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P1-PARTICLES AND RADIATION > 1.4 - PARTICLES AND ANTIPARTICLES > Flashcards

1.4 - PARTICLES AND ANTIPARTICLES Flashcards

1
Q

What happens when antimatter and matter particles meet?

A

they destroy each other and radiation is released

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2
Q

How do we make use of the effect when antimatter and matter particles meet?

A

in a positron emitting tomography (PET) hospital scanner

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3
Q

What does the P in PET stand for?

A

positron, which is the antiparticle of the electron

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4
Q

What happens when a PET scanner is used for a brain scan?

A

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

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5
Q

How long does each positron travel before it meets an electron?

A

each positron emitted travels no further than a few millimeters before it meets an electron

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6
Q

What happens when the positron and electron meet?

A

they annihilate each other

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7
Q

What is produced due to the annihilation?

A

two gamma photons

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8
Q

What senses the two gamma photons produced?

A

detectors linked to computers

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9
Q

What is gradually produced from the detector signals?

A

an image is built up from the detector signals of where the positron-emitting nuclei are inside the brain

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10
Q

When does positron emission take place?

A

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

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11
Q

What charge does a positron carry?

A

positive charge

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12
Q

Why does the positron carry a positive charge?

A

as it’s the antiparticle of the electron

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13
Q

What is the symbol for the positron?

A

β⁺

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14
Q

What else is emitted during the positron emission?

A

a neutrino

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15
Q

What is the charge of the neutrino?

A

uncharged

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16
Q

What is the symbol of the neutrino?

A

v

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17
Q

Are positron-emitting isotopes naturally occurring?

A

no

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18
Q

How are positron-emitting isotopes manufactured?

A

by placing a stable isotope, in liquid or solid form, in the path of a beam of protons

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19
Q

What happens to some of the nuclei in substance?

A

it absorbs extra protons and become unstable positron-emitters

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20
Q

When was antimatter predicted and by who?

A

in 1928 by the English physicist Paul Dirac

21
Q

In comparison to the positron when was the first antiparticle discovered?

A

before the first antiparticle the positron was discovered

22
Q

More than 20yrs earlier to the prediction of antimatter, what did Einstein show?

A

mass of a particle increases the faster it travels

23
Q

Which one of Einstein’s equations relate the energy supplied to the particle to its increase in mass?

A

E = mc^2

24
Q

What did Einstein most importantly say?

A

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

25
Q

What did Einstein show regarding rest energy?

A

rest energy must be included in the conservation of energy

26
Q

What did Dirac predict?

A

existence of antimatter particles that would unlock rest energy, whenever a particle and a corresponding antiparticle meet and annihilate each other

27
Q

Dirac’s theory of antiparticles predicted that for every type of particle there is a corresponding antiparticle that: (3)

A

annihilates that particle and itself if they meet, converting their 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

28
Q

What process, opposite to the annihilation process did Dirac predict?

A

pair production

29
Q

What did Dirac predict in the pair production process?

A

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

30
Q

How is the energy of a particle or antiparticle often expressed?

A

in millions of electron volts

31
Q

What is the unit for electron volts?

A

MeV

32
Q

How many joules does 1 MeV equal to?

A

1 MeV = 1.60 * 10^-13 J

33
Q

What is one electron volt defined as?

A

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

34
Q

When does annihilation occur?

A

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

35
Q

What is produced in the annihilation process?

A

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

36
Q

What is the minimum energy of each photon equated to?

A

the energy of the two photons, to the rest energy of the particle and of the antiparticle

37
Q

What happens in pair production?

A

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

38
Q

How can the path of alpha and beta particles be seen?

A

using a cloud chamber

39
Q

What is a cloud chamber?

A

small transparent container containing air saturated with vapour and made very cold

40
Q

Where else does the same conditions as in the cloud chamber exist?

A

high in the atmosphere

41
Q

What do ionising particles leave?

A

a visible trail of liquid droplets when they pass through the air

42
Q

What did the American physicist Carl Anderson do in 1932?

A

used a cloud chamber and a camera to photograph trails produced by cosmic rays

43
Q

What did Carl Anderson decide to see?

A

if the particles could pass through a lead plate in the chamber

44
Q

What did he apply to the chamber and why?

A

with a magnetic field applied, he knew the trail of a charged particle would bend in the field

45
Q

What would happen to a positive particle?

A

deflected by the magnetic field in the opposite direction to a negative particle travelling in the same direction

46
Q

How did the speed affect the particle?

A

the slower it went, the more it would bend

47
Q

What did he think would happen if a particle went through the plate?

A

he thought it would be slowed down so its trail would bend more afterwards

48
Q

What did he actually discover?

A

a beta particle that slowed down but bent in the opposite direction to all the other beta trails he had photographed

49
Q

What momentous discovery did he make?

A

a positron, the first antiparticle to be detected

P1-PARTICLES AND RADIATION (6 decks)

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