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Particles 1 Flashcards

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1
Q

Define nucleons

A

The number of protons and neutrons in the nucleus of an atom

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2
Q

Describe how electrons are located in an atom

A

They orbit the nucleus in different energy levels/shells

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3
Q

Define specific charge

A

The charge to mass ratio (charge/mass)

units are CKg^-1

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4
Q

Describe the symbols which show the element and its proton and nucleon numbers

A

The big X is the element
To the left of the X, there is a small A (nucleon number) at the top and a small Z (proton/atomic number) at the bottom

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5
Q

Define an isotope

A

Isotopes are atoms with the same number of protons but different number of neutrons

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6
Q

Describe a use of isotopes

A

Carbon dating:
Carbon-14 is a radioactive isotope of carbon and every living thing starts with the same amount. Therefore, using the half-life and knowing how much C-14 is left, we can work out its age

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7
Q

Explain the purpose of the SNF

A
  • Gravity is much weaker than electrostatic forces and protons in the nucleus have the same charge so the SNF stops them from repelling and the nucleus flying apart
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8
Q

Explain how the SNF changes at different separations, how can this be shown on a graph

A
  • The force is repulsive below 0.5 fm to stop the nucleus imploding since the SNF is much stronger than the electrostatic force
  • The force is attractive between 0.5 and 3 fm to stop the nucleus exploding
  • The force has no affect after 3 fm
  • There is a graph which shows this with force between nucleons on the y axis and separation on the x axis where the positive y direction is repulsive and negative y direction is attractive
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9
Q

Define an unstable nuclei, how can the nuclei become stable

A
  • A nuclei with too many protons, neutrons or both that the SNF is not enough to keep them stable or the nucleus has too much internal energy
  • Therefore, they undergo radioactive decay to become stable
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10
Q

Explain alpha decay, mentioning when it happens, and the affect on the nucleus

A
  • Occurs in large nuclei with too many protons and neutrons
  • The decay causes the proton number to decrease by 2 and nucleon number to decrease by 4, which 1 alpha particle (or a helium nucleus)
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11
Q

Explain beta minus decay, mentioning when it happens and the affect on the nucleus

A
  • Occurs in neutron rich nuclei
  • Neutron turns into proton, which releases a beta particle (electron) and anti electron neutrino
  • The mass number stays the same, but the proton number increases by 1
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12
Q

How was the anti-electron neutrino discovered

A
  • Calculations involving beta decay showed that without another particle, energy would not be conserved
  • neutrinos were hypothesised to account for this and they were later observed
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13
Q

Define an antiparticle, giving examples

A

Every particle has an antiparticle, which has the same rest energy and mass, whilst every other property (e.g. charge) is the opposite
- examples of particle and antiparticle pairs are electron and positron or electron neutrino and anti electron neutrino

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14
Q

Explain how EM radiation travels

A

In packets called photons

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15
Q

Describe the relationship between the energy of a photon and the frequency of the em radiation

A

E=hf (=hc/λ)

directly proportional where Planck’s constant is 6.63x10^-34 Js. (It is Js because it is E/f and f=1/T

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16
Q

Explain annihilation

A
  • According to E=mc^2, mass can be converted into energy
  • This is shown when a particle and antiparticle collide and their masses are converted to energy
  • This energy is released as 2 gamma photons travelling in opposite directions to conserve momentum
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17
Q

How could you calculate the energy of the gamma photons released in annihilation

A

each photon has energy of hf = (2Erest +Ek)/2

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18
Q

Describe an application of annihilation

A

PET scanners work by emitting positrons into a patient, which annihilate with electrons, which releases gamma photons, which can be detected easily by a computer in order to produce 3d images

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19
Q

Explain pair production

A
  • According to E=mc^2, energy can be converted to mass
  • This is shown in pair production where a photon is converted to a particle and antiparticle pair in the presence of a nucleus
  • The energy of the photon has to be ≥ the energy of the 2 particles produced. Excess energy is converted to kinetic energy
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20
Q

What happens to the positron shortly after pair production

A

It will annihilate with another electron, producing 2 photons travelling in opposite directions to conserve momentum

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21
Q

Why is the presence of a nucleus required for pair production to occur

A
  • Pair production only occurs when the photon interacts with an electric field, which is provided by the nucleus (caused by charged protons)
  • If there was no nucleus, the momentum of the particles would be less than the momentum of the photon so the nucleus absorbs the excess momentum
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22
Q

How would you calculate the energy of the photon during pair production

A

E = hf = 2Erest + KE

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23
Q

What are the 4 fundamental forces

A

gravity, electromagnetic, weak nuclear and strong nuclear

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24
Q

Define exchange particles

A

Exchange particles are the force carriers of the fundamental forces, which carry energy, momentum, force and charge between particles.

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25
Q

List the exchange particle, range and “what it acts on” for each fundamental force

A

Strong nuclear - gluon, 3 fm, hadrons

Weak nuclear - W bosons, 10^-18 m, all particles

Electromagnetic - virtual photon, infinite, charged particles

Gravitational - graviton, infinite, particles with mass

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26
Q

Why do different exchange particles (gauge bosons) have different ranges

A

If the boson has a larger mass, it requires more energy to “exist”, so e.g. since the W boson has a mass 100x a proton, it can only exist for a very short time so it has a very short range. Whereas a photon has zero mass so an infinite range

27
Q

Which reactions is the weak nuclear force responsible for

A
  • Beta minus
  • Beta plus
  • Electron capture
  • Electron - proton collision
28
Q

Explain electron capture

A
  • Occurs in proton rich and neutron deficient nuclei
  • a proton from the nucleus captures and absorbs an inner shell electron, this causes the proton to turn into a neutron
  • The mass number of the atom stays the same but the atomic number decreases by 1
  • An electron neutrino is also released to conserve energy and during the process a W+ boson is exchanged from the proton to electron
29
Q

Explain electron proton collision

A
  • occurs when an electron and proton collide
  • The electron turns into an electron neutrino and the proton turns into a neutron
  • Mass number stays the same, atomic number decreases by 1
  • During the process, a W- boson is exchanged from the electron to the proton
30
Q

What are the rules for drawing a Feynman diagram

A

1) The incoming particles start from the bottom and move up to the middle and the outgoing particles start from the middle and move up to the top
2) The baryon and lepton number are conserved on each side of the boson and baryons and leptons don’t cross
3) W bosons carry charge from one side to the other so W- going one way is the same as a W+ going the other way

31
Q

What does electromagnetic repulsion look like on a feynman diagram

A

e.g. 2 electrons come from the bottom, virtual photon would exchange the force between them, they would come out the top moving away from each other

32
Q

Explain beta plus decay, mentioning when it happens, and how it affects the nucleus

A
  • Occurs in proton rich nuclei
  • Proton turns into a neutron, which releases a positron (beta-plus particle) and an electron neutrino
  • Mass number stays the same but proton number decreases by 1
33
Q

How can you show beta minus decay on a Feynman diagram

A
  • Neutron comes from the bottom, proton leaves moving out of the same side (because they are baryons)
  • The boson is a W- boson because it carries the charge difference of -1 between the proton and neutron
  • the boson then decays into the electron and anti electron neutrino, which are released from the other side of the boson.
34
Q

How can you show beta plus decay on a Feynman diagram

A
  • proton comes up from the bottom, neutron goes out from the same side
  • The charge difference is carried off by the W+ boson, which decays into the positron and electron neutrino
35
Q

Explain the difference between hadrons and leptons

A
  • Lepton are fundamental particles becase they cannot be broken down further whereas hadrons are not because they can be broken down into quarks (the other type of fundamental particle)
  • Hadrons are particles that can feel the SNF so leptons cannot feel it
36
Q

What are the different types of hadrons

A
  • Baryons (and antibaryons)
  • Mesons
37
Q

Explain the difference between a baryon and a meson

A
  • baryons (and antibaryons) are made up of 3 quarks or 3 antiquarks
  • Mesons are made up of a quark and an antiquark
38
Q

Give examples of baryons and mesons

A

Baryons - protons and neutrons (or antiprotons and antineutrons)
Mesons - pions and kaons

39
Q

What is the only stable baryon

A

The proton
- This means every baryon eventually decays into a proton, either directly or indirectly

40
Q

Which mesons are stable

A

No mesons are stable

41
Q

Give examples of leptons

A
  • electron
  • electron neutrino
  • muon
  • muon neutrino
  • All of the aboves antiparticles
42
Q

Which leptons are stable

A

Electrons/positrons and all neutrinos/antineutrinos

(every lepton except muons and anti-muons)

43
Q

Explain the baryon number of a particle

A
  • A baryon number of 1 means the particle is a baryon
  • A baryon number of -1 means the particle is an antibaryon
  • A baryon number of 0 means it is not a baryon
  • In an interaction, the baryon number is always conserved so an interaction is impossible if it is not
44
Q

Explain the lepton number of particle

A
  • A lepton no. of 1 means it’s a lepton
  • A lepton no. of -1 means it’s an antilepton
  • A lepton no. of 0 means it’s not a lepton
  • There are 2 types of lepton no.; electron lepton no. and muon lepton no. so they are counted separately
  • The lepton number is always conserved so an interaction is impossible if it’s not
45
Q

What is a role of pions within the nucleus

A

They are another exchange particle for the SNF

46
Q

Where were pions and kaons discovered

A

In cosmic rays

47
Q

Which of the pions or kaons are more heavy/unstable

A

kaons are heavier/more unstable as pions are the lightest meson

48
Q

Through what fundamental force do mesons interact with baryons

A

Via the strong nuclear force

49
Q

Through what fundamental forces do leptons interact

A
  • Mainly weak nuclear
  • But also gravitational and EM as well if the particles are charged
50
Q

Through what fundamental force do neutrinos interact

A
  • Only weak interaction
  • because they have no mass or charge and they are not hadrons
51
Q

Why and how do muons decay

A
  • They are known as heavy electrons so they are unstable
  • They eventually decay into an electron, an electron antineutrino and a muon neutrino
52
Q

Define a quark

A

The fundamental particles that make up hadrons

53
Q

What are the 3 types of quark/antiquark we need to know

A

1) up and anti-up
2) down and anti-down
3) strange and anti-strange

54
Q

Through which fundamental force are strange particles produced and decayed

A
  • They are produced through the SNF
  • They decay through the weak nuclear force
55
Q

What are the characteristics of a strange particle e.g. kaon

A

1) Created in pairs via the strong interaction
2) Decays into a combination of pions, proton and neutron
3) Decays via the weak interaction
4) Half life is unusually long (don’t say long life span)

56
Q

Why are strange particles produced in pairs

A
  • Strangeness is only conserved in strong interactions, it can change by 1, -1 or 0 in weak interactions
  • Therefore, if they are produced in strong interactions and strangeness needs to be conserved, 2 strange particles must be produced for the strangeness from each to cancel out e.g. K+ and K-
    Therefore, the overall strangeness is 0
57
Q

Give the symbol, charge, baryon number and strangeness for each quark

A

up - u, +2/3 , +1/3 , 0
down - d, -1/3 , +1/3 , 0
strange - s, -1/3 , +1/3 , -1

58
Q

Give the symbol, charge, baryon number and strangeness for each anti-quark

A

antiup - ū, -2/3, -1/3, 0
antidown - d(bar), +1/3, -1/3 , 0
antistrange - s(bar), +1/3 , -1/3 , +1

59
Q

How can you find the quark composition of a hadron

A
  • look at the final charge of a particle, eg π+ has +1 charge
  • if it is a baryon, find a combination of 3 up and down quarks which add up to the charge
  • if it is a meson, find a combination of a quark and an antiquark that add up to the charge (a kaon has a strange quark)
60
Q

What are the antiparticles of mesons

A

π- is the antiparticle of π+
π0 is the antiparticle of itself
K- is the antiparticle of K+

This means each pair has the opposite quark composition (quarks replaced with their antiquarks and vice-versa)

61
Q

In which interaction can a quark be changed

A

Weak interaction. This is is only type of interaction where this can happen

e.g.in beta minus decay, neutron -> proton so
d ->up

62
Q

List the 7 quantities that are conserved in interactions

A
  • energy is always conserved
  • momentum is always conserved
  • charge always conserved
  • baryon number is always
    conserved
  • electron lepton number is always conserved
  • muon lepton number is always conserved
  • strangeness is only conserved in strong interactions and can change by 1, -1, 0 in weak interactions
63
Q

How can particle physics experiments occur

A

The particles need to be travelling extremely fast. This can only be achieved using a particle accelerator, which are very expensive to build and run

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