Particle Detectors

Question 1

what do school lab electron diffraction and alpha scattering experiments (by geiger and marsden) rely on in order to detect particles

Answer 1

• they rely on observing light given off from a fluorescent screen
• when it is hit by a particle

Question 2

what does the geiger-muller tube do

Answer 2

• detect particles

- specifically the number of particles

Question 3

what is the fundamental principle / thing that needs to occur that allows geiger-muller tubes to work

Answer 3

ionisation

Question 4

what is the gm tube initially filled with

Answer 4

• an unreactive gas

- usually a noble gas like argon

Question 5

what is the basic setup for a gm tube individually

Answer 5

• 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

Question 6

what is the name of the open side of the hollow cylinder

Answer 6

a mica window

Question 7

what would the tube be electrically connected to in a circuit (with a cell obvs)

Answer 7

a geiger-muller counter

Question 8

how does the tube change when it is connected into a circuit

Answer 8

• the thin rod acts as the anode (+ve)
• while the cylindrical shell acts as the cathode (-ve)
• making them electrodes

Question 9

what else in connected to the circuit

Answer 9

• a resistor

- in parallel to the tube and counter

Question 10

how is ionisation in this setup used in order to detect particles that are passing though the tube

Answer 10

• 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

Question 11

what is a drawback of simple particle-counting detectors like the gm counter

Answer 11

• they cant distinguish between different types of particles

- even though they could be receiving different types

Question 12

what was the invention that essentially solved this problem

Answer 12

bubble chambers

Question 13

what do bubble chamber diagrams look like, in professor seigbahn words

Answer 13

• a combination of jet-plane vapour trails

- and small bubbles that appear when you open a fizzy drink

Question 14

what is the medium that bubble chamber experiments occur in

Answer 14

super-heated liquid hydrogen

Question 15

how do the bubbles in the diagrams form

Answer 15

the bubbles form at any point where ions are generated within the medium

Question 16

what are the ‘jet-plane vapour trails’ in reality

Answer 16

the path of the moving particles / ions

Question 17

what kinds of lines / paths would you be seeing in a bubble chamber

Answer 17

• 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

Question 18

what needs to be noted about the very curved lines that make several spirals in terms of their (angular) direction

Answer 18

• 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

Question 19

what is causing the curvature and spiraling of these charged particles

Answer 19

the magnetic field within the bubble chamber

Question 20

if the magnetic field is uniform and exerting a force on these charged particles, why are some moving in opposite directions to the others

Answer 20

• because theyre charges would be different

- the positively charged ions would be curving / spiraling in the opposite direction to the -ve ones

Question 21

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

Answer 21

• because the masses of the particles differ

- and their mass determines the radius of the curvature of their tracks

Question 22

in conclusion, what do bubble chambers tell us about a number of different particles at once

Answer 22

their mass and charge

Question 23

what else can bubble chambers show us

Answer 23

• interactions between particles

- as well as the creation or annihilation of particles from these interactions

Question 24

how would you detect an interaction (specifically a collision) between particles in a bubble chamber diagram

Answer 24

• the tracks of interacting particles would have sharp changes in direction
• or begin curving in opposite directions

Question 25

how would you know if interacting particles had annihilated each other from a bubble chamber diagram

Answer 25

the tracks of the interacting particles would end abruptly

Question 26

what would tracks appearing from seemingly out of nowhere be indicating

Answer 26

• the creation of a particle

- specifically, from an uncharged particle that didnt show up

Question 27

why do uncharged particles not show up on bubble chambers

Answer 27

because they cant be affected by the magnetic field

Question 28

what is a bubble chamber

Answer 28

• a particle detection system
• in which the particles trigger bubbles to be created in a super-heated liquid
• typically hydrogen