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A-Level Physics - OCR A > M6, C4 Nuclear and Particle Physics > Flashcards

M6, C4 Nuclear and Particle Physics Flashcards

atomic structure the nucleus particles and antiparticles quarks and antiquarks radioactive decay nuclear decay equations exponential law of decay half-life and radioactive dating binding energy nuclear fission and fusion fission reactors

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1
Q

what are the relative charges of:

  • proton
  • antiproton
  • neutron
  • antineutron
  • electron
  • positron
  • neutrino
  • antineutrino
A
  • proton: +1
  • antiproton: -1
  • neutron: 0
  • antineutron: 0
  • electron: -1
  • positron: +1
  • neutrino: 0
  • antineutrino: 0
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2
Q

what are antiparticles

A

each particle type has a corresponding antiparticle with the same mass but the opposite charge

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3
Q

what is a neutrino

A

symbol is v
mass and relative charge are 0
lepton
only take part in weak interactions

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4
Q

what is the symbol for an antiproton

A

_

p

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5
Q

whats the symbol for a positron

A

e+

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6
Q

what are hadrons

give examples

A

they are made up of quarks

eg. protons and neutrons

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7
Q

what does a neutron decay into

A

a proton, an electron and an antineutrino

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8
Q

what are leptons

give examples

A

they are fundamental particles (can’t be split into smaller particles)
eg. electrons and neutrinos

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9
Q

what’s the antiparticle of an electron

A

positron

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10
Q

what are quarks

A

they are the building blocks for hadrons like protons and neutrons
there are 6 flavours

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11
Q

what is the symbol and charge of the 3 anti-quarks, anti-up, anti-down and anti-strange?

A

anti-up: u with a line on top and a charge of -2/3e

anti-down: d with a line on top and a charge of +1/3e

anti-strange: s with a line on top and a charge of +1/3e

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12
Q

what quarks are protons made of

A

2 up quarks and 1 down quark because

2/3 + 2/3 -1/3 = +1

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13
Q

what quarks are neutrons made of

A

1 up quark and 2 down quarks
2/3 + -1/3 + - 1/3
= 2/3 - 1/3 - 1/3 = 0

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14
Q

what are mesons

A

made of one quark and one anti-quark

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15
Q

what is the conservation of charge

A

in any particle reaction, the total charge after the reaction must equal the total charge before the reaction

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16
Q

identify the missing quark and name the particle

uus -> ?dd + u(d with a line on top)

A

uus = 2/3 +2/3 - 1/3 = +1
?dd = ? - 1/3 -1/3 = ?-2/3
ud with a line on top = 2/3 + 1/3 = +1

+1 = ?-2/3 +1
? = +2/3
this is an up quark

the particle is therefore ‘udd’ which is a neutron

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17
Q

what is einstein’s mass-energy equation and what does it mean

A

∆E = ∆mc^2

energy can turn into mass and mass can turn into energy

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18
Q

The mass of a proton at rest is 1.673 X 10^-27 kg.

Calculate the energy that would be released if this proton were completely converted into energy.

A

∆E = ∆mc^2

=1.673 X10^-27 X (3 X 10^8)^2
= 1.51 X 10^-10 J

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19
Q

what nuclear forces are hadrons subject to?

what nuclear forces are leptons subject to?

A

all hadrons are subject to both the strong nuclear force and the weak nuclear force

all leptons are subject to the weak nuclear force but not the strong nuclear force

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20
Q

what was the Rutherford alpha-scattering experiment

A

a stream of alpha particles from a radioactive source was fired at a thin gold foil
flashes of light were produced and Geiger and Marsden counted these flashes
most alpha particles went straight through but a few scattered at angles greaters than 90 degrees

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21
Q

what conclusions did Rutherford conclude from the alpha scattering experiment with the alpha particles being sent through a thin gold foil

A
  • most of the alpha particles went straight through the foil so the atom is mainly empty space
  • some alpha particles were deflected through large angles so the centre of the atom must have a highly positive charge to repel them
  • very few particles were deflected by angles greater than 90 degrees so the nucleus must be tiny
  • most of the mass must be in the nucleus since the fast alpha particles were deflected backwards by the nucleus
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22
Q

what is the actual charge of a proton

A

+1.6 X 10 ^-19 C

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23
Q

what is the diameter of an atom

A

0.1 nm

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24
Q

what is the diameter of a nucleus

A

a few femtometres

1 fm = 1 X 10^-15 m

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25
Q

what are the particles that make up the nucleus called

A

nucleons

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26
Q

what are the forces in the nucleus

A

The electrostatic force which causes the positively charge protons to repel each other
The gravitational force which causes all the nucleons in the nucleus to attract each other due to their masses (this is tiny compared to the electrostatic force)

therefore there has to be another force called the strong nuclear force

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27
Q

what’s been discovered about the strong nuclear force

A

overcomes the electrostatic force
it has a short range - it can only hold nucleons together when they are separated by up to a few femtometres (the size of a nucleus)
the force is between all nucleons regardless of whether they are protons or neutrons

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28
Q

what does the graph that compares the electrostatic and strong nuclear force show

A
  • the strong nuclear force is repulsive for very small separations of nucleons (below 0.5fm)
  • as nucleon separation increases past 0.5 fm, the strong nuclear force becomes attractive. it reaches a max attractive value then falls rapidly to 0. after 3 fm it can no longer hold nucleons together
  • the electrostatic repulsive force extends over a much larger range
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29
Q

calculate the electrostatic, repulsive force between 2 protons using the equation:
F=q^2/(4πε_0 r^2 )

A 
ε_0 = 8.85 X 10^-12 (in equation sheet)
r = 2 X 10^-15m (because that is the distance between 2 protons approx.)

(1.6X10^-19)^2 / 4π X 8.85X10^-12 X (2X10^-15)^2

= 57.5 N

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30
Q

calculate the attractive force between 2 protons using the equation:
F = Gm^2/r^2

A 
G = 6.67 X 10^-11 (in equation sheet)
m = 1.673 X 10^-27 (mass of proton given in equation sheet)
r = 2 X 10^-15m (because that is the distance between 2 protons approx.)

6.67X10^-11 X (1.673X10^-27)^2 / (2X10^-15)^2
= 4.67 X 10^-35 N

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31
Q

describe pair production with a proton

A

If you fire two protons at each other at a high speed, you’ll end up with a lot of energy at the point of impact.

This energy might be converted into more particles

When energy is converted into mass you get equal amounts of matter and antimatter
eg. if an extra proton is formed then there will be an antiproton

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32
Q

what conditions have to be there for a photon to undergo pair production

A

one photon needs enough energy to produce that much mass (eg. a gamma ray photon)
tends to happen near a nucleus, which helps conserve momentum

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33
Q

describe pair production with a photon

A

if a photon has the minimum energy equal to the energy of the 2 particles at rest it can produce an electron-positron pair

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34
Q

in photon pair production how do you calculate the minimum energy of the photon

A

the particle and antiparticle have the same mass so it would equal 2M
E = mc^2
so the minimum energy of a photon would be:
E = 2mc^2

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35
Q

in photon pair production, how do you calculate the maximum wavelength or the minimum frequency of the photon

A

use E = hc/wavelength = hf
E = 2mc^2

max wavelength = hc / 2mc^2 = h/2mc

min frequency = 2mc^2 / h

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36
Q

Calculate the minimum energy photon must have to produce an electron-positron pair

Calculate the minimum frequency of this photon

A

mass of an electron and a positron= 9.11 X 10^-31
E = 2mc^2
= 2 X 9.11X10^-31 X (3X10^8)^2
= 1.64 X 10^-13 J

f = E / h
=1.64X10^-13 / 6.63X10^-34
= 2.47 X 10^20 Hz

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37
Q

what is annihilation

A

when a particle meets an antiparticle, all the mass of them both gets converted to energy, in the form of a pair of photon.

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38
Q

A neutron and antineutron collide and annihilate.
Calculate the minimum energy of one of the photons produced.

(mass of a neutron = 1.675 X 10^-27 kg)

A

E = mc^2

=1.675X10^-27 X (3X10^8)^2
= 1.51 X 10^-10J

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39
Q

what is quark confinement

A

you can’t get a quark by itself
if you blasted a proton with lots of energy, a single quark wouldn’t be removed
the energy that you supplied would just get changed into a quark-anti-quark pair

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40
Q

what is the proton number

what is its symbol

A

the number of protons in an atom’s nucleus
aka atomic number
symbol Z

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41
Q

what is the nucleon number

what is its symbol

A

aka mass number
symbol A
how many protons and neutrons are in the nucleus

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42
Q

what are isotopes

A

atoms with the same number of protons but different number of neutrons
this affects the stability of the nucleus

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43
Q

what does this equation mean

R = r_0A^1/3

A

nuclear radius = the constant r_0 X nucleon number ^ 1/3

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44
Q

how would you work out the mean nuclear density

A 
density = mass / volume
volume = 4/3πr^3
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45
Q

what does the constant r_0 equal

A
  1. 4 fm

1. 4X 10^-15 m

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46
Q

why is the weak nuclear force important in terms of quarks

A

it’s an interaction that can change one flavour of quark into another

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47
Q

define radioactive decay

A

when an unstable nucleus attempts to reach a more stable state through the release of excess energy

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48
Q

why is nuclear decay spontaneous

A
  • the decay of a particular nucleus is not affected by the presence of other nuclei
  • the decay of nuclei cannot be affected by chemical reactions or external forces eg. temperature & pressure
49
Q

why is nuclear decay random

A
  • cannot predict when particular nuclei in a sample will decay
  • each nucleus in the sample has the same chance of decaying per unit time
50
Q

what happens to the mass and atomic number during alpha decay

A

mass number decreases by 4

atomic number decreases by 2

51
Q

what is an alpha particle

A

a helium nucleus

consists of 2 protons and 2 neutrons

52
Q

how is a beta particle formed

A

very fast moving electron that is formed when a neutron decays
the neutron produces a proton and a electron
the proton is held in the nucleus but the electron is ejected (making a beta particle)

53
Q

what happens to the mass and atomic number during beta minus decay

A

mass number doesn’t change

atomic number increases by 1

54
Q

how could a nucleus become unstable

A
  • too many neutrons
  • too few neutrons
  • too many nucleons (too heavy)
  • too much energy in the nucleus
55
Q

describe the two types of beta radiation

A

beta minus - electron with a negative charge is produced

beta plus - electron with a positive charge (positron) is produced

56
Q

what is a positron and what happens when it collides with an electron

A

annihilation

their mass is converted into electromagnetic energy in the form of 2 gamma photons

57
Q

create a quark model for beta minus decay

A

udd -> uud + (the electron is fundamental so isn’t made of quarks
the ud can cancel on both sides

so
d -> u + e^- + anti-electron neutrino

58
Q

give examples of hadrons

what forces are they subject to

A

protons and neutrons

strong nuclear force and the weak nuclear force

59
Q

what force are leptons subject to

A

weak nuclear force

60
Q

what is background radiation

where does it come from

A

low level of radiation that surrounds us at all times

made from naturally occurring isotopes, cosmic radiation from space and man-made sources from industry or medicine

61
Q

when investigating radiation, what precautions should you take

A
  • radioactive substance should be kept in a lead-lined box when not being used
  • only pick up radioactive substance using long-handled tongs or forceps
  • do not point substance at anyone and keep a safe distance away
62
Q

how do you measure the count rate of a radioactive source

A

1) calculate the background count rate over 30s
2) Place radioactive source in front of Geiger-Muller tube so a high number of counts are detected
3) Take 3 sets of count measurements for three 30s intervals and find the mean
4) Subtract the background count rate from the value to get the count rate of the source

63
Q

what’s the decay equation for beta plus decay

A

proton -> neutron + positron + neutrino

64
Q

what is being decayed in beta minus decay vs beta plus decay

A

beta minus is a neutron decaying

beta plus is a proton decaying

65
Q

put beta plus decay in a quark model

A

uud -> udd +positron +neutrino

u -> d + positron + neutrino

66
Q

what fundamental forces are involved in beta decay

A

The weak interaction is responsible for beta decay.

It changes one flavour of quark into another.

67
Q

what is gamma radiation

how does it change the mass and atomic number

A

Does NOT change mass or atomic number

they are high frequency EM waves

68
Q

describe the ability to penetrate matter for alpha, beta and gamma radiation

A

alpha - 1 sheet of paper, a few cm of air or skin

beta - approx. 1m of air or a few mm of aluminium

gamma - approx., a few cm of lead or several m of concrete

69
Q

what is ionisation ability and which radiation is the most/least ionising

A

ionisation ability - the ability to knock electrons off an atom

alpha - highly ionising
beta- moderate (low mass:charge ratio)
gamma - very low (has no charge and no mass)

70
Q

describe the nature of alpha, beta plus, beta minus and gamma radiation

A

alpha - helium nucleus (2 protons and 2 neutrons)
beta minus - fast moving electron
beta plus - fast moving positron
gamma - high energy EM wave

71
Q

describe the deflection due to E-fields in alpha, beta minus, beta plus and gamma radiation

A

alpha - slightly deflected towards negative charge
beta minus - greatly deflected towards positive charge
beta plus - greatly deflected towards negative charge
gamma - no deflection

72
Q

describe the deflection due to B-fields in alpha, beta minus, beta plus and gamma radiation

A

alpha - deflection opposite to beta minus but not as great

beta - greatly deflected. minus and plus in opposite directions

gamma - no deflection

73
Q

define half life

A

the time it takes for half the radioactive nuclei in a sample to decay

74
Q

define decay constant

A

the probability that an individual nucleus will decay per unit time interval

75
Q

define activity

A

the rate at which nuclei decay

units Bq which is equivalent to s^-1

76
Q

what does the equation A = λN mean

A

activity = decay constant X number of undecayed nuclei

77
Q

what does the equation A = A_0e^-λt mean

A

activity after time t = start activity X e^-decay constant X time

make sure units are in seconds

78
Q

what does the equation N = N_0e^-λt mean

A

number of undecayed nuclei = start number of undecayed nuclei X e^-decay constant X time

79
Q

what does the equation T_0.5 = ln2 / λ mean

A

half life = ln2 / decay constant

80
Q

a radioactive source emits beta particles
it has activity of 2.8X10^7 Bq
estimate the number emitted in the time interval 2 mins

state one assumption made

A

1Bq = 1s^-1
2mins = 120s
N = At
= 2.8X10^7 X 120 = 3.36 X 10^9

Assumption: the beta particles are emitted constantly

81
Q

describe the technique of radioactive dating

A

High speed protons in cosmic rays from space collide with atoms in the upper atmosphere to produce neutrons.
These neutrons collide with nitrogen-14 nuclei in the atmosphere to form carbon-14 nuclei.
C-14 eventually emit beta minus particles and become N-14 again so amount of N-14 in the atmosphere is replenished.

82
Q

what are the limitations of radioactive dating

A

assumes ratio of C14 atoms to C12 atoms remains constant over time
increased emission of CO2 may have reduced the ratio as would other events such as volcanic eruptions, nuclear weapon testing and nuclear disasters

83
Q

the half life of an isotope is 60 minutes. Calculate how long it takes for the activity to fall to 70% of its original value

A 
let A_0 = 1 
so A = 0.7

λ = ln2 / 60 = 0.01155

A=A_0e^-λt
0.7 = e^-0.01155t
ln0.7 = -0.01155t
t = 30.87
= 31 mins
84
Q

How do you date rocks?

why can’t you use carbon

A

Can’t use carbon because it’s half life isn’t long enough

Instead you use Rb-87 which emits beta minus and decays to stable Sr-87 (strontium)

(the half life for Rb is 49 billion years)

85
Q

in nuclear reactions, what quantities must be conserved

A

proton number
nucleon number (mass number)
energy/mass

86
Q

the mass of the constituent parts of the nucleus (protons and neutrons) is always ________ than the mass of the nucleus

A

greater

87
Q

why is energy/mass conserved in nuclear reactions

A

work is done to separate the nucleons

this energy is converted into the gain in mass

88
Q

define the unified atomic mass unit

A

unit of MASS (u)
one twelfth of the mass of an atom of carbon 12

in equation sheet

89
Q

What does the equation E = mc^2 tell us about the relationship between the mass and energy of a system

A

The mass increases when energy is supplied to it

Energy is released when the mass decreases

90
Q

what does mass defect mean

how do you work it out

A

reduction in mass

mass of individual nucleons - mass of nucleus

91
Q 
Calculate the mass defect of a helium nucleus
It's made of 2 protons and 2 neutrons 
u = 1.661 X 10^-27
mass of proton = 1.673 X 10^-27 kg
mass of neutron = 1.675 X 10 ^-27 kg
A

mass of nucleus = (protons+neutrons)u
= 4 X 1.661X10^-27 = 6.644 X 10^-27

mass of nucleons
2 X protons = 2 X 1.673 X 10^-27 = 3.346 X 10^-27
2 X neutrons = 2 X 1.675 X 10^-27 = 3.35 X 10^-27
mass of nucleons = 3.346 X 10^-27 + 3.35 X 10^-27 = 6.696 X 10^-27 kg

mass defect = 6.696 X10^-27 - 6.644 X 10^-27 = 5.2 X 10^-29 kg

92
Q

define binding energy

A

energy needed to separate neutrons and protons from the nucleus

93
Q

what does the equation ∆E=∆mc^2 stand for in terms of binding energy

A

binding energy = mass defect X speed of light ^2

94
Q

how do you work out binding energy per nucleon

A

binding energy of nucleus / number of nucleons

95
Q

Calculate the binding energy per nucleon for Iron in mega electronvolts. It has 26 protons and 30 neutrons.
mass of neutron = 1.675 X 10^-27 kg
mass of proton = 1.673 X 10^-27 kg
mass of iron nucleus = 9.288 X 10^-26

A

Mass of nucleons = (26 X 1.673 X10^-27) + (30 X 1.675 X10^-27) = 9.3748 X 10^-26

mass defect = 9.3748X10^-26 - 9.288X10^-26 = 8.68X10^-28 kg

binding energy = 8.68X10^-28 X (3X10^8)^2 = 7.812 X10^-11 J

there are 56 nucleons so binding energy per nucleon = 7.812X10^-11 / 56 = 1.4 X10^-12 J

= 8.7 MeV

96
Q

what does the graph look like for binding energy per nucleon (y axis) and mass number (x axis)

A

steep line upwards up until mass number = 56

then gradual line downwards

97
Q

explain the binding energy graph

A

the first part of the graph which is increasing is nuclear fusion
this leads up to mass number of 56 which is iron. this is the most stable isotope.
the downwards part of the graph is nuclear fission. the arrow points upwards to 56Fe

energy is released in both nuclear fission and fusion

98
Q

Explain why energy is released if 2 light nuclei combine to produce a heavier one. What is the process called?

A

this is nuclear fusion
If 2 light nuclei fuse, final binding energy per nucleon is greater than the original nuclei therefore energy is released

99
Q

Explain why energy is released is a heavy nucleus splits into 2 lighter ones. What is this process called?

A

this is nuclear fission
A large nucleus splits into 2 fragments which have a greater binding energy per nucleon than the original nucleus so again energy is released

100
Q

why doesn’t nuclear fission occur when the mass number is lower than 56 and fusion when the mass number is greater than 56?

A

The products will have a smaller binding energy per nucleon so would require an input of external energy.

101
Q

in nuclear fission how many neutrons are released

A

2 or 3

102
Q

why is nuclear fission said to have a 1-to-1 relationship

how the reaction controlled

A

1 neutron will get absorbed by 1 uranium nucleus

it is a controlled chain reaction
it is controlled by control rods made of boron

103
Q

name 2 fissile materials

A

uranium-235

plutonium-239

104
Q

why is a chain reaction formed in a fission reactor

A

the fission reactions produce neutrons which then induce other nuclei to fission, which produce more neutrons which induce more fission and so on

105
Q

what is the importance of a moderator in a fission reactor

A

fuel rods need to be placed in a moderator to slow down and/or absorb neutrons
keeps reaction going at a steady rate

106
Q

what is the critical mass in a fission reactor

A

the amount fuel you need for a chain reaction to continue at a steady rate

107
Q

how do control rods control a nuclear fission chain reaction

what are they made of

A

they limit the number of neutrons in the reactor
they absorb neutrons so that the rate of fission is controlled
usually made of boron

108
Q

what is the use of the coolant in a fission reactor

A

it transfers heat in the reactor

heat is transferred to another coolant, usually water, which produces steam

109
Q

how is high level waste dealt with from a fission reactor

A

These products are very hot and highly radioactive.

The material is placed in a cooling pond until the temp falls to a safe level. It’s then stored in sealed containers in specialist facilities which are deep underground. It’s kept there until its activity has fallen sufficiently for it to be considered safe.

110
Q

why is a leak of radioactive material from a fission reactor dangerous for us and the environment

A

it could enter our water supply and food chain
if radiation reaches a cell it can ionise atoms inside it which can kill the cell
it can also cause a mutation in the cell’s DNA which can result in cancer

111
Q

define thermal neutron

A

a neutron in a nuclear reactor that has been slowed down enough by a moderator that it can be captured by uranium nuclei (or other fissionable nuclei)

112
Q

what happens during nuclear fusion

what conditions have to be present in order for it to happen

A

Two nuclei combine to make a larger nucleus.
The nuclei have to be moving very fast to overcome the electrostatic repulsion between them and get close enough for the strong interaction to bind them.
This means there has to be much higher temperatures and higher pressures.

113
Q

give an example of a nuclear fusion reaction that happens in the sun (hydrogen to helium)

A

2,1 H + 1,1 H -> 3,2 He + energy

(deuterium + hydrogen -> helium isotope + energy

114
Q

why is lots of energy released during nuclear fusion

A

the new, heavier nucleus has a much higher binding energy per nucleon

115
Q

what types of neutrons are needed to cause fission of uranium-235 and why

A

thermal neutrons because otherwise they are travelling too fast and bounce off

116
Q

what’s the reaction when deuterium and tritium fuse

A

forms helium + neutron + energy

117
Q

what extreme conditions exist in the sun to allow for fusion to happen

A

temperature of the core is very high (15 million kelvin)

extremely high density (150,000 kgm^-3)

118
Q

define the decay constant

A

the probability of decay of a nucleus per unit time

A-Level Physics - OCR A (20 decks)

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