3.2 Particles And Radiation Flashcards
Speed of light
3 x 10^8 ms^-1
C =
Speed of light
Planck Constant
6.63 x 10^-34
H or h =
Planck constant
E =
Energy of photon (J)
n=
Number of photons emitted per second
1 electron volt =
1.6 x 10^-19 joules
Rest mass is…
…the mass of an object when it is not moving. It is measured in kg
m=
Mass
What state do electrons want to be in?
Ground state / level - so they want to lose any energy that they have
How can electrons move to higher energy levels?
Thermally, electrically, collision by particles and by absorbing radiation
What is ionisation?
When electrons are given enough energy to move beyond the energy levels and leave the atom. They must reach the ionisation energy level.
What is thermal excitation?
- where an atom gains thermal energy
- particles collide more, so electrons can move to increasingly higher energy levels
What is excitation by an electron (electrical excitation)?
- one electron collides with another in the atom
- energy from the colliding electron (e.g 10eV) will collide with the atomic electron, making it jump up an energy level (e.g 6eV), leaving the atomic electron with excess energy (e.g 4eV)
- if the colliding electron doesn’t have enough energy for the atomic electron to move up an energy level, it will just continue its way with the same amount of energy
What is electrical excitation like in a gas discharge tube?
Colliding electrons pass their energy on to any atoms in one movement, so there is a lot of excitement and de excitement, so the gas emits a lot of visible photons.
What happens when the particles in electrical excitation are alpha or beta?
- They have so much KE that they are likely to ionise the atomic electrons.
- this means there is no de-excitement of electrons so no photons are released.
What happens in excitation by absorption of radiation?
- when many photons from a source are incident on some atoms, some atomic electrons will absorb the photons’ energy.
- if this is the case, the atomic electron will jump up energy levels and the photon will disappear (will be absorbed) - but ONLY if the energy of the incident photon is exactly the same as the difference between any 2 energy levels in the atom.
What is fluorescence?
- when higher energy photons (usually ultra violet) are absorbed by atoms, electrons jump up multiple energy levels
- the electrons then de-excite, dropping through the different energy levels and emitting visible photons as they do so
What is the work function of a metal?
The minimum amount of energy that an electron needs to escape from the surface of an uncharted metal.
Every metal has a unique work function.
It is not the ionisation energy of these atoms as the electrons are already delocalised.
It is roughly 0.6eV for most metals
What is particle like behaviour?
- having and transferring kinetic energy + momentum
- affected by forces such as gravity + electrostatic
What is wave like behaviour?
Reflection, refraction, polarisation, diffraction, interference
P=
Particles momentum
What is a nucleon
A proton or neutron
Where is the proton/ atomic number found on periodic table
The bottom number (number of protons)
Where is the mass / nucleon number on the periodic table
Top number (number of protons and neutrons)
What are isotopes
Atoms of an element with different numbers of neutrons but the same number of protons
What is a nuclide
A type of nucleus (each element on the periodic table is a nuclide)
Specific charge of a particle =
Charge divided by mass
What is the strong nuclear force?
A force holding the nuclei in an isotope together, so that they don’t disintegrate - it overcomes the electrostatic force of repulsion between protons in the nucleus and holds them together with the neutrons.
Features of the strong nuclear force
- range of only 3-4 femtometers (fm); about the same as the diameter of a small nucleus
- has the same effect between two protons as it does between two neutrons or a proton and neutron
- acts as an attractive force from 3-4fm to 0.5fm, otherwise is a repulsive force.
What does an electromagnetic wave consist of?
An electric wave and a magnetic wave which travel together and vibrate:
- at right angles to each other and to the direction in which they are travelling
- in phase with each other (reach a peak together)
When are electromagnetic waves released?
By a charged particle when it loses energy. This can happen when:
- a fast moving electron is stopped or slows down or changes direction.
- an electron in a shell of an atom moves to a different shell of a lower energy
What is a photon?
Electromagnetic waves are released as short bursts of waves, each burst leaving the source in a different direction. Each burst is a packet of electromagnetic waves and is referred to as a photon
What is the photoelectric effect?
The emission of electrons from a metal surface when electromagnetic radiation is directed at the surface.
The radiation must be above a certain frequency (threshold frequency). Intensity of radiation is irrelevant
Power of a laser beam =
n (number of photons in the beam passing a point each second) x h x f
Electromagnetic repulsion diagram
Electron capture / electron- proton collisions diagram
Beta minus decay
Beta plus decay
What is the strong nuclear force?
- The force in an atom which overcomes the electrostatic force of repulsion between the protons in the nucleus
– its range is no more than about 3 to 4 femtometers (fm). 1fm = 10^-15m
– It is an attractive force from 3 to 4FM down to about nought. 5FM: at separation smaller than this it is a repulsive force that acts to prevent neutrons and protons being pushed into each other.
What are the three radiation types
- alpha: two protons + two neutrons
- beta: fast moving electron
- gamma: electromagnetic radiation emitted by an unstable nucleus
What is the equation for positron/ beta plus emission
Proton (p) -> neutron (n) + positron (e+) + neutrino (v)
Properties of a W boson exchange particle (which photons do not have)
- have a non-zero rest mass
- very short range of no more than about 0.001fm
- can be positively (W+) or negatively (W-) charged
- it is the exchange particle of the weak nuclear force, whereas a photon is the exchange particle of the electromagnetic force
What is the weak nuclear force referred to as
W boson
Describe a neutron - neutrino interaction
- a neutron interacts with a neutrino and changes into a proton
- an electron (beta minus particle) is created and emitted due to the change
Describe a proton - anti neutrino interaction
- a proton interacts with an antineutrino and changes into a neutron
- a positron ( beta plus particle) is created and emitted as a result of the change
Alpha particle properties
- charge of 2+
- mass of 4 units
What can kaons decay into
Pions, or a muon and antineutrino, or an antimuon and neutrino
What can a charged pion decay to
A muon and an antineutrino, or an antimuon and a neutrino
A zero charge pion decays into high energy photons
What can a muon decay into
An electron and antineutrino
An antimuon decays into a positron and a neutrino
What are the two types of hadron
- BARYON - can decay into protons
- MESON - hadrons that cannot decay into protons
Leptons vs hadrons
Leptons: interact through weak interaction, gravitational interaction and electromagnetic interaction (if charged)
Hadrons: can act through all four fundamental forces: the strong force, the weak force (most common), the electromagnetic force (if charged) and the gravitational force.
Photoelectric effect explanation
– 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, which is equal to the energy of a light photon
– An electron can leave the metal surface of the energy gained from the single photon exceeds the work function of the metal
This is the minimum energy needed by an electron to escape from the metal surface
Excess energy gained by the photoelectron press comes kinetic energy
What is one electron volt equal to
The work done when an electron is moved to a potential difference of 1 V
Describe excitation
– When excitation occurs the colliding electron makes an electron inside the atom move from an inner shout to an outer shell
– energy is needed for this process because the atomic electron moves away from the nucleus of atoms
– the excitation energy is always less than the ionisation energy of the atom because the atomic electron is not removed completely from the atom when excitation occurs
What is the difference between ionisation and excitation
Ionisation occurs when an electron is removed or added to the atom where is excitation is just the movement of an electron from one shell to another
Which particles have strangeness
Rules of strange particles
- Are produced through the strong interaction
- Decay through the weak interaction
- Are produced in quark-antiquark pairs
What does a shell diagram represent
The atom’s electrons drawn in the lowest possible configuration of energy levels. It does not show any higher energy levels that may exist
