Particle Physics Flashcards
The 3 conservation laws observed in nuclear reactions
Conservation of mass - energy
Conservation of momentum
Conservation of charge
Law of conservation of mass - energy
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
Law of conservation of momentum
in any interaction between two particles in a closed system the total momentum before the interaction ewuals the total momentum after the interaction
Law of conservation of charge
In a nuclear reaction the total amount of electric charge before the reaction equals the total amount of electric charge after the reaction
normal unit of energy
joule
J
teeny tiny unit of energy
eV
electron volt
1 eV =
1.6 x 10^-19 joules
1 keV =
1 x 10^3
1 MeV =
1 x 10^6
1 GeV =
1 x 10^9
what page in the maths tables can you find milli, kilo, giga etc.
pg 45
normal unit of mass
kg
teeny tiny unit of mass
u
u
unified atomic mass unit
where can you find the charge on the electron (same as eV to joule)
pg 46
where can you find the conversion of u to kg
pg 47 of the maths tables
how to find the energy of a mass converted to energy
E = mc squared
put everything in joules and then kg and then convert back if asked for it
how to calculate the energy released in a nuclear equation
mass of first nucleus - (mass of second nucleus + mass of emitted particle) = m
e = mc squared
where does most of the kinetic energy released in a nuclear equation go?
as kinetic energy
how do you get the ratio of kinetic energies
kinetic energy 1 / kinetic energy 2
what should get nearly all of the energy
the smallest particle
if the momentum of the electron (beta particle) differs before and after, what is needed
a new particle, the neutrino
who proved that E=mc squared
walton and Cockcroft
walton and Cockcroft experiment
they bombarded lithium with protons
walton and Cockcroft experiment: first thing they did
protons were produced in a hydrogen discharge tube and were fed into an accelerator tube
walton and Cockcroft experiment: what accelerated the protons?
a voltage of the order 700,000
walton and Cockcroft experiment: how did the protons hit the lithium target?
at an angle of 45º
walton and Cockcroft experiment: how were the particles emitted?
in opposite directions at right angles to the protons
walton and Cockcroft experiment: what did the emitted particles cause?
scintillations at a fluorescent screen
walton and Cockcroft experiment: how were the scintillations observed?
with the help of a microscope
walton and Cockcroft experiment: what were the emitted particles?
nuclei of helium (alpha particles)
walton and Cockcroft experiment: equation
L7 + H -> He + He + energy
walton and Cockcroft experiment: what was noted about the energies
the energy of the emitted alpha particles was far greater than the energy of the incoming protons
walton and Cockcroft experiment: what did the inconsistency in energies show?
that energy had been obtained from mass
transmutation
changing one element into another
who performed the first transmutation and equation
rutherford
He + N14 -> O27 + H
walton and Cockcroft experiment: what achievement did they carry out?
the first transmutation using artificially accelerated particles
what does a linear accelerator do?
it successively accelerates electrons as they pass through a set of cylindrical electrodes
linear accelerator: what is applied to the electrodes
an alternating current is applied to each electrode so that it is positive as electrons approach and negative as electrons leave it
linear accelerator: where are the electrons accelerated?
at the gaps
when does the length of an accelerator not need to be so long?
when particles are allowed to follow a circular path
cyclotron: how do the particles move?
a magnetic field is applied perpendicularly to the 2 semi circular shaped cavities in which the charged particles will move
cyclotron: what happens when the charged particle from the source enters the magnetic field?
it follows a circular path
cyclotron: how do you ensure that the particle accelerates each time it crosses the gap?
an alternating voltage is applied across the 2 semi circles
cyclotron: what happens as the charged particle gains speed
the radius of its circular motion increases and it spirals outwards from the source
cyclotron: equation for radius
r = mv/Bq
what happens when the charged particle gets to the edge of the cyclotron
it leaves and gets fired at its target
2 advantages of circular accelerators
- they are more compact than linear accelerators
- they accelerate particles at higher speeds than linear particles do
if the reaction takes place in a cloud chamber?
a magnetic field will cause the 2 particles (1 is charged negatively and one is charged positively) to be deflected in opposite directions
what happens when high energy Ɣ rays are fired at a sheet of lead
an electron and a positron are produced
explain this: when high energy Ɣ rays are fired at a sheet of lead an electron and a positron are produced
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
pair production equation
hf = m1 c squared + m2 c squared + E1 + E2
2 things that are conserved in the reaction of pair production
charge and momentum
explain how charge is conserved in the reaction of pair production
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
each particle has
an antiparticle; eg. an antiproton
symbol for antiparticle
a bar over the particle
if a particle has a charge
its antiparticle has an opposite charge
why are antiparticles difficult to detect
because when a particle meets its antiparticle both are annihilated and the mass of the particles turns to energy
where are positrons and antiprotons kept at CERN
in circular evacuated containers and are kept in place using magnetic fields
what is pair annihilation the reverse of?
pair production
an example of pair annihilation
e+ + e- -> y + y
2 things that are conserved in pair annihilation
momentum and charge
how do we know that momentum is conserved in pair annihilation?
its the reason why 2 photons are produced and travel in opposite directions
what are pair production and pair annihilation examples of?
the equivalence of mass and energy as predicted by Einstein
where can pair annihilation be used?
in the study of brain abnormalities
diagnostic technique of studying brain abnormalities
positron emission tomography (PET)
explain PET
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
gravitational force
an attractive force that is hardly noticeable unless the masses in question are quite large e.g. planets
Newton’s law of gravitational force
the magnitude of the force is inversely proportional to the square of the distances between the centres of the 2 masses
equation for Newton’s law of gravitational force
F = Gm1m2 / d squared
over what distance does gravitational force act?
over infinite distance
effect of gravitational force in particles around the nucleus
negligible
what is currently believed that transmits gravitational force
a particle; the graviton
Part of the electrostatic force between 2 charges is given by what?
coulumb’s law
Coulumb’s Law
F = q1q2/4pied squared
is the electrostatic force attractive or repulsive
can be either depending on the sign of the charges
the second part of the electromagnetic force is?
the magnetic force between moving charges
function of the magnetic force between moving charges in our lives
it is the force that binds electrons and protons together and that binds atoms together to form matter
does the the magnetic force between moving charges obey the inverse square law?
yes
when does the magnetic force between moving charges decline
with distance
range of the magnetic force between moving charges
infinite
what is believed about how the electromagnetic force is transmitted
by the exchange of photons
the strongest of the 4 forces
the strong nuclear force
function of the strong nuclear force
holds the protons and neutrons together in the nucleus
what would happen in the nucleus if the strong force wasn’t there
the positive protons would repel
range of the strong force
10 ^ -15 m
does the electron experience the strong force?
no
what must the strong force also be?
must be sufficiently repulsive to prevent the nucleus from collapsing in on itself
for the strong force, what are the messenger particles called?
gluons
what do gluons do?
they transmit the strong force between elementary particles
who experiences the weak nuclear force?
all particles
range of the weak nuclear force
10 ^-18 m
how does the neutrino interact with matter?
via the weak force
example of neutrino interacting with matter via the weak force and equation
an antineutrino and a proton interact to produce a positron and a neutron
-v- + p -> n + e+
what shows that weak interactions have a low probability of happening
a neutrino can pass through the earth without interacting
what is the weak force responsible for?
the conversion of neutrons to protons in the process of beta decay in radioactivity
what is proposed about the weak force?
that it is transmitted by photons and massive W-particles and X-particles?
forces in order of descending relative strength
strong nuclear
electromagnetic
weak nuclear
gravitational
strong nuclear affects
proton, neutron, quark
weak nuclear affects
all particles
electromagnetic affects
charged particles
gravitational affects
all particles
criterion for the order on which they put the particles from the particle zoo
whether or not they feel the nuclear force
leptons
affected by the weak force nut not the strong force
hadrons
hadrons are affected by both the strong force and the weak force
6 leptons
electron neutrino muon tau muon neutrino tau neutrino
2 groups of hadrons
baryons
mesons
what forces can leptons and hodrons be affected by as well as strong force
gravitational force, and if charged the electromagnetic force
what does evidence suggest at the moment about leptons
that they are elementary particles
elementary particles
cannot be subdivided into small particles
baryons’ mass
similar to or greater than that of the proton
mesons’ mass
less than than of the baryon but greater than that of leptons
are baryons and mesons fundamental particles
no
what are baryons and mesons composed of
quarks
quarks
the elementary particles that make up baryons and mesons
first 3 quarks discovered
up (u) down (d) and strange (s)
other 3 quarks
charm (c), top(t) and botto (b)
quarks’ charges
1/3 or 2/3
how many antiquarks are there?
6
why is it very difficult to isolate a quark
they feel all 4 forces but principally the strong nuclear force
what is a meson made up of?
any one quark and any one antiquark
what are baryons made up of?
any 3 quarks and antibaryons are made up of any 3 antiquarks
what are now believed to be the fundamental constituents of matter?
the 6 quarks and the 6 leptons
