• Particles & Anti Particles

Question 1

What does every particle have?

Answer 1

Every particle has a matching anti particle.

Question 2

What are some similarities and differences between particles & anti particles

Answer 2

• Both have the same mass
• Both have the same rest energy
• Anti-particle has an opposite charge to the corresponding particle

Question 3

What is the rest energy?

Answer 3

• Rest energy of a particle is the energy equivalent of the particle’s mass.
• Measured in MeV, millions of electron volts.

Question 4

What did Dirac’s theory of anti-particles predict?

Answer 4

For every type of particle, there is a corresponding anti particle

Question 5

What are some features of anti particles?

Answer 5

• Annihilates the corresponding particle should they meet, and converts the total mass into photons.
• Has exactly the same rest mass as the particle.
• Has exactly opposite charge to the particle ( if the particle has a charge )

Question 6

What is pair production?

Answer 6

A process where a photon with sufficient energy passing near a nucleus or an electron can suddenly change into a particle-anti particle pair, which immediately separate following this interaction.

Question 7

What is an electron volt defined as?

Answer 7

One electron volt is defined as the energy transferred when an electron is moved through a potential difference of 1 volt.

Question 8

When does annihilation occur?

Answer 8

• Annihilation occurs when a particle and a corresponding anti particle meet, and their total mass is converted into radiation energy.

Question 9

What is the product of annihilation?

Answer 9

Two photons are produced.

Question 10

Why are two photons produced rather than one photon?

Answer 10

A single photon cannot ensure a total momentum of zero after the collision.

Question 11

What is the formula for the minimum energy of each photon produced?

Answer 11

• hf min = E0
E0 = rest energy of the particle.
• 2hfmin = 2E0

Question 12

What occurs in pair production?

Answer 12

A photon creates a particle and a corresponding anti, and vanishes in the process.

Question 13

What is the formula for the minimum energy that a photon requires to produce an anti particle - particle pair?

Answer 13

• A particle-anti particle, each with a rest energy E0.
• Minimum for a photon to undergo pair production, is the total rest energy of the particles produced ( each with rest energy of E0 ) =
• E min = hf min = 2E0

Question 14

What form is the energy in that is required for pair production?

Answer 14

Photons