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
what are the relative charges of:
- proton
- antiproton
- neutron
- antineutron
- electron
- positron
- neutrino
- antineutrino
- proton: +1
- antiproton: -1
- neutron: 0
- antineutron: 0
- electron: -1
- positron: +1
- neutrino: 0
- antineutrino: 0
what are antiparticles
each particle type has a corresponding antiparticle with the same mass but the opposite charge
what is a neutrino
symbol is v
mass and relative charge are 0
lepton
only take part in weak interactions
what is the symbol for an antiproton
_
p
whats the symbol for a positron
e+
what are hadrons
give examples
they are made up of quarks
eg. protons and neutrons
what does a neutron decay into
a proton, an electron and an antineutrino
what are leptons
give examples
they are fundamental particles (can’t be split into smaller particles)
eg. electrons and neutrinos
what’s the antiparticle of an electron
positron
what are quarks
they are the building blocks for hadrons like protons and neutrons
there are 6 flavours
what is the symbol and charge of the 3 anti-quarks, anti-up, anti-down and anti-strange?
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
what quarks are protons made of
2 up quarks and 1 down quark because
2/3 + 2/3 -1/3 = +1
what quarks are neutrons made of
1 up quark and 2 down quarks
2/3 + -1/3 + - 1/3
= 2/3 - 1/3 - 1/3 = 0
what are mesons
made of one quark and one anti-quark
what is the conservation of charge
in any particle reaction, the total charge after the reaction must equal the total charge before the reaction
identify the missing quark and name the particle
uus -> ?dd + u(d with a line on top)
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
what is einstein’s mass-energy equation and what does it mean
∆E = ∆mc^2
energy can turn into mass and mass can turn into energy
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.
∆E = ∆mc^2
=1.673 X10^-27 X (3 X 10^8)^2
= 1.51 X 10^-10 J
what nuclear forces are hadrons subject to?
what nuclear forces are leptons subject to?
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
what was the Rutherford alpha-scattering experiment
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
what conclusions did Rutherford conclude from the alpha scattering experiment with the alpha particles being sent through a thin gold foil
- 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
what is the actual charge of a proton
+1.6 X 10 ^-19 C
what is the diameter of an atom
0.1 nm
what is the diameter of a nucleus
a few femtometres
1 fm = 1 X 10^-15 m
what are the particles that make up the nucleus called
nucleons
what are the forces in the nucleus
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
what’s been discovered about the strong nuclear force
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
what does the graph that compares the electrostatic and strong nuclear force show
- 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
calculate the electrostatic, repulsive force between 2 protons using the equation:
F=q^2/(4πε_0 r^2 )
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
calculate the attractive force between 2 protons using the equation:
F = Gm^2/r^2
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
describe pair production with a proton
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
what conditions have to be there for a photon to undergo pair production
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
describe pair production with a photon
if a photon has the minimum energy equal to the energy of the 2 particles at rest it can produce an electron-positron pair
in photon pair production how do you calculate the minimum energy of the photon
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
in photon pair production, how do you calculate the maximum wavelength or the minimum frequency of the photon
use E = hc/wavelength = hf
E = 2mc^2
max wavelength = hc / 2mc^2 = h/2mc
min frequency = 2mc^2 / h
Calculate the minimum energy photon must have to produce an electron-positron pair
Calculate the minimum frequency of this photon
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
what is annihilation
when a particle meets an antiparticle, all the mass of them both gets converted to energy, in the form of a pair of photon.
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)
E = mc^2
=1.675X10^-27 X (3X10^8)^2
= 1.51 X 10^-10J
what is quark confinement
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
what is the proton number
what is its symbol
the number of protons in an atom’s nucleus
aka atomic number
symbol Z
what is the nucleon number
what is its symbol
aka mass number
symbol A
how many protons and neutrons are in the nucleus
what are isotopes
atoms with the same number of protons but different number of neutrons
this affects the stability of the nucleus
what does this equation mean
R = r_0A^1/3
nuclear radius = the constant r_0 X nucleon number ^ 1/3
how would you work out the mean nuclear density
density = mass / volume volume = 4/3πr^3
what does the constant r_0 equal
- 4 fm
1. 4X 10^-15 m
why is the weak nuclear force important in terms of quarks
it’s an interaction that can change one flavour of quark into another
define radioactive decay
when an unstable nucleus attempts to reach a more stable state through the release of excess energy
why is nuclear decay spontaneous
- 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
why is nuclear decay random
- cannot predict when particular nuclei in a sample will decay
- each nucleus in the sample has the same chance of decaying per unit time
what happens to the mass and atomic number during alpha decay
mass number decreases by 4
atomic number decreases by 2
what is an alpha particle
a helium nucleus
consists of 2 protons and 2 neutrons
how is a beta particle formed
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)
what happens to the mass and atomic number during beta minus decay
mass number doesn’t change
atomic number increases by 1
how could a nucleus become unstable
- too many neutrons
- too few neutrons
- too many nucleons (too heavy)
- too much energy in the nucleus
describe the two types of beta radiation
beta minus - electron with a negative charge is produced
beta plus - electron with a positive charge (positron) is produced
what is a positron and what happens when it collides with an electron
annihilation
their mass is converted into electromagnetic energy in the form of 2 gamma photons
create a quark model for beta minus decay
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
give examples of hadrons
what forces are they subject to
protons and neutrons
strong nuclear force and the weak nuclear force
what force are leptons subject to
weak nuclear force
what is background radiation
where does it come from
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
when investigating radiation, what precautions should you take
- 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
how do you measure the count rate of a radioactive source
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
what’s the decay equation for beta plus decay
proton -> neutron + positron + neutrino
what is being decayed in beta minus decay vs beta plus decay
beta minus is a neutron decaying
beta plus is a proton decaying
put beta plus decay in a quark model
uud -> udd +positron +neutrino
u -> d + positron + neutrino
what fundamental forces are involved in beta decay
The weak interaction is responsible for beta decay.
It changes one flavour of quark into another.
what is gamma radiation
how does it change the mass and atomic number
Does NOT change mass or atomic number
they are high frequency EM waves
describe the ability to penetrate matter for alpha, beta and gamma radiation
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
what is ionisation ability and which radiation is the most/least ionising
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)
describe the nature of alpha, beta plus, beta minus and gamma radiation
alpha - helium nucleus (2 protons and 2 neutrons)
beta minus - fast moving electron
beta plus - fast moving positron
gamma - high energy EM wave
describe the deflection due to E-fields in alpha, beta minus, beta plus and gamma radiation
alpha - slightly deflected towards negative charge
beta minus - greatly deflected towards positive charge
beta plus - greatly deflected towards negative charge
gamma - no deflection
describe the deflection due to B-fields in alpha, beta minus, beta plus and gamma radiation
alpha - deflection opposite to beta minus but not as great
beta - greatly deflected. minus and plus in opposite directions
gamma - no deflection
define half life
the time it takes for half the radioactive nuclei in a sample to decay
define decay constant
the probability that an individual nucleus will decay per unit time interval
define activity
the rate at which nuclei decay
units Bq which is equivalent to s^-1
what does the equation A = λN mean
activity = decay constant X number of undecayed nuclei
what does the equation A = A_0e^-λt mean
activity after time t = start activity X e^-decay constant X time
make sure units are in seconds
what does the equation N = N_0e^-λt mean
number of undecayed nuclei = start number of undecayed nuclei X e^-decay constant X time
what does the equation T_0.5 = ln2 / λ mean
half life = ln2 / decay constant
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
1Bq = 1s^-1
2mins = 120s
N = At
= 2.8X10^7 X 120 = 3.36 X 10^9
Assumption: the beta particles are emitted constantly
describe the technique of radioactive dating
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.
what are the limitations of radioactive dating
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
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
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
How do you date rocks?
why can’t you use carbon
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)
in nuclear reactions, what quantities must be conserved
proton number
nucleon number (mass number)
energy/mass
the mass of the constituent parts of the nucleus (protons and neutrons) is always ________ than the mass of the nucleus
greater
why is energy/mass conserved in nuclear reactions
work is done to separate the nucleons
this energy is converted into the gain in mass
define the unified atomic mass unit
unit of MASS (u)
one twelfth of the mass of an atom of carbon 12
in equation sheet
What does the equation E = mc^2 tell us about the relationship between the mass and energy of a system
The mass increases when energy is supplied to it
Energy is released when the mass decreases
what does mass defect mean
how do you work it out
reduction in mass
mass of individual nucleons - mass of nucleus
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
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
define binding energy
energy needed to separate neutrons and protons from the nucleus
what does the equation ∆E=∆mc^2 stand for in terms of binding energy
binding energy = mass defect X speed of light ^2
how do you work out binding energy per nucleon
binding energy of nucleus / number of nucleons
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
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
what does the graph look like for binding energy per nucleon (y axis) and mass number (x axis)
steep line upwards up until mass number = 56
then gradual line downwards
explain the binding energy graph
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
Explain why energy is released if 2 light nuclei combine to produce a heavier one. What is the process called?
this is nuclear fusion
If 2 light nuclei fuse, final binding energy per nucleon is greater than the original nuclei therefore energy is released
Explain why energy is released is a heavy nucleus splits into 2 lighter ones. What is this process called?
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
why doesn’t nuclear fission occur when the mass number is lower than 56 and fusion when the mass number is greater than 56?
The products will have a smaller binding energy per nucleon so would require an input of external energy.
in nuclear fission how many neutrons are released
2 or 3
why is nuclear fission said to have a 1-to-1 relationship
how the reaction controlled
1 neutron will get absorbed by 1 uranium nucleus
it is a controlled chain reaction
it is controlled by control rods made of boron
name 2 fissile materials
uranium-235
plutonium-239
why is a chain reaction formed in a fission reactor
the fission reactions produce neutrons which then induce other nuclei to fission, which produce more neutrons which induce more fission and so on
what is the importance of a moderator in a fission reactor
fuel rods need to be placed in a moderator to slow down and/or absorb neutrons
keeps reaction going at a steady rate
what is the critical mass in a fission reactor
the amount fuel you need for a chain reaction to continue at a steady rate
how do control rods control a nuclear fission chain reaction
what are they made of
they limit the number of neutrons in the reactor
they absorb neutrons so that the rate of fission is controlled
usually made of boron
what is the use of the coolant in a fission reactor
it transfers heat in the reactor
heat is transferred to another coolant, usually water, which produces steam
how is high level waste dealt with from a fission reactor
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.
why is a leak of radioactive material from a fission reactor dangerous for us and the environment
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
define thermal neutron
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)
what happens during nuclear fusion
what conditions have to be present in order for it to happen
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.
give an example of a nuclear fusion reaction that happens in the sun (hydrogen to helium)
2,1 H + 1,1 H -> 3,2 He + energy
(deuterium + hydrogen -> helium isotope + energy
why is lots of energy released during nuclear fusion
the new, heavier nucleus has a much higher binding energy per nucleon
what types of neutrons are needed to cause fission of uranium-235 and why
thermal neutrons because otherwise they are travelling too fast and bounce off
what’s the reaction when deuterium and tritium fuse
forms helium + neutron + energy
what extreme conditions exist in the sun to allow for fusion to happen
temperature of the core is very high (15 million kelvin)
extremely high density (150,000 kgm^-3)
define the decay constant
the probability of decay of a nucleus per unit time
