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Chapter 1 Matter and radiation (1.1 (Structure of the atom (Relative= to…
Chapter 1
Matter and radiation
1.1
Structure of the atom
Positively charged nucleus (protons and neutrons) and negatively charged electrons surround the nucleus
Nucleon
- proton or neutron in the nucleus
Electrons held together by electrostatic force of attraction between electrons and nucleus
Relative
= to proton
Proton
Charge
- 1.60x-19C
Relative charge
- 1
Mass
-1.67x10-27
Relative mass
- 1
Neutron
Charge
- 0
Relative charge
- 0
Mass
- 1.67x10-27
Relative mass
- 1
Electron
Charge
- -1.60x10-19 C
Relative charge
- -1
Mass
- 9.11x-31kg
Relative mass
- 0.0005
Isotope
- same atomic number different number of neutrons
Nucleon number
- number of protons and neutrons
Nuclide
-type of nucleus with a certain number of protons and neutrons
Specific charge
- charge divided by mass
1.2
Strong nuclear force
Strong nuclear force
holds the nucleus together- overcomes electrostatic force of repulsion between protons in the nucleus
Range of 3-4 femtometres
Same effect between two protons as two neutrons
Attractive from 0.5fm to 3/4fm- repulsive force closer than 0.5 fm prevents protons and neutrons being pushed into each other
Radioactive decay
Alpha
Made up of alpha particles (2 protons, 2 neutrons)
Nucleus emits an alpha particle and forms a new nucleus
Beta
Fast moving electron
Neutron on nucleus turns into a proton and a Beta particle is created in nucleus and instantly emitted, an antineutrino is also emitted
Gamma
EM radiation emitted by an unstable nucleus
Can pass through thick metal plates
No mass or charge
Emitted by a nucleus with too much energy- followed by alpha or beta emission
1.3
EM Waves
Speed= 3.00x108 m/s
Wavelength
Radio- >0.1m
Microwave 0.1m-1mm
Infrared- 1mm-700nm
Visible- 700nm-400nm
UV- 400nm-1nm
X-Rays- 10nm-0.001nm
Gamma- <1nm
EM wave consists of an electric wave and magnetic wave that travel together and vibrate
at right angles to each other and to the direction they're travelling
In phase with each other
Red= electric field Blue= magnetic field
Photons
EM waves are emitted by a charged particle when it loses energy. Happens when
A fast-moving electron is stopped or slows down or changes direction
An electron in a shell of an atom move into a different shell of lower energy
Laser power
Consists of photons of the same frequency
Power of laser= energy per second transferred by the photons
Power= nhf
1.4
Antimatter
Antimatter+ matter-> destroy each other + radiation
Positron
- antiparticle of electron (+ve charge)
PET Scanners
use this effect
Positron emission
- Proton turns into a neutron in an unstable nucleus a neutrino is also emitted
Not natural- place stable isotope (l or s) into the path of a beam of protons- some of the nuclei absorb extra protons and become unstable proton-emitters
Every particle has an antiparticle that-
annihilates
the particle and itself if they meet - has the same rest mass - has opposite charge
Pair production
- photon with sufficient energy passing near a nucleus or an electron can change into a particle-antiparticle pair that then separate
E=mc2
Electron volts
- 1MeV=1.60x10-13 J
1eV= energy transferred when an electron in moved through a pd of 1V
Annihilation
- 2 photons produced so minimum energy= energy of 2photons (2hf) so
minimum energy of each photon= E0
Pair production
- photon creates a particle and anti-particle so
minimum energy of photon= 2E0
1.5
EM force
EM force between 2 charged particles is due to exchange of
Virtual particles
Virtual particles
- carrier of the EM force - a photon exchanged between two particles when they interact
Can represent it on a Feynman diagram
Weak nuclear force
Weak nuclear force
- force responsible for beta decay
In beta decay an electron or positron is created and a neutrino or anti-neutrino
Neutrino can interact with a neutron. Neutron-> proton
A β- (electron) is created and emitted
Anti-neutrino interacts with a proton. Proton-> Neutron
A β+ (positron) is created and emitted
W bosons
-exchange particles -non-zero mass -short range (0.001fm) -have charge
Beta decay
W- boson decays into a β- particle and an antineutrino
W+ boson decays into a β+ particle and a neutrino
Electron capture
Proton in a proton-rich nucleus can turn into neutron- due to interacting through weak interactions with an inner shell electron
Electron and proton collide at a high speed- proton can become a neutron- for an electron with sufficient energy the overall change could occur as a W- exchange from the electron to the proton
Force carriers
Photon and W boson= force carriers as they are exchanged when the EM force and weak forces act
