Particles & Anti Particles

Question 1

How do PET scanners work?

Answer 1

• Positron emitting isotope is administered to the patient.
• Positron inside the body travels and meets electrons.
• Electrons and positrons annihilate each other, and produce two gamma photons.
• Gamma photons sensed by detector, and an image is built up.

Question 2

When does positron emission take place?

Answer 2

Positron emission takes place when a proton changes into a neutron in an unstable nucleus with too many proton .

Question 3

How are positron emitting isotopes formed?

Answer 3

• Place a stable isotope in the path of a beam of protons.

* Some of the nuclei in the substance will absorb extra protons and become unstable positron emitters.

Question 4

What did Dirac’s theory of anti particles predict?

Answer 4

Every type of particle has a corresponding anti particle.
• When meeting, will annihilate the particle, and convert their total mass into photons.
• Anti particle has the same rest mass as the particle.
• Anti particle has exactly opposite charge tot he particle ( If it has a charge ).

Question 5

What is pair production?

Answer 5

W A photon with sufficient energy passing near a nucleus or an electron can suddenly change into a particle-antiparticle pair.

Question 6

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

Answer 6

Minimum Energy of each photon produced, hf min = E0.

Question 7

What happens in pair production?

Answer 7

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

Question 8

When does annihilation occur?

Answer 8

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

Question 9

What is produced in annihilation?

Answer 9

• Two photons

Question 10

Why are two photons produced in annihilation?

Answer 10

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

Question 11

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

Answer 11

Energy of each photon = hfmin
Energy of two photons = 2hfmin
Rest energy of particle = E0
• 2hfmin = 2E0
• hfmin = E0

Question 12

What is the formula for the minimum energy of photon needed for pair production to occur?

Answer 12

Minimum energy of photon needed = hfmin = 2E0
• hfmin = Energy of one photon
• Rest energy of one particle = E0

Question 13

What happens to the mass of the particle in annihilation?

Answer 13

The mass of the particle and antiparticle is converted back into energy.