Particles and Radiation Flashcards
Charge of a proton
+ 1.6 x 10^-19 C
Charge of an electron
- 1.6 x 10^-19 C
Proton rest mass
1.673 x 10^-27 kg
Neutron rest mass
1.675 x 10^-27 kg
Electron rest mass
9.11 x 10^-31 kg
Specific charge
Charge / mass
Isotopes
Atoms with the same number of protons and different numbers of neutrons.
Proton number / Atomic number / Z
Number of protons in the atom.
Nucleon number / Mass number / A
Total number of protons and neutrons in an atom.
Strong Nuclear Force
Acts between nucleons. Attractive between 3-4 fm and 0.5 fm. Repulsive for distances smaller than 0.5 fm.
Alpha radiation
Consists of alpha particles which are comprised of two protons and two neutrons. Highly ionising, can be stopped by paper.
Beta radiation
Consists of fast moving electrons. Stopped by aluminium.
Gamma radiation
Electromagnetic radiation emitted by an unstable nucleus. Has no mass or charge and can pass through thick metal plates but is stopped by lead. Emitted by a nucleus with too much energy, following an alpha or beta emission.
Beta minus decay
A neutron in the nucleus changes into a proton, a beta particle is created in the nucleus and is emitted along with an antineutrino.
Wave speed equation
𝑐 =𝑓 𝜆
Wavelength range of radio waves
Larger than 0.1 m
Wavelength range of microwaves
1 mm to 0.1 m
Wavelength range of infrared
700 nm to 1 mm
Wavelength range of visible light
400 nm to 700 nm
Wavelength range of ultraviolet
1 nm to 400 nm
Wavelength range of X-rays
0.001 nm to 10 nm
Wavelength range of gamma rays
Less than 1 nm
Electromagnetic waves
Emitted by a charged particle when it loses energy for example when a fast moving electron is stopped, slows down or changes direction or when an electron in a shell of an atom moves to a different shell of lower energy. Consists of an electric wave and a magnetic wave which travel together in phase at right angles to eachother and the direction they are travelling.
Photons
Packets of electromagnetic waves.
Photon energy equation
E = h f
Planck’s constant, h
6.63 x 10^-34 Js
Power of a laser beam
n h f, where n is the number of photons in the beam passing a fixed point per second.
Antiparticles
There is a corresponding antiparticle for every type of particle that annihilates the particle if they meet, converting their total mass into photons and has exactly the same rest mass and opposite charge to the corresponding particle.
Electron volt
The energy transferred when an electron is accelerated through a potential difference of 1 volt.
Annihilation
Occurs when a particle and a corresponding antiparticle meet and their mass is converted into radiation energy. Two gamma ray photons are produced in this process.
Pair production
Occurs when a photon with sufficient energy passing near a nucleus or an electron suddenly changes into a particle-antiparticle pair and vanishes. Only gamma ray photons have enough energy for pair production.
Exchange particles for the electromagnetic force
Virtual photons.
Exchange particles for the weak nuclear force
W bosons.
W bosons
Have a non-zero rest mass, have a very short range of no more than about 0.001 fm and are positively charged or negatively charged.
Weak Nuclear Force
Acts on all types of particles.
Examples of the weak interaction
Beta minus decay, beta plus decay, electron capture, neutrino interacting with a neutron and making it change into a proton with a beta minus particle being created and emitted and an antineutrino interacting with a proton making it change into a neutron with a beta plus particle being created and emitted.
Beta plus decay
A proton in the nucleus changes into a neutron, beta plus particle and neutrino are emitted, W+ exchange particle.
Electron capture
Occurs when a proton in a proton-rich nucleus turns into a neutron as a result of interacting through the weak interaction with an inner-shell electron from outside the nucleus. The W+ boson changes the electron into a neutrino. Can also happen when a proton and an electron collide at very high speeds.
Exchange particles for the strong nuclear force
Gluons
Strong nuclear force
Affects hadrons only, has a range of between 0.5 fm and 3 fm. Repulsive for distances below 0.5 fm.
Muons, μ
Heavy electron with a rest mass of over 200 times the rest mass of the electron. Negatively charged, decays into an electron and an antineutrino.
Pion or π meson
A particle which can be positively charged, negatively charged or neutral and has a rest mass greater than a muon but less than a proton. Charged pions can decay into a muon and an antineutrino or an antimuon and a neutrino. A neutral pion decays into high-energy photons.
Kaon or K meson
Can be positively charged, negatively charged or neutral. Has a rest mass greater than a pion but still less than a proton. Can decay into pions or a muon and an antineutrino or an antimuon and a neutrino.
Hadrons
Particles and antiparticles that can interact through all four fundamental interactions (e.g. protons, neutrons, π mesons and K mesons). Interact through the strong interaction and electromagnetc interaction if charged. Apart from the proton, which is stable, hadrons tend to decay through the weak interaction.
Leptons
Particles and antiparticles that interact through the weak interaction, gravitational interaction and the electromagnetic interaction (if charged). (e.g. electrons, muons, neutrinos).
Baryons
Protons and all other hadrons (including neutrons) that decay into protons, either directly or indirectly.
Mesons
Hadrons that do not include protons in their decay products. In other words, kaons and pions are not baryons. Consisting of a quark and antiquark pair.
Charge of an up quark
+ 2/3
Charge of a down quark
- 1/3
Charge of a strange quark
- 1/3
Charge of an anti up quark
- 2/3
Charge of an anti down quark
+ 1/3
Charge of an anti strange quark
+ 1/3
Strangeness of an up quark
0
Strangeness of a down quark
0
Strangeness of a strange quark
-1
Lepton number of a lepton
+ 1
Lepton number of an antilepton
- 1
Strangeness of an anti up quark
0
Strangeness of an anti down quark
0
Strangeness of an anti strange quark
+ 1
Baryon number of an up quark
+ 1/3
Baryon number of a down quark
+ 1/3
Baryon number of a strange quark
+ 1/3
Baryon number of an anti up quark
- 1/3
Baryon number of an anti down quark
- 1/3
Baryon number of an anti strange quark
- 1/3
Quark composition of a proton
uud
Quark composition of a neutron
udd
Only stable baryon
Proton
Lepton number
Conserved in all interactions
Strangeness
Conserved in all strong interactions
Baryon number
Conserved in any interaction
Baryon number of a baryon
+ 1
Baryon number of an antibaryon
- 1
Lepton number of a muon
+ 1
Lepton number of an antimuon
- 1
Lepton number of an electron
+ 1
Lepton number of a positron
- 1
Lepton number of an electron neutrino
+ 1
Lepton number of a muon antineutrino
- 1
The photoelectric effect
When electrons are emitted from the surface of a metal when electromagnetic radiation above a threshold frequency was directed at the metal.
Threshold frequency
The minimum frequency of the incident electromagnetic radiation for which photoelectric emission of electrons from a metal takes place. Is a material property, varies depending on the type of metal.
Number of photoelectrons emitted per second
Proportional to intensity of incident radiation only if the frequency is greater than the threshold frequency. Below the threshold frequency, no photoelectric emission takes place, no matter the intensity of the incident radiation.
Energy of a photon
E = hf
Why wave theory couldn’t explain the photoelectric effect
Wave theory of light could not explain the threshold frequency as according to wave theory, each electron on the surface of the metal should gain some energy from the incoming waves regardless of how many waves arrive each second.
Einstein’s explanation of the photoelectric effect
Einstein proposed the photon theory of light in 1905 to explain the photoelectric effect. He assumed that light is composed of wave packets (photons). When light is incident on a metal surface, an electron at the surface absorbs a single photon from the incident light and therefore gains energy equal to hf.
Planck’s constant, h
6.63 x 10^-34 Js
Work function, ϕ
The minimum energy needed by an electron to escape from the metal surface, Excess energy gained by photoelectrons becomes its kinetic energy.
Maximum kinetic enegy of a photoelectron
Ek max = hf - ϕ
Stopping potential, Vs
The potential needed to stop the fastest moving electrons.
Stopping potential, Vs equation
e Vs = Ek max
Vacuum photocell
A glass tube that contains a metal plate, referred to as the photocathode, and an anode. When light of a frquency greater than the threshold frequency for the metal is directed at the photocathode, electrons are emitted from the cathode and are attracted to the anode. The microammeter in the circuit can be used to measure the photoelectric current. This is proportional to the number of electrons per second that transfer from the cathode to the anode.
Ion
A charged atom, the number of electrons in an ion is not equal to the number of protons. Formed from an uncharged atom by adding or removing electrons from the atom, adding electrons makes the atom into a negative ion and removing electrons makes the atom into a positive ion.
Ionisation
Any process of creating ions. Radiation create ions when they pass through substances and collide with the atoms of the substance. Electrons passing though a fluorescent tube create ions when they collide with the atoms of the gas or vapour in the tube.
The electron volt
A unit of energy equal to the work done when an electron is moved through a pd of 1 V.
Excitation
Electrons gain enough energy to move to higher energy levels or from an inner shell to an outer shell of an atom.
Excitation energies
The energy values at which an atom absorbs energy.
Ground state
The lowest energy level.
De-excitation
The process by which an atom moves to a lower energy level. Excited electron leaves a vacancy in shell from which it moved, the vacancy is filled by an electron from an outer shell and it emits a photon. The energy of the photon is equal to the energy lost by the electron.
Excitation using photons
An electron can absorb a photon and move to an outer shell with a vacancy but only if the energy of the photon is equal to the gain in the electron’s energy.
When is strangeness conserved?
During strong and electromagnetic interactions but not during weak interactions.
The particles that are produced when a muon decays
Electron, electron antineutrino and muon neutrino.
