nuclear and particle physics Flashcards
Rutherfords scattering experiment
demonstrated the existence of a nucleus. before hand we had Thompsons plum pudding model of a positive spherical atom with negative areas of charge distributed around
alpha particle scattering proof
-most particles went straight through (this proved that the atom is mostly empty space)
-sum were reflected at slight angles (this proved the nucleus is positively charged)
-very few were deflected by more that 90 degrees (which proved that the nucleus is very small and dense)
thermionic emission
a metal is heated until free electrons on its surface gain enough energy and are emitted
electron guns
use a p.d to accelerate electrons after emitted via thermionic emission. electrons accelerate towards an anode which has a small gap for electrons to pass through
LINAC
several hollow, cylindrical, metal electrodes in a line which progressively increase in length (so that particles spend the same amount of time in each tube). Adjacent electrodes are connected to opposite polarities of an alternating potential difference. this creates an electric field in the gaps between the tubes where the particles accelerate.
initially the polarity of the first electrode is opposite of the charge of the particle so it can be accelerated
Cyclotron
two semicircular electrodes called dees, with a uniform magnetic field acting perpendicular to the plane of the electrodes, and a high frequency alternating potential difference applied between electrodes. the charged particles move towards the centre of one of the electrodes and are deflected in a circular path due to the MF.
One the particles reach the edge of the electrode they begin to move across the gap between the dees, where they are accelerated by the electric field, meaning the radius of their pathway will increase. when they reach the gap again the EF changes directions so they can be accelerated.
how do bubble chambers work
when particles go through the chamber, they ionise the atoms in the vapour. this causes bubbles to gather around them. This allows you to see the path the particle took
how can particle tracks be analysed
-find the radius of the curve to find other properties using r=mV/Bq
-find the direction of curvature to see if the particles was positively or negatively charged
-analyse interaction:
if track suddenly stop, particles have collided
if tracks abruptly change direction, particles have collided
if tracks look like they have come from nothing, particle has been created from an uncharged particle like a photon which do not appear in the chamber
investigating nucleons
λ=h/p. as nucleons are so small a small wavelength is required to to investigate them. therefore particles must be of a very high energy
pair production
where a photon is converted to an equal amount of matter and anti matter. the photon must have more energy than the combined rest energy of the particles. any excess energy is converted into their kinetic energy
annihilation
where a particle and its corresponding antiparticle collide. as a result their masses are converted into energy. this energy, along with the kinetic energy of the two particles is released in the form of two photons moving in opposite directions in order to conserve momentum.
relativistic increase in particle lifetimes
when a particle is travelling at the speed of light, time dilation occurs due to special relativity. it causes time to run at different speeds depending on the motion of the observer
muon decay as an example of time dilation
they are formed in the upper atmosphere with life times of 2μ, and so should decay before reaching sea level. however, sombre found at sea level due to time dilation
hadrons
baryon
meson
baryon structure
3 quarks/anti quarks
