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Physics > Unit 2 Particles and Radiation > Flashcards

Unit 2 Particles and Radiation Flashcards

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1
Q

What is the specific charge of a particle?

A

Ratio of its charge to mass. (charge/mass = specific charge)

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2
Q

What is the proton number?

A

The proton number is the number of protons in the nucleus, denoted by Z.

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3
Q

What are isotopes?

A

Atoms of the same element with the same number of protons but different number of neutrons.

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4
Q

What can isotopic data for the amount of carbon -14 in organic matter be used for?

A

To calculate the age of archaeological finds.

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5
Q

What can isotopic data about a material provide?

A

It can provide the ratio of different isotopes that occur in it.

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6
Q

What does the strong nuclear force do in the nucleus?

A

Provides the force needed to keep the nucleus stable by balancing the electrostatic repulsion between protons. It has short range attraction (up to ~3fm) and very short range repulsion (closer than ~0.5fm).

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7
Q

What kind of nuclei emit nuclear radiation?

A

Unstable atomic nuclei, to become more stable as they have too many neutrons in the first place.

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8
Q

If an unstable nuclei undergoes alpha decay, what is emitted from the nucleus?

A

An alpha particle - two protons and two neutrons.

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9
Q

If an unstable nuclei undergoes beta - decay, what is emitted from the nucleus?

A

A fast moving electron and an electron antineutrino.

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10
Q

What are the products of beta - decay?

A

New nucleus + electron + electron antineutrino

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11
Q

What are the products of beta + decay?

A

New nucleus + positron + electron neutrino

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12
Q

If an unstable nuclei undergoes gamma radiation, what is emitted from the nucleus?

A

A gamma ray with a short wavelength and high frequency. (EM radiation)

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13
Q

Why does the neutrino exist?

A

The existence of the neutrino was hypothesised to account for the conservation of energy in beta decay. Essentially a certain amount of energy should be conserved by beta decay but beta particles had a range of energies instead of one value - neutrino emitted to ‘carry away’ excess energy.

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14
Q

What can you conclude from the equation E= mc^2 ?

A

That mass can be converted to energy and vice versa.

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15
Q

What happens when a particle and an antiparticle meet?

A

Annihilation - all the mass of the particle and antiparticle is converted into photons of electromagnetic radiation that travel in opposite directions.

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16
Q

How many photons are released in annihilation and why?

A

At least two photons, because one photon would not allow momentum to be conserved.

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17
Q

What is the minimum energy of both photon produced in annihilation?

A

hf(min)= 2E0 where E0 is the rest energy of the particle/antiparticle

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18
Q

What is pair production?

A

A high energy photon converts into a particle and its antiparticle. Energy is converted into mass.

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19
Q

What is the minimum energy of a photon to undergo pair production?

A

hf(min) = 2E0 where E0 is the rest energy of the particle/antiparticle

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20
Q

Name the four fundamental forces

A

Gravity, electromagnetic, strong nuclear, weak nuclear

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21
Q

What are the properties of the gravitational force and its exchange particle?

A

An attractive force between any two objects due to their mass

Graviton

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22
Q

What are the properties of the electromagnetic force and its exchange particle?

A

Acts between objects with charge, repulsive when charge is the same and attractive when charges are opposite

Virtual photon

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23
Q

What are the properties of the strong nuclear force and its exchange particles?

A

Only acts on a set of particles called hadrons which holds the protons and neutrons together in a stable nucleus.

Gluons for quark interactions and pions for all other interactions.

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24
Q

What are the properties of the weak nuclear force and its exchange particle?

A

Extremely short range force that acts on the hadrons and leptons and is involved in beta +/- decay, electron capture and electron-proton collisions.

W -/+ bosons.

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25
Q

What are the properties of hadrons?

A

They are affected by the strong nuclear force.
They are not fundamental as they are made up of quarks.

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26
Q

What are the properties of baryons?

A

They are made up of three quarks.
They eventually decay into protons (most stable hadron)

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26
Q

What are the two classes of hadrons?

A

Baryons and mesons

27
Q

Name some baryons.

A

Protons
Neutrons
Sigma Particle

28
Q

What are the properties of mesons?

A

They are made up of one quark and antiquark.
They are unstable and do not include protons in their decay products.

29
Q

Name some mesons.

A

Pions, Kaons

30
Q

What are the properties of the Kaons?

A

They have a short lifetime.
They decay into pions.

31
Q

What is the decay equation of a muon?

A

Muon - electron + electron neutrino + muon neutrino

32
Q

Which of the two main groups of particles contains only fundamental particles?

A

Leptons

33
Q

What are the properties of leptons?

A

They are not affected by the strong nuclear force.
They can change into other leptons via the weak interaction.

34
Q

Which particles can be classified as leptons?

A

Electrons, muons, electron neutrinos, muon neutrinos

35
Q

Which quantities are always conserved in particle interactions?

A

Energy, momentum, charge, baryon number, lepton numbers

36
Q

What are the properties of strange particles?

A

Strange particles are always produced through the strong interaction, so are always created in pairs to conserve strangeness.

They always decay through the weak interaction.

37
Q

Which quantity is conserved in strong interactions but not in weak interactions?

A

Strangeness

38
Q

What values does strangeness take?

A

From -3 to +3 for hadrons, 0 for leptons

39
Q

What values can strangeness change by in weak interactions?

A

Strangeness can change by 0, +1 or -1 in weak interactions.

40
Q

What are anti hadrons made up of?

A

Antiquarks

41
Q

What must the total charge, baryon number and strangeness of a hadron be equal to?

A

Sum of these values for the three quarks of which it is composed (always integers)

42
Q

Give the quark composition of a proton

A

uud

43
Q

Give the quark composition of a neutron.

A

udd

44
Q

What is the quark composition of a sigma Σ particle?

A

Any combination of three quarks, must contain a strange particle

45
Q

What is the change of quark character in β− decay?

A

A neutron changes into a proton so a down quark changes into an up quark via the weak interaction.

46
Q

What is the change of quark character in β+ decay?

A

A proton changes into a neutron so an up quark changes into a down quark via the weak interaction.

47
Q

What is the photoelectric effect?

A

Emission of electrons from the surface of a metal when electromagnetic radiation above a certain frequency is incident on it.

48
Q

Define the threshold frequency of a metal?

A

Minimum frequency of photons needed for photoelectric emission of electrons from the metal

49
Q

What is the work function of a metal?

A

The minimum energy an electron needs to break bonds and escape from the metal surface.

50
Q

What is the stopping potential?

A

Stopping potential is the minimum potential needed to stop photoelectric emission.

51
Q

What is the excitation of an atom?

A

An electron moves up one or more of the energy levels in an atom

52
Q

When an electron moves down one or more energy levels in an atom, what does it emit?

A

Energy in the form of a photon.

53
Q

What do each of the coloured lines in a line emission spectrum correspond with?

A

A particular wavelength (and therefore frequency) of light emitted by the source

54
Q

When does ionisation occur?

A

When an electron gains enough energy to leave the atom.

55
Q

What is the ionisation energy?

A

The amount of energy needed to remove an electron from the ground state of an atom.

56
Q

What is the ground state?

A

The lowest energy an electron can have in the atom.

57
Q

If a wave has a long wavelength, what can be said about its energy?

A

Low energy

58
Q

If a wave has a short wavelength, what can be said about its energy?

A

High energy

59
Q

Define an electron volt?

A

Energy gained by an electron accelerated through a potential difference of 1V.

60
Q

Describe how a fluorescent tube emits visible light.

A

The fluorescent tube is filled with mercury vapour. When a high voltage is applied to the tube, it accelerates free electrons. The mercury atoms are ionised and excited as they collide with each other and with electrons in the tube. They then emit UV photons which are absorbed by atoms of the fluorescent coating and become excited. The excited atoms in the coating de-excite in steps and emit visible photons making the tube glow.

61
Q

Identify the phenomena that can only be explained by the wave model of light.

A

Diffraction and interference

62
Q

What did de Broglie propose about the nature of particles?

A

All matter particles have wave properties

63
Q

How does a PET scanner work?

A

The patient is injceted with a radioactive tracer that undergoes beta + decay. The tracer is attached to a molecule that collects in a tumour. When nuclei in the tracer decay, they emit positrons. When a positron meets an electron they are annihilated and two gamma rays are emitted. The PET scanner detects the gamma rays and calculates where the radiation came from. The PET scanner moves around the patient to detect lots of pairs of gamma ray. A computer builds up an image of the inside of the patient.

64
Q

Why must the photon have at least a certain frequency for pair production to occur?

A

A certain amount of energy is needed to convert into the minimum mass required. The energy of the photon depends on the frequency.

65
Q

Why does the pair production happen close to a nucleus?

A

To conserve momentum. The nucleus will recoil with the same momentum as the momentum of the new particle and antiparticle.

Physics (10 decks)

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