Module 6 Nuclear and Particle Physics Flashcards
What is a typical diameter for an atom?
Apx 10^-10m
What is a typical diameter for a nucleus?
10^-15 or 10^-14
Symbol for proton number?
Z
Symbol for nucleon number?
A
What is a nucleon?
A particle found in the nucleus of an atom, which includes protons and neutrons
Symbol for neutron number?
N
What is an isotope?
Same proton number different nucleon number
What are the assumptions made for nuclear reactions?
Conservation of the usual stuff (mass, momentum, energy etc)
Nucleon number is conserved
Charge is conserved (bottom number)
What is an alpha particle?
A helium nucleus
What is a positron?
Same as electron but with a positive charge
Describe the apparatus used in Rutherford’s experiment.
A sample of radioactive material which emits alpha particles in a lead block with a narrow hole to produce a beam of alpha particles in a vacuum.
Why is a vacuum necessary in Rutherford’s experiment?
To prevent air molecules from interfering with the path of the alpha particles.
Why does the gold foil need to be rolled thin?
Allows alpha particles to pass through and be detected as they can be absorbed by paper.
Describe the results of the Rutherford experiment.
Most alpha particles travel through the foil undetected, implying the atom is mostly empty space.
Some alpha particles are deflected by small angles, implying the nucleus is positively charged.
Very few particles are detected traveling back from the foil, meaning the nucleus has most of the atom’s mass and is very small compared to the rest of the atom.
What is the simple conclusion of Rutherford’s experiment?
Atom contains a nucleus (centre) which is very small, positively charged and contains most of the atom’s mass.
How can the zinc sulphide screen be adjusted to gain more accurate results?
Move it closer to the gold foil.
What can be used to calculate the closest approach of an alpha particle to a nucleus?
Coulombs Law
Describe how the closest approach can be calculated.
At closest approach all KE is converted to electrostatic PE. Qq are the respective charges of the nucleus and the alpha particle.
What is the evidence to show that there must be a third force within a nucleus to keep itself intact?
Calculate force due to gravity and Coulomb force separately. Gravity is attractive whereas electrostatic forces are repulsive. Ratio of forceE/forceG is massive meaning gravitational force is negligible.
What does strong nuclear force act on?
Neighbouring protons and neutrons equally
What is the prefix femto?
10^-15
Describe how strong nuclear force varies.
Separation of r>3fm force is negligible.
Separation of 0.5 to 3fm force is very high magnitude and attractive.
Separation of r<0.5fm force is of very high magnitude and repulsive.
Explain why neutrons increase nuclear stability.
Strong nuclear force has a short range, only affecting adjacent nucleons and is attractive.
Coulomb force has an infinite range and acts between all protons inside the nucleus and is repulsive.
The more neutrons there are, the more the overall strong nuclear force of attraction is increased without contributing to the Coulomb force.
Describe how you would determine PD required for an alpha particle to be accelerated so that it fuses with a nucleus.
Put Qq as charge of nucleus and alpha particle respectively into Coulombs equation for energy (V).
Describe a simple experiment to show that the radius of a nucleus is directly proportional to the cube root of the nucleon number.
High energy electrons are accelerated through a PD to a de Broglie wavelength of approx 1fm, fired at samples of nuclei which are diffracted around a nucleus and the pattern is used to find a value of R. Repeated for many different nuclei of known sizes.
What is an approximate value for r_0, the radius of one nucleon?
. 1.25fm
When plotting a graph of R=r_0A^1/3 in log form, how do you find r_0?
Y intercept is log r_0.
How to show that nuclear density is independent of size of nucleus?
Take mass as A x 1.7x10^-27.
Substitute r_0A^1/3 for R in equation for volume (is cubed). A cancels out.
What are the two main groups of particles?
Hadrons and Leptons
What does fundamental mean?
Is not comprised of smaller particles, cannot be split up further.
What does the electron family consist of?
Electrons, Positrons, Neutrinos, Anti-neutrinos
What are the two subgroups of hadrons?
Baryons and Mesons
What is the composition of a baryon?
Three quarks
What is the composition of a meson?
Quark antiquark pair
Give an example of a meson.
A pion
What is different for antiparticles?
Opposite charge and opposite baryon/lepton number.
What types of forces do leptons interact with?
Weak nuclear force, Gravity, Electromagnetic
What force do leptons not experience?
Strong nuclear forces
Give an example of a lepton.
Electron, Neutrino
What is the lepton number for a positron?
-1
Mass of a neutrino?
Approx 0
What are hadrons comprised of?
Quarks
What is the baryon number of a quark?
1/3
What is the baryon number of a meson?
0
What is the notation for an antiparticle?
Put a bar over the symbol (eg. n with a bar on is an antineutron)
Which quarks are neutrons made of?
udd
Which quarks are protons made of?
uud
What does beta minus decay emit?
A fast moving electron and an antineutrino
When does beta minus decay occur?
In an unstable nucleus with too many neutrons
Give the equation for the quark model of beta minus decay.
udd ⇒ uud + e- + v(bar)
In words
neutron decays in to proton + electron + anitneutrino
How to remember between beta minus and plus decay?
Minus produces a negatively charged electron.
When does beta plus decay occur?
When an unstable nucleus has too many protons.
What happens during beta plus decay?
A proton is converted into a neutron, a positron, and a neutrino.
What is annihilation?
When a particle meets its antiparticle in a head-on collision. Both are destroyed and mass is converted to photon energy using the equation according to E=mc^2.
Why do a minimum of two photons need to be produced during annihilation?
To conserve total momentum.
What happens to initial KE of particles during annihilation?
Is added to final total photon energy.
Why must photons be emitted on the same straight line during annihilation?
So their momentums cancel out (so momentum is conserved).
How would you find the frequency of radiation needed to produce a quark?
Calculate the energy needed using E=mc^2. Calculate f using E=hf.
What happens during pair production?
A particle and its anti-particle are created directly from energy.
When can pair production take place?
Collisions between particles in an accelerator or directly from photons.
