Particle Physics Flashcards
(46 cards)
Who discovered the neutron and how?
James Chadwick discovered the neutron by shooting alpha particles at a sheet of beryllium and a paraffin block. The alpha particles knocked off neutrons off the beryllium, which in turn knocked off protons (H⁺) which were detected by the Geiger counter.
What conclusions were made from the experiment that proved the existence of the neutron?
If the particle can remove H⁺ it must be the same mass
It has neutral charge because it wasn’t detected by a magnet
What is the equation for specific charge?
Specific charge (C kg⁻¹) = charge / mass
What are the forces in a nucleus and where are their differences?
Strong force
Convert metres and femtometres
1 fm = 1*10⁻¹⁵ m
1 m = 1*10¹⁵ fm
What is the equation for the alpha decay of ²²⁶₈₈Ra?
²²⁶₈₈Ra –> ²²²₈₆Rn + ⁴₂He²⁺
What is the equation for the beta decay of ²¹⁰₈₃Bi?
²¹⁰₈₃Bi –> ²¹⁰₈₄Po + ⁰₋₁β + ⁰₀v̅ₑ
What is the difference between beta plus and beta minus decay?
beta minus (β⁻) decay: a neutron is converted to a proton and the process creates an electron and an electron antineutrino
beta plus (β⁺) decay: a proton is converted to a neutron and the process creates a positron and an electron neutrino
What is a proton or neutron inside the nucleus known as?
Nucleon
Discovery of the proton
Rutherford fired alpha particles at nitrogen. Protons were emitted and attracted to the cathode, causing a hydrogen red glow.
¹⁴₇N + ⁴₂α²⁺ –> ¹⁷₈O + ¹₁H¹⁺
¹₁H¹⁺, equal to a proton, was discovered as the constitutent part of an atom.
Discovery of the electron
J J Thompson used thermionic emission to release electrons from a heater. They were attracted to the positive plate in the shape of a cross and made an electron green glow.
It was deduced that the particle must be negatively charged because it was attracted to the positive plate. It was also found that the particle responded to electric and magnetic fields and that it had a low mass.
What was found out from the oil drop experiment?
Physicists found out from the oil drop experiment that the common factor was 1.6*10⁻¹⁹, which is the charge of the electron.
What is Einstein’s equation for energy?
E = mc² - m₀c² where m₀ is the rest mass
Discovery of the positron
Cosmic rays hitting a lead sheet were observed using a cloud chamber - an electron and an unknown particle were emitted.
The unkown particle had the same curvature of the electron, conserving momentum - it must have the same mass.
It gave the exact opposite response to the magnetic field meaning it has an equal but opposite charge to the electron.
This was the first evidence of anti-matter - the positron.
Describe pair production
Occurs when a high energy photon moves near to a nucleus
A particle and its antiparticle are produced
Photon must have equal energy to both of the particles
Describe annihilation
Occurs when a particle and its antiparticle meet
They annihilate each other and produce two gamma rays
Energy produced is equal to the energy of the particles or can be calculated with E = mc²
How do you convert from J to eV?
eV = J / 1.6*10⁻¹⁹
How do you convert from eV to J?
J = eV / 1.6*10⁻¹⁹
How many eV is equal to 1 MeV?
1 MeV = 1*10⁶ eV
Discovery of the muon
Observed to curve in the same direction of an electron but bend less than an electron
Same charge as electron but more mass - 206 times more mass
Muon denoted by μ⁻
Anti-muon denoted by ̅μ̅⁺
Discovery of the kaon
Pions were observed to appear out of nowhere
They must have been produced by the decay of an unknown particle which didn’t leave a trace in the cloud chamber
The unknown particle must therefore be neutral
Further findings:
Roughly half the mass of a proton - named kaons after this
Decayed into muons and pions, or pion pairs
Broke laws of physics
To explain this physicists decided that a new property of matter, strangeness, is needed.
What are fermions?
Matter particles
What are hadrons?
Fermions made of quarks
What are baryons?
Hadrons made of 3 quarks
Protons, neutrons
