Particles and Radiation Flashcards
(22 cards)
Define the proton number (Z) and nucleon number (A)
Proton number: the number of protons in an atom (in a neutral atom the number of electrons is equal to the proton number)
Nucleon number: the number of nucleons in an atom (protons + neutrons)
List the particles that make up the atom and give their charges and relative masses
Proton: charge of +1, relative mass of 1.
Neutron: no charge, relative mass of 1.
Electron: charge of -1, relative mass of 0.0005.
What is an isotope?
An atom with the same number of protons but a different number of neutrons
Properties:
Same chemical properties;
More unstable, may even be radioactive and decay to make themselves stable
What causes an electrostatic force inside the nucleus?
The like-charged protons repelling each other
What evidence suggests the existence of a strong nuclear force?
As if only electrostatic forces and gravity were responsible for the formation of nuclei, no nuclei could form as they are not sufficiently attractive. Therefore, another attractive force must be in play that holds nuclei together - the strong nuclear force.
Is the strong interaction attractive or repulsive at a nucleon separation of 10 fm?
Negligible The strong force is: Repulsive up to 0.5 fm Attractive from 0.5 fm to 3/4 fm (peaking at 1.5 fm) Negligible beyond 3/4 fm
Describe the changes that happen in the nucleus during alpha and beta-minus decay
Alpha decay: the proton number decreases by two and the nucleon number decreases by four
Beta-minus decay: the proton number increases by one and the nucleon number stays the same (a neutron becomes a proton and an electron-antineutrino is released)
Describe the properties of an electron-antineutrino
Zero or almost zero mass
Zero charge
Don’t do much, they only take part in weak interactions
What is pair production?
Pair production is the production of a particle-antiparticle pair from energy
Key points:
Pair production only happens if one gamma ray photon has enough energy to produce the required mass.
It also trends to happen near a nucleus, which helps conserve momentum.
Typically electron-positron pairs are produced as they have a relatively low mass.
(The particle tracks are curved in opposite directions as there is a magnetic field present and they have opposite charges)
What happens when a proton collides with an antiproton?
Annihilation.
Their masses are converted back into energy in the form of two gamma ray photons
List the differences between a hadron and a lepton
Leptons are fundamental, hadrons are comprised of quarks
Leptons don’t feel the strong nuclear force and interact through the weak
Which is the only stable baryon (probably)?
The proton.
The proton is the only stable baryon as all other baryons decay
What the baryons end up as depends on what it started off as but it always includes a proton
A particle collision at CERN produces 2 protons, 3 pions and 1 neutron.
What is the total baryon number of these particles?
2 protons= +2
3 pions= 0
1 neutron= +1
Total = +3
Which two particles have a lepton tau number of +1?
Tau and tau-neutrino
What is a quark?
Quarks are the fundamental particles that make up hadrons
Which type of particle is made from a quark and an antiquark?
Mesons (pions, kaons…)
Describe how a neutron is made up from quarks
The neutron is made of an up, and two down quarks
List four quantities that are conserved in particle interactions
Charge
Baryon number
Strangeness (in strong interactions)
Lepton number (conserved discretely by generation)
List the four fundamental forces in nature
Name: gauge boson; particles affected.
Gravity: graviton; all types.
Electromagnetic: photon; charged particles.
Strong nuclear force: gluon; hadrons only.
Weak nuclear force: W+, W-, Z; all types.
Explain what a virtual particle is
Gauge bosons, they only exist for a short time (undetectable).
Draw the Feynman diagram for a beta-minus decay interaction
_
n –> p + e- + V
(Neutron and proton on the left, electron and electron-antineutrino on the right, gauge boson W- from left to right)
Which gauge bosons are exchanged in weak interactions?
W+, W-, Z
