Nuclear and particle physics Flashcards
How do LINAC’s work?
There are cylindrical tubes called ‘drift tubes’. These tubes increase in length as you move along the cyclotron.
Adjacent electrodes are connected alternately to either side of an alternating p.d. The tube changes polarity at fixed time intervals.
There is no electric field in the tubes, therefore the electrons only accelerate in the gaps of the tube.
As an electron enters a tube, the tube it enters becomes negative while the next tube changes to positive, this means the electron is repelled by the tube it is in and attracted to the adjacent tube.
This process continues, but the tubes increase in length each time, as the tubes increase, the electron accelerates in the gaps, this means that the time taken to go through each tube is constant and the same is for the time period.
At the end of the LINAC the tubes become the same L due to particle reaching maximum speed.
How do cyclotrons work?
Cyclotrons are made up of two semi-circular electrodes referred to as ‘dees’.
There is a uniform magnetic field acting perpendicular to the dees. This causes the electron to move in a circular path but not to accelerate.
Between the two dees, there is a high frequency and alternating voltage being applied, this is where the electron accelerates.
As the electron approaches the gap the alternating field changes direction.
As the electrons speed increases so does their radius meaning a greater distance needed to travel within the dee. However the time to travel around the dee stays constant due to the acceleration. This is shown by r=mv/BQ r is proportional to v as all the others are constant, as r increases so does v.
What is thermionic emission?
This is when the metal is heated, transferring energy to the free electrons, once the free electrons have enough energy they will be emitted.
How do electron guns work?
Electron guns use a potential difference to accelerate electrons. The electrons are emitted from the cathode (-ve), where they have been heated to cause thermionic emission, it then is attracted to the anode (+ve) which has a hole where many electrons will pass through.
E=QV
e(the charge of the electron)= Q. so E=eV. This energy becomes the KE of the electron. SO eV=1/2mv^2.
Bubble chambers
The tank is filled with super heated liquid hydrogen.
Bubble’s are formed around any charged particle, this creates tracks as the particle moves.
The tank is placed in a magnetic field meaning the particles move in a circular path.
You can:
Find characteristics about the particle by finding the radius and using r=mv/BQ.
Look at the direction it curves and using Fleming’s left hand rule deduce its charge.
Sudden halts or direction changes means it has collided.
If the particle suddenly appears it means it has been created from an uncharged particle (photon).
What is pair production?
This is where a energy can be converted into equal amounts of matter and antimatter (e.g electron and positron). For example, fire two protons at each other, the high energy at the point of impact can form more particles.
This can only occur when the energy of the photon is greater than both the energies of the matter and antimatter.
Any excess energy will be converted into KE for the particles.
This phenomena can be explained by e=mc^2, which shows that energy and mass are interchangeable.
What is annihilation?
This is where a particle and its antiparticle collide, as a result their masses are converted into energy. This along with the KE of both particles is released as two photons moving in opposite directions to conserve momentum.
Why are high energies required when investigating the structure of nucleons?
When investigating an object waves similar to that object must be used.
To find wavelength you must use wavelength=h/p where h is a known constant. p=mv. Therefore the lower the wavelength the greater the energy required.
Nucleons have a very small wavelength of around 1.6x10^-15. This means tremendous amounts of energy are required to investigate them.
What are all the quarks?
Top,Bottom,Up,Down,Charm, Srange
What happens when an antiparticle meet their corresponding particle?
The antiparticles are annihilated
What type of particle provides strong force?
Baryons (protons and neutrons).
Do baryons only provide strong force?
Protons provide electrostatic force (which has infinite range), while neutrons only provide strong force.
What is roughly the range of strong force?
3-4 fm (x10^-15)
Why do many elements have many more neutrons that smaller elements?
This is because neutrons have a strong force but not an electrostatic force making the element more stable.
What is strong force?
Strong force is a force that is only applicable on the particle level. This is a force that attracts two baryons when they are too for from each other but repel when they are too close, the strong force applies no force when two protons are at the equilibrium position which is about 1x10^-15 m.
