atomic, nuclear and particle Flashcards
what does the bohr model show
if the angular momentum was quantized the electrons of hydrogen would have discrete energy levels, giving the observed spectral lines.
failures of bohr model
Failed to predict the varying intensity or fine detail of hydrogen lines and failed to derive correct energy levels for other atoms
mass-energy equivalence
As the mass of an electron and positron can be converted into the energy of gamma radiation, mass and energy must be equivalent
mass of an electron
0.5 MeV
1u in MeV
1 u = 931.5 MeV
proton mass in kg and u
- 673 × 10–27kg
1. 007 28u
quantize definition (no need memrise)
form into quanta, in particular restrict the number of possible values of (a quantity) or states of (a system) so that certain variables can assume only certain discrete magnitudes.
“light is quantized into packets of energy”
whats a quantum
a discrete packet of energy, charge, or any other quantity.
exam electron definition
fundamental particle with a charge of -1.6x10^-9 and mass of 9.1x10^-31
antimatter
matter made of negative protons (antiprotons) and positive electrons (positrons)
antiparticles
for every particle there is an antiparticle which has the same mass but opposite charge
what happens if a particle meets its antiparticle
they annihilate each other, turning into high energy photons
amount of energy given out as photons if an electron annihilates a positron
1.22 MeV
unit of atomic mass (u)
1u is defined as the mass of 1/12 of an atom of a carbon-12 atom
nucleon number(A)
same as atomic mass number
number of protons + neutrons
what defines the charge of the nucleus
the proton number (Z)
Isotopes
nuclides with same proton number but different nucleon numbers
approx energy to remove an electron from an atom
~1eV of energy
b/c the energy of an atomic electron is in the region of -1eV
binding energy of a nucleus
the energy required to pull the nucleus apart - or amount of energy released when the nucleus is put together
conversion from u (mass unit) to MeV
first convert to joules using E = mc^2, then to get to MeV divide by fundamental charge
alpha emission
when two protons and two neutrons leave the nucleus as one particle, called an alpha particle (identical to a helium nucleus)
beta emission
when a neutron decays to a proton and an electron inside the nucleus
the high energy electron leaves the nucleus as a beta particle
Gamma emission
when the nucleus emits a short burst of high-energy electromagnetic radiation
why gamma radiation is different to alpha and beta
when alpha and beta particles are emitted the nucleus changes into a different element
when gamma rays are emitted the element does not change
what are beta minus particles and how are they formed
They’re electrons formed when a neutron changes to a proton
When this happens an antineutrino is also produced
What’s a beta plus and when is it formed
It’s a positron, emitted from the nucleus when a proton changes to a neutron
unit for activity
becquerels (emissions per second)
what is tunnelling
alphas can get out of the nucleus without going over the potential barrier that holds the nucleons in place
half life
the time taken for half the number of unstable nuclei to decay (or activity to halve).
activity (A)
the number of decays per second
background radiation
radiation of environment, rocks, air, and from the Sun
decay constant
the probability of decay in one second. Gives the rate of decay for a given number of nuclei
fusion
The joining of small nuclei to make bigger ones with the release of energy.
fission
The splitting of large nuclei into smaller ones with the release of energy
baryon
made of 3 quarks (e.g. proton uud, neutron ddu)
meson
made of a quark + antiquark pair (e.g. pi meson)
confinement
the force required to pull quarks apart is so big that enough energy is transferred to the quarks to produce more quarks so single quarks cannot be observed.
pauli exclusion principle
particles with spin 1/2 cannot occupy the same energy state.
colour charge
property of quarks that causes them to experience the strong inter-quark force or ‘colour force’
why is antiblue drawn as yellow
because yellow and blue = white
anti-red
cyan
anti-green
magenta
what’s a gluon
the exchange particle of the colour force
the line spectrum for hydrogen gives evidence for
the existence of electron energy levels
absorption spectrum
when you take white light and pass it through an elemental gas (eg light from the sun through the atmosphere)
why use gold foil rutherford
gold sheets are only a few atoms deep, so produce results of interactions that could be best related to the interaction between a single alpha and a single nucleus
If the foil was too thick the alpha particles would just be absorbed
why vacuum rutherford
air would absorb the alpha particles before they hit the foil or before they got to the screen
why does the scintillation screen have a phosphorous coating rutherford
fluoresces (gives out a photon of visible light) when it is hit by a charged particle. Covering the microscope lens with ZnS allowed the viewer to ‘see’ where the alpha particles hit (or at least count their impacts)
weak force mediator
mediator: W-bosons (W+, W-, Z+)
particle: quark (mesons)
strong force mediator
mediator: gluons
particle: quark (baryons)
electromagnetic force mediator and particles
mediator: photons
particle: leptons
exchange particle involved in force between nucleons (nuclear force), and its mass
pion, mass 110MeVc^-2
nuclear force differences from electric force
force much stronger than electric force and has v short range
lepton number
+1 for leptons and -1 for antileptons
2 examples of leptons
electrons and neutrinos
2 examples of hadrons
neutrons and protons (so nucleons)
baryon number
+1 for baryons and -1 for antibaryons, 0 for mesons and leptons
charge number
the charge of the particle in multiples of e
spin number for baryons and mesons
1/2 or 1+1/2 for baryons
0 or 1 for mesons
strangeness
an extra quantum number that is not conserved in weak interactions
what doesn’t the standard model explain?
gravity or the existence of the dark matter and energy which is thought to make up 96% of the universe
‘external’ products of beta minus decay
beta minus particle (electron) and antineutrino
what does the wavy line in a feynman diagram represent?
an exchange particle
neutrino charge
zero
whats the force between quarks
strong force
unstable nucleus
nucleus that randomly and spontaneously emits particles that carry energy away from the nucleus
radioactivity
emission of particles and energy from a nucleus
emission spectrum definition
set of possible wavelengths that can be emitted by a gas
decay series
set of decays that takes place until a given nucleus ends up as a stable nucleus
what does it mean when we say decay is spontaneous
cannot affect the rate of decay of a given sample in any way
biding energy per nucleon for hydrogen
zero because only one particle in the nucleus
law of radioactive decay
rate of decay is proportional to the number of nuclei that have not yet decayed
consequence of law of radioactive decay
number of radioactive nuclei decreases exponentially
what are the three classes of elementary particles
quarks, leptons and exchange particles
lepton 3 types
electron, muon, tau (and their neutrinos)
higgs particle
responsible, through its interactions, for the mass of particles of the standard model, in particular the masses of W and Z
2 feynman diagram conventions
- time goes left to right
- real particles forward and antiparticles backward
all leptons have same charge
leptons have charge of -1
protons and neutrons held in the nucleus by
strong nuclear force
nuclide
nucleus characterized by specified number of protons and neutrons
what causes dark lines in the atomic spectra
when photons are absorbed
because they excite atomic electrons into higher energy levels
what does the standard model tell us
6 quarks, 6 leptons & 4 force carriers are all there is in the universe
how to distinguish which boson involved in a weak interaction
w+ and w- involved in interactions where there is exchange of charge, z involved when there is no exchange of charge
purpose of calculating binding energy per nucleon
- binding energy gives the amount of energy required to remove one nucleon from the nucleus giving an indication of its relative stability
- per nucleon in order to make comparisons between different nuclei
equipment used to measure the change in activity of an isotope over a period of time
GM tube
