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OCR A-Level Physics > 6.4 Nuclear & Particle Physics > Flashcards

6.4 Nuclear & Particle Physics Flashcards

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1
Q

what was the alpha particle scattering experiment?

A

Ernest Rutherford fired a beam of fast moving alpha particles at a thing gold foil to see how the alpha particles were deflected, the detector was a zinc sulphide screen that would produce a faint flash of light whenever an alpha particle hit it

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2
Q

what were the deductions from the alpha particle scattering experiment?

A
  • the vast majority of the mass of the atom is contained within a small volume called the nucleus
  • the nucleus has a positive charge
  • the nuclear distance is considerably smaller than the diameter of the atom, meaning that the atom is mostly empty space
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3
Q

what was the evidence in the experiment that showed there was a very dense nucleus?

A

most of the mass must be in the nucleus since he fast alpha particles (with high momentum) are deflected by the nucleus

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4
Q

what was the evidence in the experiment that showed the nucleus was positive?

A

some of the alpha particles were deflected through large angles, so the centre of the atom must have a large, positive charge to repel them, Rutherford named this the nucleus

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5
Q

what was the evidence in the experiment that showed that the atom is mostly made up of empty space?

A

most of the fast, charged alpha particles went straight through the foil, so the atom is mainly empty space

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6
Q

what is the charge and mass of a proton (in terms of e for charge and u for mass)?

A

+1 charge

mass = 1

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7
Q

what is the charge and mass of a neutron (in terms of e for charge and u for mass)?

A

0 charge

mass = 1

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8
Q

what is the charge and mass of a electron (in terms of e for charge and u for mass)?

A

-1 charge

mass = 1 / 1840 (negligible)

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9
Q

what is the defintion of nucleon number?

A

no. of protons and neutrons inside the nucleus (also known as the mass number)

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10
Q

what are isotopes?

A

isotopes contain the same no. of protons and electrons but different no. of neutrons

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11
Q

what is mass number equal to?

A

no. of protons and neutrons

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12
Q

what is atomic number equal to?

A

just no. of protons

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13
Q

what is the strong nuclear force?

A

the strong nuclear force acts between nucleons and holds the nucleus together against the electrostatic attraction repulsion of the protons

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14
Q

is the strong nuclear force attractive or repulsive?

A

(trick question) it is BOTH, it is attractive to about 3 x 10^-15 and 0.5 x 10^-15m, it is a repulsive force between nucleons for distances of separation up to around 0.5x10^-15m, it is a SHORT RANGE force - it doesn’t act over large distances

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15
Q

how much bigger is the diameter of the whole atom compared to the diameter of the nucleus?

A

roughly 10,000 times greater

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16
Q

what is the relationship between the radius of a nucleus and the nucleon number?

A

R (radius) is proportional to the cube root of the nucleon number A, comes from the equation R = RoA^1/3

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17
Q

what will a graph of radius of nucleus against nucleon number look like (think about the relationship)?

A

exponential, starts steep then decreasing gradient until it plateaus

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18
Q

what will a graph of radius of nucleus against cube root of nucleon number look like (think about the relationship)?

A

constant gradient, straight line upwards

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19
Q

what is the equation that links radius of a nucleus to nucleon number?

A

R = Ro x A^1/3
where Ro = a constant (1.4 x 10^-15)
R = nuclear radius
A = nucleon number

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20
Q

what is greater atomic density or nuclear density?

A

nuclear density is much greater than atomic density

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21
Q

what are the two equations needed to calculate nuclear density? to get to ρ = 3Mn / (4πro^3)?

A

ρ = m / v
and assuming v = 4/3πr^3, subbing in R^3 = Ro^3A from R = Ro x A^1/3 gets you to a simplified formula to work out the mean density of the nucleus: ρ = 3Mn / (4πro^3)

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22
Q

what are fundamental particles?

A

fundamental particles are particles that cannot be broken down into smaller components (e.g electrons, quarks)

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23
Q

what are hadrons?

A

hadrons are particles consisting of a combination of quarks to give a net zero or whole number change, neutrons and protons are hadrons - hadrons are particles that feel the strong force and weak force e.g protons and neutrons

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24
Q

what are leptons?

A

lepton are fundamental particles, electrons and neutrinos are leptons - leptons are particles that feel the weak force and not the strong force, e.g electrons and neutrinos

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25
Q

what are quarks?

A

quarks are components of hadrons and have a fractional electric charge, to date, they are believed to be fundamental particles, there are different types of quark, for example, up, down and strange quarks

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26
Q

what are neutrinos?

A

a neutrino is a fundamental particle (lepton) with almost no mass and zero charge, each neutrino has an antimatter partner called an antineutrino

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27
Q

what is the weak nuclear force?

A

the weak nuclear force is felt by both quarks and leptons, it can change quarks from one type to another or leptons from one type to another or leptons from one type to another and is responsible for beta decay

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28
Q

what is an antiparticle?

A

an antiparticle is a particle of antimatter that has the same rest mass (mass at zero speed) but, if charged, the equal and opposite charge to its corresponding particle, for example the positron (e+) is the antiparticle of the electron (e-) - every known particle has its own ‘opposite particle’ of antimatter particle called an antiparticle

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29
Q

what are the two classifications of particles?

A

hadrons and leptons

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30
Q

are hadrons fundamental?

A

no - they can be broken down into quarks

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31
Q

what quarks are in a proton?

A

uud - two up and one down making the charge +1, 2/3 +2/3 - 1/3 = 1

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32
Q

what quarks are in a neutron?

A

udd, one up and two down making the charge 0, 2/3 - 1/3 - 1/3 = 0

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33
Q

what charge does an up quark have?

A

+2/3

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34
Q

what charge does a down quark have?

A

-1/3

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35
Q

what does each lepton also have?

A

a neutrino which is also fundamental particle, and which is produced in beta decay

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36
Q

what is special about neutrinos?

A

they have ZERO MASS and ZERO CHARGE

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37
Q

what is the Baryon number of quarks?

A

1/3

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38
Q

what does the squiggly line above a particle denote?

A

an antiparticle

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39
Q

what is the charge and name of a proton’s antiparticle?

A

antiproton, charge = -1

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40
Q

what is the charge and name of a neutron’s antiparticle?

A

antineutron, charge = 0

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41
Q

what is the charge and name of an electron’s antiparticle?

A

positron, charge = +1

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42
Q

what is the charge and name of a neutrino’s antiparticle?

A

antineutrino, charge = 0

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43
Q

what is radioactive decay?

A

radioactive decay is the spontaneous and random decay of an unstable nucleus into a more stable nucleus by the emission of an α, β or γ radiation

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44
Q

what is the nature, mass, charge and symbol of an alpha particle?

A
  • helium atom, made up of 2 protons and 2 neutrons
  • mass = 4u
  • charge = +2e
  • symbol = α
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45
Q

what is the nature, mass, charge and symbol of a beta-minus particle?

A
  • electron
  • mass = 1/1840 (negligible)
  • charge = -e
  • symbol = β-
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46
Q

what is the nature, mass, charge and symbol of a beta-plus particle?

A
  • positron
  • mass = 1/1840 (negligible)
  • charge = +e
  • symbol = β+
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47
Q

what is the nature, mass, charge and symbol of a gamma ray?

A
  • high freq. electromagnetic radiation
  • mass = zero
  • charge = zero
  • symbol = γ
48
Q

what happens in beta minus decay in terms of numbers of protons and neutrons?

A

a neutron is converted to a proton which produces an electron and an electron anti-neutrino

49
Q

what happens in beta plus decay in terms of numbers of protons and neutrons?

A

a proton is converted to a neutron which produces a positron and an electron neutrino

50
Q

which radiation is the most penetrating out of alpha, beta and gamma?

A

gamma, beta then alpha

51
Q

which radiation is the most ionising out of alpha, beta and gamma?

A

alpha, beta then gamma

52
Q

what is beta minus decay?

A

in beta minus decay a neutron in the nucleus breaks down into a proton under the influence of the weak nuclear force, and a beta minus particle (an electron) and an electron anti-neutrino are emitted

53
Q

what is beta plus decay?

A

in beta plus decay a proton in the nucleus breaks down into a neutron under the influence of the weak nuclear force, and a beta plus particle (a positron) and an electron neutrino are emitted

54
Q

what is the quark change when a nuclei undergoes beta minus decay?

A

udd changes into uud

neutron into proton

55
Q

what is the quark change when a nuclei undergoes beta plus decay?

A

uud changes into udd

proton into neutron

56
Q

what is the equation in terms of the quark model for beta minus decay?

A

d —> u + e + ̅ν

57
Q

what is the equation in terms of the quark model for beta plus decay?

A

u —> d + e + v

58
Q

what are the names of the nuclei after it has undergone alpha decay?

A

daughter nuclei from parent nuclei

59
Q

can you get pure gamma decay?

A

no - gamma radiation frequently accompanies either α or β decay, but never occurs as purely a gamma decay

60
Q

what happens to the rate of activity of a radioactive sample over time (the rate at which unstable nuclei decay)?

A

the rate decreases over time because there are fewer unstable nuclei

61
Q

what is the equation that links activity to no. of undecayed nuclei?

A

A = λN
where A = activity
λ = decay constant
N = no. of undecayed nuclei

62
Q

what is activity in terms of a radioactive source?

A

activity, A, is the number of nuclear decays (the number of gamma rays emitted) per unit time, an activity of one decay per second is called one becquerel Bq

63
Q

what is the decay constant?

A

λ, the decay constant is the probability that an individual nucleus will decay per unit time, given by λ = A / N and has units (s^-1)

64
Q

what is the definition for half life?

A

the half-life (t1/2) is defined as the mean time taken for the activity of a source, or the no. of undecayed nuclei present, to halve

65
Q

what is the equation for the half life of an isotope?

A

t1/2 = ln(2) / λ

66
Q

what are the two exponential equations, one for activity and no. of undecayed nuclei?

A

A = Ao x e^-λt
N = No x e^-λt
where A = activity, Ao = initial activity
N = no. of undecayed nuclei, No = initial no. of undecayed nuclei, λ = decay constant, t = time spent decaying

67
Q

outline an experiment to investigate the absorption of α-particles, β and γ radiation

A
  • you can investigate the penetrating power of alpha, beta and gamma radiation using a Geiger-Muller tube and counter to detect the radiation passing through sheets of different materials placed between the tube and the radioactive source
  • the background radiation count rate (the number of ionising events detected per second or per minute when no radioactive source is nearby) must be first measured and then subtracted from all recorded count rates. Use paper and aluminium foils and pieces of lead of different thickness to investigate what thickness of each material stops each type of radiation
68
Q

how does carbon dating work?

A

the ratio of carbon 14 to non-radioactive carbon 12 in dead organic matter decreases with time, so the ratio of activity of no. of carbon-14 nuclei in a dead organic sample compared to a living sample can be used for dating

69
Q

what are the two limitations of carbon dating?

A
  • Because the quantity of carbon-14 is very small count rates are correspondingly small and after a few half lives may be indistinguishable from the background count rate
  • the ratio of carbon-14 to carbon-12 in the air and in all living things is assumed to be constant, that is there has been no variation over time, this may not be true if there has been changes in the rate at which carbon-14 is produced in the atmosphere
70
Q

what is Einstein’s mass energy equation?

A

E = mc^2

71
Q

what is annihilation?

A

annihilation is the process in which a particle and its antiparticle interact and their combined mass is converted to energy via E = mc^2 (photons are released)

72
Q

what is pair production?

A

pair production is the process of creating a particle-antiparticle pair from a high-energy photon (like from annihilation)

73
Q

what has greater mass, the total mass of the separated nucleons or the total mass of the nucleons?

A

total mass of the separated nucleons has MORE ENERGY than the total mass of the nucleons

74
Q

why is there a difference between the mass of the separate nucleons and the mass of the whole nucleus?

A

this arises from the fact that all the nucleons are bound together by the strong nuclear force, this means work has to be done to separate the nucleons, so the separated nucleons gain potential energy and by Einstein’s mass-energy equation they then have more mass

75
Q

in radioactive decay, how is energy released? in what form?

A

energy is released in the form of the kinetic energy of the fast moving alpha or beta particles, and may also be released as gamma ray photons

76
Q

what is the origin of the energy released in radioactive decay?

A

the origin of this energy is the conversion of some of the masses of the particles involved into energy

77
Q

what is the opposite of pair production?

A

annihilation (and vice versa)

78
Q

what can the instability of a nucleus be caused by?

A
  • too many neutrons
  • too few neutrons
  • too much energy in the nucleus
  • too many nucleons in total (too heavy)
79
Q

can you ever get a free quark on its own?

A

no - you cannot get a free quark on its own, you cannot separate quarks, if you tried to the energy put in would just get converted into more quarks and antiquarks, you just get pair production

80
Q

when energy is converted to mass what is the ratio between matter and antimatter produced?

A

equal amounts of matter and antimatter

81
Q

outline an experiment to determine the half-life of an isotope such a protactinium

A

(see page 215 for diagram or page 74 in revision guide)

  • use a protactinium generator, a bottle containing a uranium salt, the decay products of uranium (including protactinium-234) and two solvents, which separate out into layers
  • shake the bottle to mix the solvent together
  • wait for the liquids to separate, the protactinium-234 will be in solution in the top layer, and the uranium salt will stay in the bottom layer, then you can put the Geiger-Muller tube at the top layer to measure the activity of the protactinium-234
  • as soon as the liquids separate, record the count rate (how many counts in 10 secs), re-measure the count rate at sensible intervals (e.g every 30 seconds)
  • once you’ve collected your data, leave the bottle to stand for at least ten mins, then take the count rate again, this is the background count rate corresponding to background radiation (you could also do this at the beginning of the experiment, before shaking the bottle)
  • subtract this value from your measured count rates, then plot a graph of count rate against time, it should look like an exponential downwards on decreasing gradient, you can use your graph to work out the half-life by looking at how long it takes for the count rate (or activity) to halve
82
Q

what does alpha decay occur in?

A

very heavy nuclei like uranium and radium, the nuclei of these atoms are too massive to be stable

83
Q

what doe beta minus decay occur in?

A

neutron-rich nuclei, where they have many more neutrons than protons in their nucleus

84
Q

how can you calculate the binding energy per nucleon?

A

binding energy / nucleon number

85
Q

what is the mass defect?

A

the difference in mass between the mass of a nucleus and the total mass of its separate nucleons (extra mass)

86
Q

what is the mass defect in a decay reaction equal to?

A

this extra mass (mass defect) is equivalent to the binding energy of a nucleus and is released as energy

87
Q

what is the definition of binding energy?

A

binding energy of a nucleus is the minimum energy required to separate the nucleus (protons and neutrons) into its constituent parts

88
Q

what does the graph of binding energy per nucleon against nucleon number look like? what does it mean?

A

you get a curve, a high binding energy per nucleon means more energy is needed to remove nucleus from the nucleus so in other words the most stable nuclei occur around the maximum point on the graph at around iron (Fe 56)

89
Q

what does fusion do in terms of binding energy per nucleon?

A

increases the binding energy per nucleon which means lots of energy is released during fusion

90
Q

what does fission do in terms of binding energy per nucleon?

A

fission is when large nuclei split in two, the nucleon numbers of the two new nuclei are smaller than the original nucleus , which means there is an increase in the binding energy per nucleon, so energy is also released during nuclear fission but much more is produced in fusion

91
Q

what is alpha absorbed by?

A

absorbed by paper of a few cm of air

92
Q

what is beta-minus absorbed by?

A

absorbed by 3mm of aluminium

93
Q

what is beta-plus absorbed by?

A

annihilated by electron - so virtually no range

94
Q

what is gamma absorbed by?

A

absorbed by many cm of lead, or several m of concrete

95
Q

when balancing decay equations, what must be conserved?

A

charge and nucleon number

96
Q

gamma radiation is emitted from what type of nuclei?

A

a nuclei with an excess of energy, an ‘excited’ nuclei

97
Q

what can the binding energy per nucleon graph be used to estimate?

A

the energy released from nuclear reactions

98
Q

what is induced nuclear fission?

A

induced nuclear fission occurs when a nucleus absorbs slow-moving neutrons and the resulting unstable nucleus undergoes a fission reaction to split into two smaller nuclei and a small number of neutrons, releasing energy

99
Q

what is a chain reaction?

A

a chain reaction is the sequence of nuclear reactions produced when an induced nuclear fission reaction triggers more than one further fission reaction

100
Q

what is a control rod?

A

a control rod is a rod that can be lowered up and down into the core of a nuclear reactor, absorb neutrons and slow down the chain reaction, they are usually made of boron (to control rate of fission)

101
Q

what is a moderator?

A

a moderator is a substance used in nuclear reactor which slows down neutrons so that they have a greater change of being absorbed by the fissile nuclear fuel (aids reaction), they are usually made of graphite but can be water too

102
Q

what does the word fission actually mean?

A

splitting up or breaking into parts/components

103
Q

what does the diagram look like for a fission reactor?

A

see page 221 textbook

104
Q

what are the three types of nuclear waste?

A

high level, intermediate level

105
Q

what are the three types of nuclear waste?

A

high level, intermediate level, low level

106
Q

what is high level nuclear waste?

A

produces large amounts of radiation, includes fuel rods removed from the core and waste resulting from the reprocessing of this fuel

107
Q

what is intermediate level nuclear waste?

A

intermediate level nuclear waste is material which has become radioactive because it has been in a nuclear reactor, for example the reactor’s metal cladding

108
Q

what is low level nuclear waste?

A

low level waste nuclear waste include items which are only slightly radioactive due to becoming contaminated with small amounts of radioactivity, such as cleaning materials and protective clothing

109
Q

why does high level nuclear waste need shielding?

A

high level waste produces heat as a result of the rapid decay of some of the short lived isotopes, so it needs cooling for a few years, as well as shielding to block radioactive emissions over many thousands of years while the longer half-life isotopes decay

110
Q

what are two main advantages of nuclear fusion?

A
  • no radioactive waste products are formed by the fusion process (unlike with fission)
  • there is a virtually unlimited supply of the raw materials, about 1% of seawater molecules have a deuterium atom in them (deuterium and tritium are the two isotopes used in fusion)
111
Q

what is nuclear fusion?

A

when two light nuclei can combine to create a larger nucleus

112
Q

why is a high temp and high pressure required for nuclear fusion?

A

fusion requires a high temp and pressure to give the nuclei enough kinetic energy to overcome to electrostatic repulsion and be close enough to fuse with with the nuclear strong force

113
Q

what are the problems associated with building and decommissioning nuclear power plants?

A

because of all the necessary safety precautions, building and decomissioning is very time-consuming and expensive

114
Q

why is a lot of energy released in nuclear fusion?

A

a lot of energy is released during nuclear fusion because the new, heavier nucleus has a much higher binding energy per nucleon (and so a lower total mass), the energy released helps to maintain the high temperatures needed for further fusion reactions

115
Q

why is nuclear fusion not currently a source of energy?

A

not efficient, any apparatus than it can induce fission requires much more electrical energy than it could produce, too expensive

116
Q

where does nuclear fusion often occur in naturally?

A

stars like our Sun

OCR A-Level Physics (24 decks)

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