8.4 Creation and Annihilation of Matter

Question 1

When light acts as a particle, what are the particles called?

Answer 1

Photons

Question 2

What are the characteristics of a photon?

Answer 2

No mass, charge or any number (baryon,lepton,strangeness)

Does have energy though

Question 3

What is a photon denoted with in interactions?

Answer 3

γ (gamma)

Question 4

What happens during pair production process? photon example

Answer 4

A photon with enough energy changes into matter and antimatter.

Question 5

What is necessary to create e.g. tau and anti tau pair?

Answer 5

A photon with a great amount of energy

Question 6

Why in the diagrams do the paths of the particle and antiparticle curve?

Answer 6

As there is usually a magnetic field present in the bubble chamber in those experiments, so that they curve in opposite directions due to opposite charges.

Question 7

What is a photon?

Answer 7

A quantum of electromagnetic energy

Question 8

What is conserved in both creation and annihilation of matter?

Answer 8

charge
momentum
mass-energy

Question 9

How would we work out the minimum energy a photon must have to create an electron positron pair?

Answer 9

E = c^2 mx2

-As particles and antiparticles have the same mass

Question 10

How would we work out the frequency or wavelength of a photon?

Answer 10

e = hc/(lambda) = hf

Question 11

Can pair production only happen with photons?

Answer 11

No

Question 12

What is the opposite of pair production?

Answer 12

Annihilation

Question 13

How can we tell momentum is conserved from a diagram of bubble chamber experiment?

Answer 13

Equal but opposite curvature of particle and antiparticle

Question 14

What happens when a particle meets its antiparticle?

Answer 14

They annihilate

Question 15

What happens during annihilation? What EM is usually dissipated?

Answer 15

All the mass is converted into energy in the form of photons. Usually gamma rays

Question 16

Where are antiparticles often used in real life situations?

Answer 16

In hospitals, they are used in PET scans

Question 17

What are PET scans used for?

Answer 17

Monitoring activity in person’s brain. See which parts are active during activities.

Question 18

Why during annihilation do the photons travel in opposite directions?

Answer 18

In order to conserve momentum

Question 19

What are the characteristics of these photons?

Answer 19

They have the same energy.

Question 20

Describe and explain the process of a PET scan.

Answer 20

A human receives an oxygen isotope (injection or normal intake). During the decay in the brain positrons are emitted, these almost immediately annihilate with electrons in the brain, producing 2 gamma rays. This EM radiation is detected by scintillator(placed from both sides) and the part of the brain that the photons comes from is deduced from the difference in time to reach scintillators. A computer produces the final image.

Question 21

What would change if it was a antiproton and proton getting annihilated?

Answer 21

Due to greater mass loss, more energy would be released. Can be calculated using e = mc^2