Particle Interactions

Question 1

what is einstein’s most famous equation

Answer 1

E = mc^2

Question 2

what does that equation suggest

Answer 2

• matter can appear where there was previously nothing but energy
• therefore matter and energy are interchangeable in the universe

Question 3

a gamma ray photon converts into an electron and positron. how would you calculate the frequency of the gamma photon

Answer 3

• use e = mc^2 using TWICE the mass of an electron, as you basically have 2
• rearrange e = hf for f and work out f using the calculated e

Question 4

what is that specific conversion of a gamma ray photon called

Answer 4

electron-positron pair production

Question 5

what fundamental laws need to be conserved during productions like these

Answer 5

• conservation of charge
• conservation of momentum
• conservation of matter-energy

Question 6

how is charge conserved in the gamma ray photon example

Answer 6

• the gamma ray has no charge
• when it splits into an electron and positron
• the electron and positron have charges of -1 and +1
• therefore the net charge is 0
• more importantly, the net change in charge is 0

Question 7

how is charge generally conserved in these kinds of pair productions

Answer 7

• the net momentum of the pair equals the momentum of the original photon
• in both the horizontal and vertical components

Question 8

assuming the gamma ray photon was traveling directly horizontally, what could be said about the horizontal components of the electron and positiron

Answer 8

• the sum of the horizontal components of the electron-positron pair
• would equal the horizontal momentum of the photon

Question 9

what could be said about the vertical components of the electron and positron

Answer 9

• the sum of the electron-positrons vertical components equals 0
• because the photon didn’t have any momentum vertically
• in other words the vertical components of their momentum would be equal and opposite

Question 10

in this case where the electron and positron have the same mass, what could you say about their horizontal and vertical velocities

Answer 10

• in the horizontal component, they would both have the same velocity
• in the vertical component , their velocities would be equal and opposite
• both because of their identical masses, so therefore velocity would be split evenly between them`

Question 11

what do we mean by the conservation of matter-energy

Answer 11

• if we add the energy equivalent of all matter particles with the energies
• before and after the reaction
• the numbers must be equal

Question 12

what idea does nuclear fusion and fission work by

Answer 12

that energy can appear through the disappearance of mass

Question 13

how does the mass and therefore energy in a nuclear fusion or fission reaction change

Answer 13

• the sum of mass before the reaction is more than after the reaction, indicating mass has been lost
• this lost mass is converted into energy

Question 14

what is the definition of annihilation

Answer 14

• when a particle and its antimatter equivalent are both destroyed simultaneously in a conversion of energy
• which is the carried away by force carrier particles
• such as photons

Question 15

what is the value of 1eV

Answer 15

1.6x10-19

Question 16

what is 1u

Answer 16

• the mass of a proton (or hydrogen atom)

- 1u = 1.67x-27 kg

Question 17

what is the new unit(s) we can use rather than just using eV

Answer 17

• MeV / c^2

- GeV / c^2

Question 18

what is 1u of mass equivalent to in MeV / c^”

Answer 18

931.5 MeV / c^2

Question 19

how would you calculate the mass in kg of 1 MeV / c^2

Answer 19

• 1 MeV = (1x10^6) x (1.6x10-19)
• c^2 = (3x10)^2
• divide 1 MeV by c^2

Question 20

what is the definition of an electronvolt

Answer 20

the amount of energy required to move an electron through a pd of 1V

Question 21

what is the definition of pair production

Answer 21

• when a particle and its antimatter equivalent are both created simultaneously
• in a conversion from energy