Chapter 24 - Particle Physics Flashcards
Explain Rutherford’s Scattering Experiments
He fired alpha beams towards a thin gold metal foil in a vacuum.
Rutherford’s Scattering experiment- observations
Most of the alpha particles passed through, very few of them scattered.
1 in 10,000 were scattered for angles greater than 90 degrees.
1 in 2000 alpha particles were deflected through small angles.
Rutherford’s Scattering experiment- Conclusions
- Most of the atom was empty space with most of the mass concentrated at a small region- called the nucleus.
- The nucleus had a positive charge, because it repelled the few positive alpha particles that came near it.
What is the charge on any nucleus
+ Ze.
Where Z: atomic number of the element/
e: electronic charge.
Rutherford’s prediction of the size of the nucleus
10 ^-14
When an alpha particle approaches a nucleus, what is greater- kinetic energy or electrostatic forces of repulsion
Electrostatic forces of repulsion. Kinetic energy will be at 0, and then begin to increase as it moves away from the nucleus and accelerates.
When an alpha particle is fired towards a nucleus, what is the change in energy stores
Between electrostatic potential energy and kinetic energy.
Electrostatic potential Energy equation
Qq / 4 π ε0 d.
Electrostatic potential Energy equation
Qq / 4 π ε0 d.
What is d called?
The distance of closest approach
The calculation of KE = Qq / 4 π ε0 d. , gives what?
It gives an upper limit, as some more energetic alpha particles may get closer to the nucleus.
Charge of an alpha particle
2e
More energetic nucleus have
A radius of 10 ^-15
Radius of an atom
10^-10
Define au
1/12th the mass of a neutral carbon-12 atom.
1.661 x 10^-27 kg.
Calculation for the Radius of a nucleus
R = r0 A ^1/3
where r = 1.2 x 10^-15m
What is the radius of a proton
1.2 x 10^-15m
Why is the strong nuclear force needed?
In an atom, there are protons and neutrons.
The protons exert electrostatic forces of repulsion on the other protons. They do have the gravitational forces of attraction- but this isn’t strong enough to overcome their forces of electrostatic forces of repulsion.
So, the strong nuclear force is required to hold the entire nucleus together.
It only acts between neutron-neutron and then proton-neutrons.
It is attractive to 3fm and repulsive below about 0.5fm.
What is the density of nuclei
10^17
How can you prove that the density of a nuclei stays constant / regardless of the atomic number?
ρ = m/v .
V= volume of a sphere. where R = R = r0 A ^1/3.
and m = Au.
Then divide through, and the A’s cancel out.
All the rest of the numbers/ symbols are all constants, meaning that the density of any nucleus stays constant.
Define the antimatter
For each particle- there must be an antiparticle.
They have the same rest mass, but the opposite charge (and spin). If a particle and its corresponding antiparticle interact, then they will undergo a process called annihilate. This can mean that they destroy and release a lot of energy.
Antiparticle of an electron
Positron
What are the 4 fundamental forces
Strong nuclear
Electromagnetic
Weak nuclear
Gravitational
Effect of strong nuclear
Experienced by nucleons
Effect of electromagnetic
Experienced by static and moving particles
Effect of weak nuclear
Responsible for beta-decay
Effect of gravitational
Experienced by all objects with mass
Relative strength of strong nuclear
1
Relative strength of electromagnetic
10 ^-3
Relative strength of weak nuclear
10 ^-6
Relative strength of gravitational
10 ^ -40
Range of strong nuclear
roughly 10 ^-15.
Range of electromagnetic
infinite
Range of weak nuclear
roughly 10 ^-18
Range of gravitational
infinite
Define neutrino
A particle that’s quite similar to an electron, but has no electrical charge, and a very small mass.
Define hadrons
Particles and antiparticles that are affected by the strong nuclear force.
Define leptons
Particles and antiparticles that aren’t affected by the strong nuclear force.
Examples of hadrons
Protons, neutrons and mesons
Examples of leptons
Electrons, neutrinos and muons.
Define a quark
It is one of the building blocks of all matter, and they make up protons and neutrons.
Any particle that contains quarks is called-
A hadron
What are the 3 quarks we need to know
up, down and strange.
Symbol for an up quark
u
Symbol for a down quark
d
Symbol for a strange quark
c
Charge of an up quark
+2/3
Charge of a down quark
-1/3
Charge of a strange quark
-1/3
Define a baryon
Any hadrons made up with 3 quarks.
Define a meson
Any hadrons made up of quarks and antiquarks.
What are the 3 types of neutrinos
Electron, muon and tau.
What is responsible for beta decay
The weak nuclear force
What happens in B- decay (just description)
A neutron in an unstable nucleus decays into a proton, a electron and an electron antineutrino.
What happens in B+ decay (just description)
A proton in an unstable nucleus decays into a neutron, a positron and an electron neutrino.
What happens to the quarks in B- decay
One of the down quarks becomes an up quark.
Neutron = udd, but becomes a uud.
Total charge on both sides is -1/3e.
What happens to the quarks in B+ decay
One of the up quarks becomes a down quark.
Proton = uud, but becomes a udd.
Total charge on both sides is +2/3e.
What makes a fundamental particle
It can’t be broken into smaller pieces.
Ex: Neutrons and protons aren’t fundamental because they can be made up of quarks
