons are produced and travel in opposite directions

64
Q

what are pair production and pair annihilation examples of?

A

the equivalence of mass and energy as predicted by Einstein

65
Q

where can pair annihilation be used?

A

in the study of brain abnormalities

66
Q

diagnostic technique of studying brain abnormalities

A

positron emission tomography (PET)

67
Q

explain PET

A

Radioactive materials that decay by positron emission are used, the positrons annihilate the electrons from damaged body tissue and the emitted photons are picked up by detectors and give an outline of the damaged tissue

68
Q

gravitational force

A

an attractive force that is hardly noticeable unless the masses in question are quite large e.g. planets

69
Q

Newton’s law of gravitational force

A

the magnitude of the force is inversely proportional to the square of the distances between the centres of the 2 masses

70
Q

equation for Newton’s law of gravitational force

A

F = Gm1m2 / d squared

71
Q

over what distance does gravitational force act?

A

over infinite distance

72
Q

effect of gravitational force in particles around the nucleus

A

negligible

73
Q

what is currently believed that transmits gravitational force

A

a particle; the graviton

74
Q

Part of the electrostatic force between 2 charges is given by what?

A

coulumb’s law

75
Q

Coulumb’s Law

A

F = q1q2/4pied squared

76
Q

is the electrostatic force attractive or repulsive

A

can be either depending on the sign of the charges

77
Q

the second part of the electromagnetic force is?

A

the magnetic force between moving charges

78
Q

function of the magnetic force between moving charges in our lives

A

it is the force that binds electrons and protons together and that binds atoms together to form matter

79
Q

does the the magnetic force between moving charges obey the inverse square law?

A

yes

80
Q

when does the magnetic force between moving charges decline

A

with distance

81
Q

range of the magnetic force between moving charges

A

infinite

82
Q

what is believed about how the electromagnetic force is transmitted

A

by the exchange of photons

83
Q

the strongest of the 4 forces

A

the strong nuclear force

84
Q

function of the strong nuclear force

A

holds the protons and neutrons together in the nucleus

85
Q

what would happen in the nucleus if the strong force wasn’t there

A

the positive protons would repel

86
Q

range of the strong force

A

10 ^ -15 m

87
Q

does the electron experience the strong force?

A

no

88
Q

what must the strong force also be?

A

must be sufficiently repulsive to prevent the nucleus from collapsing in on itself

89
Q

for the strong force, what are the messenger particles called?

A

gluons

90
Q

what do gluons do?

A

they transmit the strong force between elementary particles

91
Q

who experiences the weak nuclear force?

A

all particles

92
Q

range of the weak nuclear force

A

10 ^-18 m

93
Q

how does the neutrino interact with matter?

A

via the weak force

94
Q

example of neutrino interacting with matter via the weak force and equation

A

an antineutrino and a proton interact to produce a positron and a neutron
-v- + p -> n + e+

95
Q

what shows that weak interactions have a low probability of happening

A

a neutrino can pass through the earth without interacting

96
Q

what is the weak force responsible for?

A

the conversion of neutrons to protons in the process of beta decay in radioactivity

97
Q

what is proposed about the weak force?

A

that it is transmitted by photons and massive W-particles and X-particles?

98
Q

forces in order of descending relative strength

A

strong nuclear
electromagnetic
weak nuclear
gravitational

99
Q

strong nuclear affects

A

proton, neutron, quark

100
Q

weak nuclear affects

A

all particles

101
Q

electromagnetic affects

A

charged particles

102
Q

gravitational affects

A

all particles

103
Q

criterion for the order on which they put the particles from the particle zoo

A

whether or not they feel the nuclear force

104
Q

leptons

A

affected by the weak force nut not the strong force

105
Q

hadrons

A

hadrons are affected by both the strong force and the weak force

106
Q

6 leptons

A 
electron
neutrino
muon 
tau
muon neutrino
tau neutrino
107
Q

2 groups of hadrons

A

baryons

mesons

108
Q

what forces can leptons and hodrons be affected by as well as strong force

A

gravitational force, and if charged the electromagnetic force

109
Q

what does evidence suggest at the moment about leptons

A

that they are elementary particles

110
Q

elementary particles

A

cannot be subdivided into small particles

111
Q

baryons’ mass

A

similar to or greater than that of the proton

112
Q

mesons’ mass

A

less than than of the baryon but greater than that of leptons

113
Q

are baryons and mesons fundamental particles

A

no

114
Q

what are baryons and mesons composed of

A

quarks

115
Q

quarks

A

the elementary particles that make up baryons and mesons

116
Q

first 3 quarks discovered

A

up (u) down (d) and strange (s)

117
Q

other 3 quarks

A

charm (c), top(t) and botto (b)

118
Q

quarks’ charges

A

1/3 or 2/3

119
Q

how many antiquarks are there?

A

6

120
Q

why is it very difficult to isolate a quark

A

they feel all 4 forces but principally the strong nuclear force

121
Q

what is a meson made up of?

A

any one quark and any one antiquark

122
Q

what are baryons made up of?

A

any 3 quarks and antibaryons are made up of any 3 antiquarks

123
Q

what are now believed to be the fundamental constituents of matter?

A

the 6 quarks and the 6 leptons

Physics (11 decks)

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