Particles 1 Flashcards
How big is a nucleus?
approx diameter: 10^-14m/10^-15m
How big is an atom?
approx diameter: 10^-10m
Define a nucleon
A constituent particle of a nucleus: a proton or neutron
Define a nuclide
A specific isotope of a nucleus
Give an example of a nuclide
C-14 and C-12 are isotopes of carbon but they are different nuclides
Define an isotope
a nucleus with the same number of protons but a differing number of neutrons
What is meant by specific charge?
the charge per unit mass
How do you calculate specific charge?
specific charge = (net charge) / (total mass)
What is an ion?
a charged atom
a Ca
b
has how many protons, neutrons and electrons?
protons: b
neutrons: a - b
electrons: b
What is the nucleon number?
the number of protons and neutrons in the atom
At less than ____ the strong nuclear force is ______
0.5 fm
repulsive
Between ____ and ____ the strong nuclear force is _______
0.5 fm
3.0 fm
attractive
Beyond ____ the strong nuclear force is ____
3.0 fm
zero
(In the nucleus) The electromagnetic force just acts between the ______ and is therefore ______
protons
repulsive
The electromagnetic force is much ______ than the strong nuclear force
weaker
The strong nuclear force acts between all of the _____ and has nothing to do with _____
nucleons
charge
What is an alpha particle?
a helium nucleus
What is the mass number?
the number of protons + the number of neutrons
What is the atomic number?
the number of protons
What is the atomic and mass number of an alpha particle?
mass number - 4
atomic number - 2
What is an alpha particle in terms of the energy it holds?
mono-energetic
What is a beta particle?
an electron
What is a beta particle in terms of the energy it holds?
has a range on energies
What did the fact that an electron has a range of energies lead to the discovery of?
an antineutrino
What does an antineutrino do in beta decay?
shares the energy with the beta particle
Give three properties of a neutrino
1) neutral
2) very small mass (possibly mass-less)
3) therefore interacts very weakly
(shares energy with electron in beta decay)
Define a photon
a discrete amount of energy that forms EM radiation with both particle and wave properties
What is the electromagnetic spectrum in order of ascending frequency?
1) radio
2) micro
3) infrared
4) visible light
5) ultra-violet
6) x-ray
7) gamma
Define 1 electrovolt
the energy an electron gains when it moves through a potential difference of 1V
What is 1 eV equal to in Joules?
1 eV = 1.6 x 10^-19 J
What is rest energy?
Energy due to mass
Describe pair production by a photon
1) a photon collides with a nucleus (the nucleus so that momentum is conserved)
2) if the photon has sufficient energy, a particle and an antiparticle are formed
What is the minimum energy of the photon equal to in pair production?
Emin = hf min = 2Eo
Why is the minimum energy needed in pair production equal to 2Eo?
- charge has to be conserved during the collision
- so two particles need to be made (a particle and an antiparticle)
Explain why there is a minimum energy required in pair production by a photon
1) energy of the photon needs to provide at least the rest masses
2) this is the energy needed to produce both a particle and an antiparticle of velocity 0
3) as the particle and the antiparticle have rest energies
What equation shows the energy in pair production by a photon?
hf = 2Eo + KE
If a photon of a higher energy is used in pair production, compared to a photon of lower energy, what are the two possible differences in the particles produced?
1) could make more particles
2) could make the same number of particles but with more KE
When does annihilation occur?
When a particle meets its antiparticle
Define annihilation
the process by which a particle and its antiparticle meet and their mass gets converted into energy in the form of a pair of photons
Why are two photons produced in annihilation?
To conserve momentum
What equation shows the energy in annihilation?
2Eo (+ KE) = 2hf
Define a quark
a fundamental particle that makes up hadrons
Define a hadron
a composite subatomic particle made of two or more quarks held together by the strong nuclear force
Give an example of a hadron
proton
neutron
Define a baryon
a type of composite subatomic particle which contains three quarks (belong to the hadron family of particles)
Define a meson
hadronic subatomic particle composed of a quark-antiquark pair
Give an example of a meson
- pion
- kaon
Define a lepton
a fundamental particle that does not interact via the strong nuclear force
(feels the weak force but not the strong force)
Give 4 examples of a lepton
1) electron
2) electron neutrino
3) muon
4) muon neutrino
What is the only stable free baryon?
the proton
What are cosmic rays?
very high energy particles from space
The existence of the neutrino was hypothesised to account for…
conservation of energy in beta decay
What are the two classes of hadrons?
1) baryons
2) mesons
What do all baryons eventually decay to?
a proton
What does a muon decay into?
an electron
Define a pion
a type of meson that contains no strange quarks, it is the exchange particle of the strong nuclear force
Define a kaon
a type of meson which consists of one up or down quark and one strange quark, they decay into pions
What do kaons decay into?
pions
What is a boson?
a force carrying particle
Define fundamental particles
particles that are indivisible
The electromagnetic force affects all particle categories if they…
are charged
What must be conserved in all interactions?
- energy
- momentum
- charge
- baryon number
- lepton electron number
- lepton muon number
Weak interactions cause quarks to…
decay (change flavour)
Strong interactions cause _____________ of quarks
pair production
Strangeness gives particles…
unusually long lifetimes
In what interactions are strange particles produced?
in strong interactions
In what interactions are strange particles conserved?
in strong interactions
Through what interactions do strange particles decay?
through weak interactions
In what interactions is strangeness not always conserved?
in weak interactions
What is the range of the electromagnetic force?
Infinite
What is the carrier particle for the electromagnetic force?
(virtual) photons
How strong in the weak nuclear force compared to the electromagnetic force?
10^-11 times EM
What is the carrier particles for the weak nuclear force?
- W+
- W-
- (or Zo)
How strong in the strong nuclear force compared to the electromagnetic force?
100 times greater than EM
What are the carrier particles of the strong nuclear force?
Gluons (intranucleon)
Pions (internucleon)
Define electron capture
- When a proton in the nucleus captures an electron from the inner orbital
- It generates a neutron and a neutrino
What must be seen on all Feynman diagrams?
- all conservation laws apply at each junction
- paths diagonally to show movement through time
- bosons shown with a wiggly line
What are the axis of a Feynman diagram?
y-axis: time
x-axis: space
Give 4 roles of exchange/carrier particles
- transfer momentum
- transfer energy
- transfer force
- (sometimes) transfer charge
What is meant by an exchange/carrier particle?
- moves between one object/particle and another
- gives rise to the force between the particles
- transfer force, energy, momentum and sometimes charge
