Particle & Nuclear Physics Flashcards
How did Rutherfords alpha scattering experiment work?
- A narrow beam of alpha particles (all of the same kinetic energy) from a radioactive source was targeted at a thin piece of gold, only a few atoms thick
- The alpha particles were scattered by the foil and detected on a zinc sulfide screen mounted in front of a microscope
- Each alpha particles hitting the fluorescent screen produced a tiny speck of light
- The microscope was moved around in order to count the number of alpha particles scattered through different angles per minute, for 0 to almost 180 degrees
What were the observations of Rutherfords alpha scattering experiment?
- Most of the alpha particles passed straight through the thin gold foil with very little scattering
- Very few of the alpha particles (about 1 in 10,000) were defelected though angles of more than 10 degrees
What were the conclusions for Rutherfords alpha scattering experiment?
- Most of the atom was empty space, with most of the mass concentrated in a small region
- The nucleus has a positive charge because it repelled the few positive alpha charges that came near it
What is the charge of a proton?
1.6 x 10^-19 C
What is the charge of an electron?
- 1.6 x 10^-19 C
What is the charge of a neutron
0 C
What is the mass of a proton?
1.67 x 10^-27 kg
What is the mass of a neutron?
1.67 x 10^-27 kg
What is the mass of an electron?
9.11 x 10^-31 kg
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of a neutron?
-1
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/2000
What is the diameter of an atom?
1 x 10^-10 m
What is the diameter of a nucleus?
1 x 10^-15 m
What is the closest approach method?
- In the rutherford scattering experiment, alpha particles are fired at a thin gold foil
- Some of the alpha particles are found to come straight back from the gold foil
- This indicates that there is electrostatic repulsion between the alpha particles and the gold nucleus : KE = eV = 1/2 mv^2
- At the point of closest approach, r, the repulsive force reduces the speed of the alpha particles to 0 momentarily
- At this point : initial KE of alpha particle = electric potential energy
What is the closest approach equation?
KE = Qq / 4 pi ε r
What is the nucleon number?
Total number of protons & neutrons in the nucleus
What is the proton number?
Total number of protons in the nucleus
What is the notation showing nucleon and proton number of an element?
What is an isotope?
An atom (of the same element) that has an equal number of protons but a different number of neutrons. The proton number is the same but the nucleon number is different?
What can the nucleon number also be called?
Mass number
What type of properties do neutrons not affect?
The chemical properties eg. charge
What properties do isotopes have different to the normal atoms?
Physical properties eg. mass
Why do isotopes tend to be more unstable?
Due to the imbalance of protons and neutrons
What 3 forces are there in the nucleus?
- Electrostatic forces (repulsion)
- Gravitational forces (attraction)
- The strong nuclear force
Why are there electrostatic forces in the nucleus?
Due to the charge of the protons
Why are there gravitational forces in the nucleus?
Because of the masses of the nucleons
What is the strong nuclear force?
The force that holds the nucleus together - it acts between all nucleons. It is one of the 4 fundamental forces
What is the range of the strong nuclear force?
Very short range, effective over just a few fentometres
What is the nature of the strong nuclear force (inc. ranges) ?
- Repulsive below 0.5 fm
- Attractive up to 3fm
- 0 after 3fm
What is the equation for radius of a nuclei?
R = radius of nuclei
r0 = constant
A = nucleon number
What is the value of constant r0?
1.2 x 10^-15 m
How do you show the density of a nucleus is constant and independent of the radius?
What is the universe made up of?
Matter particles
What is antimatter?
Matter counter particles - they are identical to their matter counterparts but have opposite charge
What is the antiparticle of the electron?
Positron
What is the antiparticle of the proton?
Anti-proton
What is a neutral particles anti particle?
Itself - because it has a neutral charge anyways
What do matter and anti-matter particles have identical to one another?
Their mass and rest-mass energy
What is a hadron?
Particles and anti-particles that are affected by the strong nuclear force
What are some examples of hadrons?
Protons
Neutrons
Mesons
What force are hadrons subject to when charged?
Electromagnetic charge
What force does decay occur by for hadrons?
The weak nuclear force
What is a lepton?
Particles and anti-particles that are not affected by the strong nuclear force
What forces are leptons subject to when charged?
Electromagnetic force
What other force are leptons subject to?
The weak nuclear force
What are some examples of leptons?
- Electrons
- Neutrinos
- Muons
What are neutrinos?
The most abundant leptons in the universe - they have no charge and negligible mass
What are the 3 flavours of neutrino?
What are the other 3 leptons (other than the neutrinos)?
- Electron
- Muon
- Tau
What are the 2 types of hadrons?
Baryon and meson
What is baryon?
A hadron from 3 quarks
What is a meson?
A hadron made from a quark and anti-quark pair
What is an anti-baryon?
An anti-hadron made from 3 anti-quarks
What is an anti-meson?
An anti hadron made from a quark and anti-quark pair
In refernce to charge, what do all baryons and mesons have?
Integer charges, eg +1e, -2e
This means quarks in a baryon are either all quarks or all anti-quarks
Why are protons and neutrons not fundamental particles?
Because they are each made up of 3 quarks