1.4 - Particles And Antiparticles

Question 1

what happens when matter and antimatter particles meet

Answer 1

they destroy each other and radiation is released

Question 2

how do we make use of this effect

Answer 2

positron emitting tomography (PET) hospital scanner

Question 3

what is the positron

Answer 3

antiparticle of the electron

Question 4

what happens when a PET scan is done on the brain

Answer 4

A positron emitting isotope administered to the patient and some of it reaches the brain via the blood system.
Each positron emitted travels no further than a few millimetres before it meets an electron and they annihilate each other.
Two gamma photons, produced as a result, are sensed by detectors linked to the computer and gradually an image is built up from the detector signals of where the positron emitting nuclei are inside the brain.

Question 5

when does positron emission take place

Answer 5

when a proton changes into a neutron in an unstable nucleus with too many protons

Question 6

what is the symbol of a positron and what is its charge

Answer 6

+1B positive as it is the antiparticle of the electron

Question 7

what is a antiproton

Answer 7

the antiparticle of the proton

Question 8

what is an antineutron

Answer 8

the antiparticle of a neutron

Question 9

do positron emitting isotopes occur naturally

Answer 9

no

Question 10

how are positron emitting isotopes made

Answer 10

manufactured by placing a stable isotope ,in a 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 positron emitters

Question 11

when and who predicted antimatter

Answer 11

1928 by English physicist Paul Dirac before the first antiparticle (positron) was discovered

Question 12

what happened 20 yrs after Dirac

Answer 12

Einstein had shown that the mass of a particle increases the faster it travels creating the E=mc^2 equation

Question 13

what did Einstein say that the rest mass of a particle corresponds to

Answer 13

rest energy locked up as mass and showed that the rest energy must be included in the conservation of energy

Question 14

Dirac predicted the existence of anti particles that would unlock rest energy when ……

Answer 14

a particles and a corresponding antiparticle meet and annihilate eachother

Question 15

Dirac theory of antiparticles predicted the for every type of particle there is a corresponding anti particle that

Answer 15

• annihilates the particle and itself if they meet, converting there total mass into protons
• has exactly the same rest mass as the particle
• has exactly the opposite charge to the particle if the particle has a charge

Question 16

what did Dirac also predict

Answer 16

the opposite process of pair production
He predicted that a photon with sufficient energy passing near a nucleus or a electron can suddenly change into a particle - antiparticle pair which would then separate from each other

Question 17

what is the energy of a particle/antiparticle often expressed in

Answer 17

MeV

Question 18

what does 1 MeV =

Answer 18

1.60 x 10^-13 J

Question 19

what is one electron vault defined as

Answer 19

the energy transferred when an electron is moved through a potential of 1 vault

Question 20

when does annihilation occur

Answer 20

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

Question 21

what is produced for annihilation

Answer 21

2 photons (a single photon cannot ensure a total momentum of 0 after the collision)

Question 22

how do you calculate the minimum energy of each photon produced

Answer 22

hfmin = E0
the minimum energy of the 2 photon = hfmin
E0 = rest energy of the particle

Question 23

what happens in pair production

Answer 23

a photon creates a particle and a corresponding antiparticle and vanishes in the process

Question 24

minimum energy of a photon needed to create pair production

Answer 24

hfmin = 2E0

Question 25

what can you see the path of an alpha and a beta particle using

Answer 25

a cloud chamber
transparent container containing air saturated with vapour and made very cold like high in the atmosphere

Question 26

what do ionising particles leave behind them in a cloud chamber

Answer 26

a trail of liquid droplets

Question 27

in 1932 what did carl Anderson use the cloud chamber to do

Answer 27

take photos of the trails produced by cosmic rays as they passed through a lead plate within a magnetic field

Question 28

what 2 things should happen to the particles in the cloud chamber

Answer 28

bend towards the magnetic field depending on wether the particles are positive or negative

when the particles are going slower they should bend so should bend ore after going through plate due to loss of kinetic energy

Question 29

how did Dirac discover the positron

Answer 29

sent a beta particle into the chamber however it bent towards the wrong pole so was therefore a positron