Atom consists of +vely charged nucleus (made of protons and neutrons), surrounded by -ve electrons
Electrons are held in the atom by the electrostatic force of attraction between them and +ve nucleus.
Isotopes are atoms of an element with the same number of protons, different number of neutrons.
Proton Number=Z=atomic number
Nucleon Number=A=mass number
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1.1 Inside the Atom (cont)
Specific charge is defined as charge of a charged particle divided by its mass
Units are C/kg
All masses needed are given to you, always use +/- 1.6x10^-19 for the charge of any particle for each increment of charge.
Specific charge of a nucleus includes all protons and neutrons, and the charge of the protons.
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1.2 Stable and Unstable Nuclei
Strong nuclear force is the force that overcomes electrostatic repulsion between protons in the nucleus, and (except for unstable nuclei) holds protons and neutrons together.
Strong force has a range of 3-4 femtometers (x1-^-15), which is diameter of small nucleus.
S.F acts on all protons and neutrons equally, depending on their distance from the centre of the nucleus.
It is an attractive force from 0.5fm-3/4fm. Before 0.5fm strong force becomes a repulsive force to stop neutrons/protons colliding.
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1.2 Stable and Unstable Nuclei (cont)
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1.2 Stable and Unstable Nuclei (cont)
In Alpha radiation, an unstable nucleus emits an alpha particle (2 protons, 2 neutrons), forming an new nucleus with proton number -2, nucleon number -4.
Beta radiation consists of fast-moving electrons. In beta radiation (Beta + decay) a neutron in the unstable nucleus changes into a proton. A Beta + particle is instantly emitted along with an antineutrino.
Gamma radiation is electromagnetic radiation emitted by unstable nuclei.
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1.2 Stable and Unstable Nuclei (cont)
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1.2 Stable and Unstable Nuclei (cont)
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1.3 Photons
In a vacuum, all electromagnetic waves travel at the speed of light, c.
speed of EM wave = frequency / wavelength
An electromagnetic wave consists of an electric wave and a magnetic wave which travel together and vibrate perpendicular to eachother and the direction which they're traveling.
They are in phase.
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1.3 Photons (cont)
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1.3 Photons (cont)
A photon is a packet of electromagnetic waves, with a fixed energy amount. This photon energy = h x f.
A laser beam emits coheret and monochromatic light. So, all photons emitted have the same frequency and energy.
The power of a laser will be the total amount of energy emitted per second, = n x h x f, where n= number of emitted photons per second.
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1.4 Particles and Antiparticles
An antiparticle has exactly the same mass and the opposite charge to its corresponding particle.
When a particle and its corresponding antiparticle collide, they annihilate eachother, converting their total mass (energy) into 2 photons.
The minimum energy of both photons produced is the rest masses (energies) of the particle/antiparticle pair. So, minimum energy of 1 emitted photon is rest mass of 1 particle or antiparticle.
Any extra energy is converted into kinetic energy.
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1.4 Particles and Antiparticles (cont)
Pair production is when a photon creates a particle and a corresponding antiparticle, and vanishes in the process.
A photon must have a minimum energy (hf) that is enough to create both the particle and the antiparticle at rest. hf=2E.
Any extra energy is given to the particle and antiparticle creates for kinetic energy.
For calculations always use Joules. 1eV = 1x10^-19 J
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1.4 Particles and Antiparticles (cont)
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1.5 How Particles Interact
When a single force acts on an object, it changes the momentum of the object.
When two particles interact, they exert equal and opposite forces on eachother. Momentum is transferred between these two particles.
Exchange particles make this particle interaction possible by creating and exchanging a force between 2 particles.
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1.5 How Particles Interact (cont)
The strong nuclear force holds the neutrons and protons in a nucleus together.
There must be another force that causes particle decay and certain particle interactions. This is the weak nuclear force.
Weak nuclear force is weaker than the strong nuclear force so that it does not affect stable nuclei.
In most weak interactions, the exchange particles present are W bosons. They have a non-zero rest mass, have a very short range and are charged.
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