Chapter 24 - Particle Physics Flashcards
Alpha scattering experiment
- A narrow beam of photons (with the same Ek were fired at a thin sheet of gold foil)
- The alpha particles were scattered and detected on a zinc sulfide screen mounted on the end of a microscope
- Each alpha particle created a tiny speck of light so they counted the amount of particles scattered through different angles per minute
Alpha scattering experiment observations
If the plum pudding model were correct all of the alpha particles would have passed straight through
- Around 1 in every 2000 particles were scattered
- Around 1 in every 10000 was deflected at an angle >90
Alpha scattering experiment findings
Most of the atom was empty space (most passed through)
The atom had a concentration of mass (some deflected at angles >90)
The atom had a concentration of positive charge (some deflected)
The nucleus must have a size of around 10^-14 m
Charge of a nucleus formula
Q = +/- Ze
where Z is the atomic number
Why were alpha particles scattered
Because of the electrostatic repulsion with the electric field of the nucleus, they wouldn’t actually hit the nucleus
Kinetic energy formula from the alpha scattering experiment
Ek = Qq/4πε0d
where Q, q are the two charges and d the distance to the nucleus
Size of a nucleus
Around 10^-15 m
Size of an atom
Around 10^-10m
Isotopes
Nuclei of the same element that have the same amount of protons but a different amount of neutrons
Atomic labelling system
A
X
Z
where A is the nucleon number (protons + neutrons) and P is the proton number
Atomic mass unit (u) definition
One twelfth of the mass of a neutral carbon-12 atom
Atomic mass unit (u)
(1.661 x 10^-27)kg
Protons and neutrons can be treated as having a mass of 1 u and electrons 0
Radius of a nucleus formula
R = r0 A^1/3
where r0 is the minimum radius of a nucleus and A the nucleon number
r0
around 1.2 x 10^-15
Finding density of a nucleus
Mass is nucleon number x u
Volume is 4/3 π r^3
ρ = m/V
Antimatter
Every particle has a corresponding antiparticle that will completely annihilate each other if they meet, converting the two masses to photons
Have the same mass and opposite charge of the particle
Generally shown by the particle’s symbol with a bar above
Strong nuclear force
Experienced by nucleons, range around 10^-15m
Repulsive over a short distance, attractive a larger one
Electromagnetic force
Experienced by static and moving charged particles, relative strength 10^-3 compared to strong nuclear, infinite range
Weak nuclear force
Responsible for beta decay, relative strength 10^-6 compared to strong nuclear, range around 10^-18m
Gravitational force
Experienced by all particles with mass, relative strength 10^-40 compared with strong nuclear, infinite range
Fundamental particles
Have no internal structure and can’t be broken down further
Fundamental quarks
up. down, top, bottom, charm, strange
Fundamental non-quark particles
electron, muon, tau and their anti-particles
Hadrons
Particles and anti-particles that are affected by the strong nuclear force.
Can also decay by the weak nuclear force and are affected by the EM force if charged
e.g. protons, neutrons, mesons
Leptons
Particles and antiparticles that are not affected by the strong nuclear force. Experience the EM force if charged
e.g. electron, tau, muon
Up quark
u, charge +2/3 e
Down quark
d, charge -1/3 e
Strange quark
s, charge -1/3 e
Proton quarks
uud
Neutron quarks
udd
Baryons
Hadrons made up of three quarks
Mesons
Hadrons made of a quark and an anti-quark
Neutrino
No charge, mass less than a millionths that of an electron
Up to 100 million per cubic metre
Electron, tau, muon neutrinos and anti-neutrinos
Symbol nu and the other symbol in subscript
Beta minus decay
Neutron -> proton + electron + electron anti-neutrino
1 1 0 -
0 n –> 1 p + -1 e + νe
Beta plus decay
Proton -> neutron + positron + electron neutrino
1 1 0
1 p –> 0 n + +1 e + νe
Beta minus quarks
0 -
d –> u + -1 e + νe
Beta plus quarks
0 -
u –> d + +1 e + νe
What is conserved in beta decay?
Charge, nucleon number, proton number
Strong nuclear force attractive and repulsive distances
< 3fm - attractive
< 0.5fm - repulsive
