Particle Detectors Flashcards
what do school lab electron diffraction and alpha scattering experiments (by geiger and marsden) rely on in order to detect particles
- they rely on observing light given off from a fluorescent screen
- when it is hit by a particle
what does the geiger-muller tube do
- detect particles
- specifically the number of particles
what is the fundamental principle / thing that needs to occur that allows geiger-muller tubes to work
ionisation
what is the gm tube initially filled with
- an unreactive gas
- usually a noble gas like argon
what is the basic setup for a gm tube individually
- a hollow cylinder has a thin rod on the centre of its base
- one side of the cylinder is open to receive ionising radiation
- with the tube being filled with a gas
what is the name of the open side of the hollow cylinder
a mica window
what would the tube be electrically connected to in a circuit (with a cell obvs)
a geiger-muller counter
how does the tube change when it is connected into a circuit
- the thin rod acts as the anode (+ve)
- while the cylindrical shell acts as the cathode (-ve)
- making them electrodes
what else in connected to the circuit
- a resistor
- in parallel to the tube and counter
how is ionisation in this setup used in order to detect particles that are passing though the tube
- the particles passing thorough ionise atoms of the gas within the tube
- the ions and electrons produced are accelerated by an electric field formed by the electrodes in the tube
- when they come into contact with the electrode that has the opposite charge to it they discharge
- this produces a pulse of electricity which is counted by the gm counter
what is a drawback of simple particle-counting detectors like the gm counter
- they cant distinguish between different types of particles
- even though they could be receiving different types
what was the invention that essentially solved this problem
bubble chambers
what do bubble chamber diagrams look like, in professor seigbahn words
- a combination of jet-plane vapour trails
- and small bubbles that appear when you open a fizzy drink
what is the medium that bubble chamber experiments occur in
super-heated liquid hydrogen
how do the bubbles in the diagrams form
the bubbles form at any point where ions are generated within the medium
what are the ‘jet-plane vapour trails’ in reality
the path of the moving particles / ions
what kinds of lines / paths would you be seeing in a bubble chamber
- there would be straight lines mainly on the same plane (horizontal / vertical)
- some slightly curved lines that deviate off the straight path
- then some very curved lines that make several spirals
what needs to be noted about the very curved lines that make several spirals in terms of their (angular) direction
- some could be spiraling in one direction
- while the rest would be spiraling in the opposite direction
- the same is true for the slightly curved lines
what is causing the curvature and spiraling of these charged particles
the magnetic field within the bubble chamber
if the magnetic field is uniform and exerting a force on these charged particles, why are some moving in opposite directions to the others
- because theyre charges would be different
- the positively charged ions would be curving / spiraling in the opposite direction to the -ve ones
if the magnitude of the force acting on all particles is the same, due to the magnetic field being uniform, why are there some barely curved paths but also some very curved ones
- because the masses of the particles differ
- and their mass determines the radius of the curvature of their tracks
in conclusion, what do bubble chambers tell us about a number of different particles at once
their mass and charge
what else can bubble chambers show us
- interactions between particles
- as well as the creation or annihilation of particles from these interactions
how would you detect an interaction (specifically a collision) between particles in a bubble chamber diagram
- the tracks of interacting particles would have sharp changes in direction
- or begin curving in opposite directions
