24 - Particle Physics Flashcards
Describe the alpha particle scattering experiment.
- Alpha particles fired at gold foil
- Scattered through 180 degrees
- Detected on fluorescent sphere by microscope
What were the observations from the alpha particle experiment?
- Most particles were not scattered
- Only a very tiny amount were scattered more than 90 degrees
What can we learn about an atom from the alpha particle scattering experiment?
- Most of an atom is empty space with dense mass at centre
- Nucleus is positively charged
What is the average order of magnitude of the radius of a nucleus?
10⁻¹⁵
What is the average order of magnitude of the radius of an atom?
10⁻¹⁰
What is a nucleon?
A proton or a neutron
What is the nucleon number?
number of protons and neutrons in the nucleus
What is the top number (A) of a chemical notation?
Nucleon number
What is the bottom number (Z) of a chemical notation?
Proton number
How do we calculate the mass of an atom / nucleus?
Nucleon number x relative atomic mass (u)
What does u stand for?
Relative atomic mass.
What is the order of magnitude of density of a nucleus?
10¹⁷
What is the order of magnitude of density of an atom?
10³
Why must the strong nuclear force exist?
Because if it didn’t, the electrostatic repulsion between protons wouldn’t allow nuclei to exist.
Describe the nature of the strong nuclear force.
- Acts over a very small range
- Repulsive up to 0.5 fm
- Attractive between 0.5 and 3 fm
What is the order of magnitude of a fm?
10⁻¹⁵m
What is an antiparticle?
A particle with the same rest mass as its particle version but the opposite charge.
What happens when a particle and an antiparticle collide?
They annihilate.
How do we symbolise an anti particle?
With a bar above the symbol.
Rank the fundamental forces in order of strength.
(weakest to strongest).
Gravitational
Weak nuclear
Electromagnetic
Strong nuclear
What is a fundamental particle?
A particle with no internal structure - it cannot be further divided
What is a hadron?
A particle which is affected by the strong nuclear, weak nuclear and electromagnetic forces.
Made of quarks.
Give three examples of hadrons.
Protons
Neutrons
Mesons
What is a lepton?
A particle not affected by the strong nuclear force but affected by the weak nuclear and electromagnetic forces.
Give three examples of leptons.
Electrons
Neutrinos
Muons
What are hadrons made of?
Quarks.
What is the name of a hadron made of 3 quarks?
Baryons
What is the name of hadrons made of 2 quarks?
Mesons
Describe beta minus decay.
Neutron decays into a proton, an electron and an antineutrino
Describe beta plus decay.
Proton decays into a neutron, a positron and a neutrino
What is always conserved in beta minus decay?
Nucleon number and charge
Describe beta minus decay in terms of quarks.
A down quark decays into an up quark.
Describe beta plus decay in terms of quarks.
An up quark decays into a down quark.
Describe the quark makeup of a proton.
UUD
Describe the quark makeup of a neutron.
UDD
