1.4 Particles and antiparticles

Question 1

What is the universe made up of?

Answer 1

» Antimatter and matter

Question 2

What happens when antimatter and matter meet?

Answer 2

» When antimatter and matter meet they destroy one another and radiation is released

Question 3

What does PET scanner stand for?

Answer 3

» PET Positron emitting tomography - uses this effect for a scanner

Question 4

How does a PET scanner work?

Answer 4

» A positron-emitting isotope is administered to the patient and some of it reaches the brain via the blood system

» Each position emitted travels no further than a few millimetres before it meets an electron and they annihilate each other

» Consequently 2 gamma photons is produced and are sensed by detectors linked to a computer - gradually an image is built up from the detector of where the nuclei are inside the brain

Question 5

When does positron emission take place?

Answer 5

» Takes place when a proton changes into a neutron

Question 6

What is the positron the antiparticle of?

Answer 6

» An electron

Question 7

What is the equation of when a proton changes into a neutron?

Answer 7

Positron + neutrino released ( which is uncharged)

Question 8

How are positron-emitting isotopes made?

Answer 8

» They do not occur naturally

» Manufactured by placing a stable isotope in liquid or solid form - in the path of a beam of protons - some of the nuclei in the substance absorb extra protons and become unstable position - emitters

Question 9

What is rest energy?

Answer 9

» Rest energy is the mass of a particle when it is stationary corresponds to rest energy locked up as mass

Question 10

What is the notation for rest energy?

Answer 10

» m(o)c^2

Question 11

What must be included in the conversation of energy?

Answer 11

» Rest energy must be included in the conversation of energy.
» Dirac predicted the existence of antimatter particles that would unlock the rest energy when they would meet and annihilate

Question 12

What did Dirac’s theory of antiparticles predict?
For every type of particle there is a corresponding antiparticle that:

Answer 12

» Annihilates the particles and itself if they convert their total mass into photons

» Has exactly the same rest mass as the particle

» Has exactly the opposite charge to the particle if the particle has a charge

Question 13

What is pair production?

Answer 13

» Dirac predicted that a photon with sufficient energy passing near a nucleus or an electron can suddenly change into a particle-antiparticle pair ,which would then separate from each other

Question 14

What is 1 MeV equal to?

Answer 14

» 1.60 x 10^-13

Question 15

What is the definition of one electron volt?

Answer 15

» Defined as the energy transferred when an electron is moved through a potential different of 1 volt

Question 16

When does annihilation occur?

Answer 16

» occurs when a particle and a corresponding antiparticle meet and their mass is converted into radiation energy

Question 17

What is produced as a result of annihilation?

Answer 17

» 2 photons are produced in this process

Question 18

Can a single photon be produced?

Answer 18

» No as a single photon cannot ensure a total momentum of zero after the collision

Question 19

What is the minimum energy of each photon in annihilation?

Answer 19

» hf(min) = E(o) where E(o) is the rest energy of the particle
» Energy of photon = hf, and Energy = Mc^2, when mass is 0 Energy = Energy(o)

Question 20

What is the minimum energy of photon needed in pair production?

Answer 20

» hf(min) = 2E(o)

Question 21

What are the four fundamental forces?

Answer 21

» Gravity
» Electromagnetic
» Weak force
» Strong nuclear

Question 22

What are forces between particles caused by?

Answer 22

» Exchange particles

Question 23

What is the rest energy of an electron in MeV?

Answer 23

» 0.511 MeV

Question 24

Describe the changes that take place in a proton-rich nucleus when it emits a positron?

Answer 24

» Proton changes into a neutron
» And a positron and neutrino is released

Question 25

What are the 2 ways in which pair production of a positron and an electron differs from positron emission?

Answer 25

» No photon involved in positron emission
» In pair production only photons are emitted, no neutrinos

Question 26

Why is the energy after collision more?

Answer 26

» The energy associated with the rest masses
must be added

Question 27

If the kinetic energy is greater what is the effect on the subatomic particles produced?

Answer 27

» Be more massive
» Have greater kinetic energy