Nuclear and Particle Physics

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In nuclear equations what do A and Z represent?
A - Nucleon (mass) number is the total number of protons and neutrons in the nucleus. Z - proton number defines the physical and chemical properties
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What is the Atomic Mass Unit
The unified atomic mass unit as defined as 1/12th the mass of an atom of Carbon-12
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Describe Rutherford's Gold Foil experiment
Alpha particles where fired at a thin piece of gold foil, a recpetor on a curved track was one the other side of the foil to detect the alpha particles
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What did he observe?
Most particles pass straight through the foil, very were deflected through angles greater than 90 degrees, particles were deflected at all angles.
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What conclusions were drawn from the experiment to form Rutherford's model of the atom?
The majority of the mass of an atom exists in the nucleus, the nucleus is very small complared to the size of the atom, the nucleus is charged, the atom is mostly empty space
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What is fine structure?
The structral makeup of subatomic particles
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How was the fine structure of protons and neutrons studied?
High energy electrons with de Broglie wavelengths small enough to diffract through the nucleons were fired at them to demonstrate deep inelastic scattering
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What are the two groups of elementary particles?
Quarks and Leptons
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Name all the quarks
Up, Down, Charm, Strange, Top, Bottom and their anti-particles
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Why does a particle with one strange quark have a strangeness value of minus one?
Because the anti-strange quark was discovered first
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Name all the leptons
Electron, Muon, Tauon, Neutrinos of each and their anti-particles
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What are the three groups of composite particles?
Hadrons, Baryons and Mesons
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Define Hadrons
All types of particles made up of quarks
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Define Baryons and give two common examples with their quark makeup
Hadrons made up of three quarks - Proton (uud) and Neutron (udd)
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Define Mesons and give two common examples
Hadrons made up of a quark-antiquark pair - Pions and Kaons
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What is an Anti-particle?
A particle exactly the same as a regular elementary particle but with opposite charge
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What is always conserved in particle interactions?
Total charge, momentum, mass-energy, baryon number and lepton number
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What is an electronvolt?
Small unit of energy equivalent to the KE gained by an electron accelerated across a 1 volt potential difference
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Why is the electronvolt useful?
Used very small energies
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What is eV/c^2 and why is it useful?
A convenient mass unit used in relativistic and nuclear equations - obtained by dividing the energy in electronvolts by the speed of light squared
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How does an Electron Gun (cathode ray tube) work?
Electrons are given off by thermionic emission at a hot metal cathode then accelerated by a large potential difference towards the anode which has a gap in it allowing a stream of fast moving electrons to pass through
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How is the kinetic energy of electrons exiting the gun calculated?
KE = qV (charge of each particle x potential difference)
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Why does a CRT produce limited energy particles?
Electrons have such tiny mass
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What does LINAC mean
Linear Accelerator
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How does a Drift Tube Accelerator work?
Consecutive drift tubes of increasing lengths are charged by high frequency alternating current to create an electric field in between the tubes through which a particle is accelerated
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Where do particles experience a force?
Between the tubes
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Why must polarity of the tubes switch?
To make the particle always acclerate towards the next tube
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Why do the tube lengths increase?
As the particles velocity increases so must tube length so that the particle spends the same amount of time in each tube
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Why are tubes near the end of the accelerator equal length?
As particles approach the speed of light any extra energy is used to increase mass, not energy (relativistic effects act)
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What are the limiting factors of a LINAC?
Physical size (length) and the additional cost of each section restricts the size of the accelerator and therefore achievable energies
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What is a cyclotron, what does it consist of?
Spiral shaped particle accelerator consisting of a source of charged particles at the centre, charged 'Dees' with high frequency AC creating an electric field in the gap in between, constant perpendicular magnetic field to cause particles to cuvre
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How are particles accelerated?
Electric field in the gap between Dees provides a resultant force to accelerate particles across the gap, increasing KE
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Why must the current alternate?
TO reverse the field so particles are always accelerate in the same direction across the field
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Why do the particles spiral outwards?
r = p/BQ as momentum increases so does path radius for a constant magnetic field
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What limits the particle energies that can be produced by a cyclotron?
When particles approach the speed of light mass increases instead of velocity, this means the paricles become out of phase with the AC supply
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State similarities between a LINAC and cyclotron
Both use electric fields to accelerate charge particles, Work is done on particles only in the gaps (between the tubes and Dees)
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State some differences
LINAC accelerates particles in a straight line, Cyclotron uses magnetic field to curve the path into a spiral. Increasing velocity requires increasing tube length in a LINAC but increasing radius in a cyclotron
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Why are high energy particles useful for scientific studies?
Relativistic effects can only be shown with very high energies and high energies can overcome repulsive particles
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What is a synchrotron?
Circular particle accelerator similar to a cyclotron
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Why does a synchrotron have constant radius?
Frequency of accelerating electric field and strength of magnetic field to keep particles of increasing mass in a circular path
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What are the two types of target for high energy particles?
Colliding beams and fixed targets
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Give advantages of colliding beams
Ad: Larger mass particles produced, zero initial and final total momentum, product particles don't need KE so all energy is available to produce mass by relativistic effects
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Give disadvantages of colliding beams
Low collision rate as colliding individual beams is difficult
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Give advantages of using a fixed target
High number of collisions
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Give disadvantages of using a fixed target
Smaller mass particles produced, there is linear momentum before and after collision so products must have KE therefore not all of the collision energy can produce mass
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How do most particle detectors work?
Particles interact with matter causing ionisation,
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Give two basic examples of particle detectors
Cloud chamber and Bubble chamber
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How does a cloud chamber work?
Air supersaturated with alcohol, particles cause ionisation of the air, ions act as condensation sites and vapour trail produced shows the path of the particle
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How does a bubble chamber work?
Very hot, highly pressurised liquid hydrogen is ionised by charged particles creating bubbles of hydrogen gas. Tracks of bubbles give evidence of the particle's path
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Describe and explain the track produced by an alpha particle
Short, fat track produced due to high ionising power and large mass
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How are perpendicular magnetic fields used in particle detectors?
Charged particles curve in the magnetic field, the shape and direction of curve can give information about the charge and mass of the particles
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How are electric fields used in particle detectors?
The way in which a particle is accelerate or deflected through an E-field gives information about mass and charge
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Why do photons and neutrons produce no track?
They have no charge so do not ionise the target
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Why might unstable particles have a longer than expected observed mean lifetime?
Time dilation due to relativistic effects as speed approaches the speed of light
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Other cards in this set

Card 2

Front

What is the Atomic Mass Unit

Back

The unified atomic mass unit as defined as 1/12th the mass of an atom of Carbon-12

Card 3

Front

Describe Rutherford's Gold Foil experiment

Back

Preview of the front of card 3

Card 4

Front

What did he observe?

Back

Preview of the front of card 4

Card 5

Front

What conclusions were drawn from the experiment to form Rutherford's model of the atom?

Back

Preview of the front of card 5
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