Y1: Particles and radiation Flashcards
What is the charge of a proton
+1.6x10^-19 C
What is the charge of a neutron
0 C
What is the charge of an electron
-1.6x10^-19 C
What is the rest mass of a proton
1.67(3)x10^-27 kg
What is the rest mass of a neutron
1.67(5)x10^-27 kg
What is the rest mass of an electron
9.11x10^-31 kg
What is the Proton number (atomic number) of an atom
Z: The number of protons in the nucleus
- Defines the element
- In a neutral atom Z=No. of electrons
(bottom number)
What is the Nucleon number (mass number) of an atom
A: The number of protons and neutron in the nucleus
- As the mass of an electron≈0, A≈RAM of the atom
What is specific charge (Ckg^-1)
Ratio of a particle’s charge to it’s mass
(Charge/mass)
What are isotopes
Atoms with the same number of protons but different number of neutrons
How does being an isotope effect the stability of an atom
The greater the number of neutrons compared to the protons, the more unstable the nucleus, so it may be radioactive and decay
What is isotopic data
The relative amounts of different isotopes of an element present in a substance
What forces act within the nucleus of an atom
- Electromagnetic force: causes the positive protons to repel each other
- Gravitational force: Causes the nucleons to be attracted to each other due to their mass
(EM force»_space; G force) - Strong nuclear force: holds the nucleus together
How does the strong nuclear force vary with respect to distance
- Repulsive for separation < 0.5fm
- Attractive force increases past 0.5fm, up to ~3fm, after which the attraction approaches 0
What is nuclear decay
When unstable nuclei emit particles to become more stable
What is alpha decay
When an α-particle is emitted from the nucleus (2 proton and 2 neutrons, ∴ α-particle = helium atom)
- α-particle has a short range of a few cm in air
- Only occurs in very large atoms, Z>82, as the strong nuclear force can’t keep them stable)
What is beta-minus decay
- The emission of an electron and an antineutrino
- When a β- particle is ejected, one neutron changes into a proton (∴ occurs when isotopes are neutron rich)
- The antineutrino particle released carries some energy and momentum to conserve the properties during the interaction
- β- particles can travel several meters through air
What is a photon
A ‘discrete packet’ of energy all EM waves exist as (ie. light)
How do you calculate the energy of a photon
Energy of one photon (J) = Freq. (Hz) x Planck’s Constant (Js)
E = hf
∴ E = hc/λ
What is Planck’s constant
h = 6.63x10^-34 Js
What is an antiparticle
Each particle has a corresponding antiparticle with the same mass, but opposite charge
What is the antiparticle of a proton
Antiproton
- Charge = -1.6x10^-19 C
- Mass = 1.67(3)x10^-27 kg
What is the antiparticle for a neutron
Antineutron
- Charge = 0 C
- Mass = 1.67(5)x10^-27 kg
What is the antiparticle for an electron
Positron
- Charge = 1.6x10^-19 C
- Mass = 9.11x10^-31 kg
What is the antiparticle for a neutrino
Antineutrino
- Charge = 0 C
- Mass = 0 C
What is pair production
When energy is converted into mass, giving an equal amount of matter and antimatter
eg. If a photon has enough energy, it can produce an electron-positron pair (as electrons have a low mass)
What is the relationship between energy and the mass it can produce
E = mc^2
What is the rest energy of a particle (Eo)
The amount of energy that would be produced if all the mass was converted into energy
What is the minimum amount of energy required for pair production
The total rest energy of the two particles produced
∴ E(min) = 2Eo
What is Annihilation
When a particle and antiparticle meet, all of their mass is converted into energy, producing 2 gamma ray photons
What is the minimum energy of a photon produced during annihilation
The 2 photons have a total minimum energy equal to the total rest energy of the two particles
∴ E(min) = Eo
What are the two fundamental classes of subatomic particles
Bosons (Mesons and ‘photons/W-bosons/etc…’)
Fermions (Baryons and Leptons)
What are hadrons
Particles made up of quarks, that feel the strong nuclear force
What are the two types of hadrons
- Baryons (3 quarks)
- Mesons (2 quarks)
What are baryons
Hadrons made up of 3 quarks (eg. nucleons)
- All will eventually decay into a proton
- Antibaryons are the antimatter of baryons, but don’t exist in ordinary matter as they are annihilated
What is the baryon number (B)
A quantum number that must be conserved
- All baryons: B = +1
- All antibaryons: B = -1
- All other particles (not baryons): B = 0
What are mesons
Hadrons made up of quark-antiquark pair
- All will eventually decay into pions
- Interact with baryons via the strong force
- Lots are produced in high energy particle collisions
(eg. detected in cosmic ray showers)
What are pions (π-mesons)
- The lightest mesons
- Exchange particles for the strong nuclear force
- Different versions with different charges
(π+, π°, π-)
π- = anti π+
What are kaons (K-mesons)
- Heavier and more unstable than pions
- Have short lifetime and decay into pions
- Different versions with different charges
(k+, k°, k-)
k- = anti k+
What are Leptons
Fundamental particles that don’t feel the strong nuclear force, so interact via the weak interaction
What are the different flavours of leptons
- Electron (e-): Stable leptons
- Muons (μ-): Heavier and will eventually decay into electrons
+ Tau (T): Largest lepton - Not required for AQA spec.
What is the Lepton number
A quantum number that must be conserved, counted separately for different types of leptons
- Le = Electron number
- Lμ = Muon number
What is a neutrino (V)
- A neutral particle With a mass ≈ 0
- Conserves properties during the weak interaction
- Different flavours for different leptons (Ve, Vμ, etc.)
What are strange particles
Particles that have a property called strangeness
- Created via the strong interaction
- Strangeness must be conserved, so strange particles are always created in pairs
- Decays via the weak interaction (although strangeness isn’t conserved during this)
What properties need to be conserved during different interactions
- Charge (all particle interactions)
- Baryon number (all particle interactions)
- Lepton number (all particle interactions, electrons/muons separately)
- Strangeness (Only strong interaction, and some weak interactions)
(+ momentum)
What are quarks
Fundamental particles that make up hadrons.
- Different flavour quarks have different properties, so determine the properties of the hadron they are contained within
- Each has a corresponding antiquark with the opposite properties
What is the relative charge of an up quark (u)
+ 2/3
What is the baryon number of an up quark (u)
+ 1/3
What is the strangeness of an up quark (u)
0
What is the relative charge of a down quark (d)
-1/3
What is the baryon number of a down quark (d)
+ 1/3
What is the strangeness of a down quark (d)
0
What is the relative charge of a strange quark (s)
-1/3
What is the baryon number of a strange quark (s)
+ 1/3
What is the strangeness of a strange quark (s)
-1
What is the quark composition of a baryon
Contains 3 quarks (antibaryons have 3 antiquarks), with the total of the quark properties giving the properties of the baryon
What is the quark composition of a proton
uud
What is the quark composition of a neutron
udd
What is the quark composition of a meson
Contains 1 quark and 1 antiquark, with the total of the quark properties giving the properties of the meson
What is the quark composition and properties of a π+ meson
ud̅
C = +1
S = 0
What is the quark composition and properties of a π° meson
uu̅ or dd̅
C = 0
S = 0
What is the quark composition and properties of a π̅° meson
uu̅ or dd̅
C = 0
S = 0
What is the quark composition and properties of a π- meson
du̅
C = -1
S = 0
What is the quark composition and properties of a k+ meson
us̅
C = +1
S = +1
What is the quark composition and properties of a k° meson
ds̅
C = 0
S = +1
What is the quark composition and properties of a k̅° meson
sd̅
C = 0
S = -1
What is the quark composition and properties of a k- meson
su̅
C = -1
S = -1
What is meant by quark confinement
The inability of a quark to exist by itself
- eg. If energy is directed at a proton, 1 quark won’t be removed/left alone, but the energy would turn into a quark-antiquark pair, leaving the proton as it is
What is the weak interaction
A particle interaction where one quark turns into another
eg. beta +/- decay
What is a virtual particle (gauge boson)
An exchange particle that only exists for a short time, allowing for a particle interaction to occur
(different types for different fundamental forces)
What are the 4 fundamental forces, and what are their gauge bosons
- Strong nuclear force: Pions (π+, π°, π-) - Affects Hadrons
- Weak force: W bosons (+/-) - Affects all particles
- Electromagnetic force: Virtual photons (𝛾) - Affects Charged particles
+ Gravitational force: Thought to be gravitons, but has never been directly observed - Affects all particles
How does the size of an exchange particle effect it’s range (and therefore the range of the force)
The larger the mass, the shorter the range, as a large mass requires a large amount of energy to be created
- A W-boson has a mass 100x greater than a proton, so the weak interaction has a much smaller range than the strong force
- A photon has zero mass, so the EM force has an infinite range
What is a Feynman diagram and what does it show
Particle interaction diagrams that show the exchange of a particle
- y-axis = time (bottom is the start)
- x-axis = displacement
- Baryons stay on the left, leptons stay on the right (if both are present)
What happens during beta-minus decay
n → p + e- + V̅e
- A neutron is turned into a proton (down quark to an up quark)
- W- Boson transfers a negative charge to balance the charges
What happens during beta-plus decay
p → n + e+ + Ve
- A proton is turned into a neutron (up quark to an down quark)
- W+ Boson transfers a positive charge to balance the charges
What happens during electron capture
p + e- → n + Ve
- A proton ‘captures’ an electron to become a neutron
- Proton acting on an electron
∴ W+ boson is transferred from the proton to the electron, to conserve charge
What happens during an electron-proton collision
p + e- → n + Ve
- A high speed electron collides with a proton, turning it into a neutron
- Electron acting on a proton
∴ W- boson is transferred from the electron to the proton, to conserve charge
how do particles interact during electromagnetic repulsion
- When particles with the same charge get close, they repel each other
- A virtual photon is exchanged
