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aqa a level physics > particles and radiation > Flashcards

particles and radiation Flashcards

1
Q

Approximate size of an atom

A

radius of 0.1nm

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2
Q

define ‘isotope’

A

atoms of an element with the same number of protons but different number of neutrons

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3
Q

what is isotopic data? what is its use?

A

The relative amounts of different isotopes of an element found within a substance. Can be used to approximate the age of archaeological finds

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4
Q

How was it deduced that the strong force must exist?

A

The electromagnetic force acts within the nucleus causing repulsion between the similarly charged protons. This is much stronger than the gravitational force acting between all nucleons (due to their mass). If no other forces were present, nucleons would fly apart

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5
Q

Range of the strong force?

A

repulsive at very short range <0.5fm
attractive up to 3fm
negligible afterwards
(very short range)

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6
Q

1fm

A

1 * 10^-15m

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7
Q

What particles experience the electromagnetic force?

A

charged particles

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8
Q

What particles experience the strong nuclear force?

A

hadrons

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9
Q

range of the electromagnetic force

A

infinite

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10
Q

what is nuclear decay

A

unstable nuclei emitting particles to become more stable

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11
Q

describe alpha decay

A

When the nuclei of an atom is too big for the strong nuclear force to keep them stable
they emit an alpha particle (He)

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12
Q

range of an alpha particle

A

short range - few cm in air

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13
Q

How can we observe the range of an alpha particle?

A

Geiger counter - bring it close to a source of alpha radiation and move away. watch count rate drop after a few cm
cloud chamber - alpha particles leave tracks

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14
Q

describe beta minus decay

A

occurs in neutron rich isotopes
the nucleus ejects a beta particle ( fast-moving electron ) and in turn a neutron in the nucleus becomes a proton
an antineutrino is released and carries away some momentum and energy

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15
Q

range of beta particle

A

can travel up to a several metres through air

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16
Q

What led to the hypothesis of neutrinos?

A

to account for conservation of energy
kinetic energies of beta particles varied up to a maximum
had to be neutral so charge was conserved
had to have almost zero mass as it hadn’t been detected

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17
Q

Electromagnetic spectrum

A

radio, micro, IR, visible, UV, x-rays, gamma

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18
Q

frequency

A

number of complete waves passing a point per second

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19
Q

wavelength

A

distance between adjacent crests of wave

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20
Q

the higher the frequency of electromagnetic radiation…

A

the greater its energy

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21
Q

photon energy {}

A

E = hf E = hc/λ

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22
Q

define work function [2]

A

Energy required to remove an electron
Minimum energy required to remove an electron from a (metal) surface

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23
Q

What is meant by an antiparticle [2]

A

Particle with equal (rest) mass/energy
but opposite charge/baryon number/lepton number

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24
Q

how does an antiparticle compare with its corresponding particle?

A

They have the same mass and rest energy
opposite charge

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25
Q

What does the formula E=mc^2 refer to?

A

pair production
energy converted into mass, equal amount of matter and antimatter are produced

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26
Q

what are photons?

A

packets of EM radiation

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27
Q

When in an applied magnetic field why do corresponding particles of matter and antimatter curve ?

A

They have opposite charges hence they curve away from each other

28
Q

How do you calculate the minimum energy needed for pair production?

A

total rest energy of the particles produced
Emin = 2E0

29
Q

1ev in J

A
  • 1.6 * 10^-19
30
Q

1Mev in J

A
  • 1.6 * 10^-13
31
Q

Why are electron-positron pairs more likely to be produced than proton antiproton pairs?

A

They have a relatively low mass
low mass -> low rest energy
so less energy required for pair production

32
Q

Mev -> ev

A
  • 10^6
33
Q

what is annihilation

A

when a particle meets its corresponding antiparticle
all mass of the particle and the antiparticles are converted back to energy ( 2 gamma ray photons )

34
Q

How do you calculate the energy of the gamma ray photons produced in annihilation?

A

energy of the pair = 2E0
produces two gamma ray photons
so each gamma ray photon will have energy E0

35
Q

What is an application of annihilation?

A

PET scanners
positron emitting isotope in bloodstream
positrons will annihilate with electrons giving off gamma rays which can easily be detected (they also move in opposite directions so can be distinguished)

36
Q

What are the four fundamental forces?

A

weak
strong nuclear force
electromagnetic
gravitational

37
Q

what is a hadron

A

a particle that experiences the strong nuclear force
( subject to the strong interaction )
made up of quarks

38
Q

what are the two types of hadrons and what are they made up of

A

baryons
3 quarks

mesons
quark antiquark pair

39
Q

What do all baryons eventually decay to and why?

A

All baryons can be unstable except protons, so they eventually decay to become a proton which is stable

40
Q

what is baryon number?

A

a quantum number that must be conserved
it is the number of baryons
protons, neutrons have baryon number +1
antibaryons -1
other particles 0

41
Q

neutron decay

A

n –> p + e~ + V~
weak interaction

42
Q

what are mesons?

A

are all unstable
have baryon number 0 , quark anti-quark pair
they interact with baryons via the strong force

43
Q

what are the lightest mesons

A

pions
exchange particle of the strong nuclear force
π±, π0

44
Q

What are the heavier mesons

A

kaons
have a strange quark
have a short lifetime and decay into lighter pions
K±, K0

45
Q

waffle about cosmic rays detecting mesons

A

high energy particles from space known as cosmic rays interact with molecules in the atmosphere and produce mesons
these leave tracks in a cloud chamber

46
Q

what are leptons

A

fundamental particles
don’t feel the strong nuclear force, interact via the weak interaction
( and em and g a bit, em if charged )

47
Q

which leptons are stable and unstable

A

electrons are stable leptons
unstable leptons include muons, tauons, . they are essentially heavy electrons
they eventually decay into electrons

48
Q

describe neutrinos

A

both electrons and muons have their constituent neutrinos,
and antineutrinos
they have virtually zero mass
no charge

neutrino - lepton number +1
antineutrino - lepton number -1

lepton electron number and lepton muon number

49
Q

lepton number of a muon antineutrino

A

electron lepton number 0
muon lepton number -1

50
Q

what are strange particles?
how are they created

A

have a property called strangeness
created via the strong interaction

51
Q

when is strangeness conserved

A

not in the weak interaction

52
Q

strangeness of K+ K-

A

+1 -1

53
Q

via which interaction do strange particles decay

A

weak ( strangeness isn’t conserved )

54
Q

what properties need to be conserved in particle interactions?

A

charge
energy
momentum
baryon/lepton number
strangeness ( not in weak )

55
Q

what are quarks

A

fundamental particles
they are the building blocks for hadrons

56
Q

baryon number of the quarks

A

up 1/3
down 1/3
strange 1/3
everything else 0

57
Q

strange number of the quarks

A

up 0
down 0
strange -1
everything else 0

58
Q

charge of the quarks

A

up +2/3
down -1/3
strange -1/3

59
Q

which quarks make up pions

A

[π0] up, anti-up
[π0] down, anti-down
[π+1] up, anti-down
[π-1] down, anti-up

60
Q

what are the four possible kaons

A

[K-] anti up strange
[K0] antidown strange
[K+] up antistrange
[K0] down antistrange

61
Q

is it possible to have just 1 quark

A

quark confinement is not possible
pair production occurs instead

62
Q

describe the process of beta minus and plus decay

A

udd -> uud + e~ + v~
neutron -> proton
change of quark character

uud -> udd + e+ + v
proton -> neutron

63
Q

what can forces also be described as

A

particle exchange

64
Q

electrostatic repulsion is caused by what?

A

the exchange of virtual photons
transfer energy, momentum
they are short lived

65
Q

how is the range of a force determined

A

the size of the exchange particle
heavier exchange particles have shorter range
virtual photon has virtual zero mass, infinite range of em
w bosons have a mass 100 times as big as a proton’s so weak force very short range

66
Q

what is electron capture and how does it differ to electron-proton collision

A

when a proton rich nuclei captures an electron from the inner shells of an atom and use it to become a neutron

electron capture has w+ boson going right ->
electron proton collision has w- boson going left <-

67
Q

what is the exchange particle of electromagnetic repulsion

A

virtual photon

aqa a level physics (10 decks)

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