Nuclear and Particle Flashcards
What is nucleon number?
The sum of the number of protons and neutrons in the nucleus
What is atomic number?
The total number of protons in the nucleus
Outline Rutherford’s alpha scattering experiment.
High speed alpha particles were fired at a very thin sheet of gold foil. The deflections of the particles were measured and conclusions were drawn
What was observed in the Alpha scattering experiment?
- Most of the alpha particles passed straight through the gold aomts
- Some of them were deflected slightly (less than 90)
- A few of them were deflected backwards (greater than 90)
What is thermionic emission?
The release of electrons due to heating
Explain why electrons are released from a heated filament.
As the filament heats up, free electrons inside the metal gain kinetic energy. When the surface electrons gain sufficient energy, they are released from the surface
What happens to a beam of electrons if it is passed through a potential difference?
The beam of electrons will be accelerated since work is done by the potential difference
How do you calculate the energy transferred to an electron, when it is accelerated across a potential difference?
Energy = Charge x Potential Difference
What happens when a beam of electrons is directed into a magnetic field?
The electron beam will be deflected, since magnetic fields apply forces on moving charges
What is the magnitude of the force experienced by a moving electgron in a magnetic field?
Force = Magnetic Flux Density x Charge x Velocity
F = Bqv
If electrons are moving perpendicular to the field lines, which direction will the magnetic force act?
The force will act perpendicular to both the electron and field directions
Describe the shape of the path of a beam of electrons passing through a magnetic field.
The beam will produce a circular path since the magnetic force always acts perpendicular to the electrons’ motion. This means it acts as a centripetal force and produces a circular path
What is a cyclotron?
A cyclotron is a particle accelerator that uses magnetic fields to accelerate particles in circular paths. Thisi allows higher speeds to be reached, without the limitation of the accelerator’s length
Describe the basic composition of a cyclotron.
Cyclotron consists of two D-shaped paths which are separated by a small gap. An alternating potential difference is applied across the gap.
How does a cycltron work
An electron beam is passed into the cyclotron, where it is deflected into a circular path by a perpendicular magnetic field. When the beam reaches the gap, it is acclereated by a potential difference. This increases the speed of the beam, causing the radius of the path to increase. This process repeats every half cycle
State the equation used to calculate the circular radius of an electron beam deflected in a magnetic field.
Radius = mv/ Bq
What two equations must you combine to derive the radius equation?
- Centripetal force = mv^2/r
- Magnetic force = BQv
centripetal = magnetic force
State the mass energy equation.
E = mc^2
What is 1 MeV in joules?
1.6 x10^-13 J
In the quark lepton model, what are the four main categories of particles?
- Baryons
- Mesons
- Leptons
- Photons
State the composition of a baryon.
Baryons are made up of three quarks
Describe the composition of a meson.
Mesons are made of a quark-antiquark pair
Which categories of particles are classed as fundamental particles?
Leptons
Give two examples of leptons.
Electron, Neutrinos, Muon
What category of particles do pions belong in?
Mesons
Give two examples of baryons.
Protons, neutrons
What did the symmetry of the quark-lepton model predict the existence of?
The top quark
What is an antiparticle?
An antiparticle is one that has the same mass but opposite charge and conservation numbers to its corresponding particle
What is the antiparticle of a proton?
An antiproton
What is the antiparticle of an electron?
A positron
Name four things that are always conserved in a particle interaction?
- Baryon Number
- Lepton Number
- Charge
- Mass / Energy
Describe the conservation of lepton number.
The lepton number for each specific type of lepton must be the same before and after an interaction
Describe how Chadwick found the existence of neutrons.
He fired alpha particles at Li atoms and noticed radiation was released but was not charged. He put a sheet of parafin in front and protons shoot out so the ‘thing’ needed to be heavy enough to cause protons to move, came up with the neutron
He used the conservation of momentum and energy to say they are uncharged and approximately the same mass of a proton
What are the conclusions based on particles scattering?
- 0-10
- 10 -90
- 90+
- 0-10. Most particles pass straight through with little deviation, therefore most of the atom is empty space
- 10-90 Some particles deflected a large angle tells us there is a concentration of charge in one place
-90+ few particles repelled back, so most of the mass and large concentration of charge in a tiny. central nucleus
What was the model of the atom before the nuclear model?
The plum pudding model; a ball of a positive body with electrons scattered throughout
As you progress through the periodic table, more neutrons are required for the atom to be stable, why?
More neutrons are generally needed to help bind the nucleus together as they exert a strong nuclear force on other electrons. They also act as a space buffer between mutually repelling protons. So as you go through the periodic table, atoms have more protons so more neutrons are required to buffer them
What is the electronvolt?
The kinetic energy carried by an electron after it has been accelerated through a pd of 1v
1eV = 1.6 x10^-19 J
What is a cathode ray?
A beam of electrons - you can use thermionic emission to produce electrons, apply an electric field to accelerate them to produce a fast-moving beam of electrons (cathode ray
Give the de broglie wavelength equation?
lambda = h/mv
de broglie wavelength = planck’s constant / wavelength
Why do the tubes in a linear acclerator have to get longer?
As particles leave one tube into the next, their speed increases, in order to keep accelerating the particles, the tubes need to be made longer so the particle spends the same time in each one
How does a LINAC work?
It is a long, straight tube containing a series of electrodes. The charge on each electrode alternates along the tubes which allows the electron to move in a straight line as the electrodes are connected to opposite ends of an alternating pd so the electrodes are always switching firection allowing particles to accelerate
What is found to happen as particles are accelerated close to the speed of light?
As particles were accelerated to what should have pushed them beyond the speed of light, their Ke and momentum continued to increase but their speed did not therefore the mass of the particle must increase
How can you calculate the frequency of polarity switches in a cyclotron?
T = 2πr/v and r =mv/BQ
f= 1/T therefore
f= BQ/2πm
