P6 - Radioactivity
Structure of an Atom
Electron
Negatively Charged
Relative Mass of 1/1836
Orbits the Nucleus on Electron Shells
Neutron
Proton
No Charge
Relative Mass of 1
Positively Charged
Relative Mass of 1
Found in the Nucleus
Found in the Nucleus
Atomic Symbols
Symbol
Proton Number
Mass Number
Number of Protons + Number of Neutrons
e.g. He, O, Na, Zn
Number of Protons
Isotopes
Radioactivity
An isotope is an atom with a different number of neutrons
A change in the number of neutrons causes the mass number to increase or decrease
A radioisotope is simply an isotope that is radioactive
e.g. carbon 14, which is used in carbon dating
The isotopes of many atoms which are unstable and have extra energy are called radioisotopes.
Radioisotopes emit the extra energy as radiation, to become more stable, by splitting up
Types of Radiation
Alpha
An atom decays into a new atom and emits an alpha particle
Has 2 protons and 2 neutrons
Beta
Gamma
An atom decays into a new atom by changing a neutron into a proton and electron
The fast moving, high energy electron is the beta particle
after alpha or beta decay surplus energy is emitted called gamma radiation
gamma radiation has a very high frequency with short wavelength
The atom is not changed
Half life
Stopped by a sheet of paper
Stopped by a few mm of aluminium
Stopped by a few cm of lead
This is how long it takes half the radioisotope in a sample to decay
To find the half life on a graph, find the amount of half the sample, go across horizontally till the curved line, go down to the axis then you know the half life
Ionisation
Ionising radiation is when radiation collides with neutral atoms or molecules it alters their structure by knocking off electrons leaving behind ions.