radiation

• ancient greeks thought atoms were small spheres that could not be divided
• JJ Thompson came up with plum pudding model that said that atoms were a ball of postive charge wit delocalised electrons
• Alpha scattering experiment was when alpha particles were fired at a thin sheet of gold
• In the alpha scattering , some of the particles bounced back suggesting an area of mass
• in the alpha scattering , some of the particles repelled showing that there was a positive charge
• in the alpha scattering , most of the particles went through suggesting the atom was mostly empty space
• neils bohr said that electrons orbit at fixed distances
• the neutron was discovered last by James Chadwick
• isotopes are atoms of the same element with different numbers of neutrons
• some isotopes have an unstable nucleus
• to become stable the nucleus gives out radiation
• radioactive decay is a very random process
• the activity is the rate at which unstable nuclei decay
• activity is measured in becquerels (Bq)
• to measure activity we use a Geiger-Muller tube
• the count rate is the number of decays per second recorded by a detector
• an alpha particle is a helium nucleus that has 2 protons and 2 neutrons
• a beta particle is an electron which is emitted when a nucleus decays into a proton and electron
• gamma rays are a type of electromagnetic radiation emitted from the nucleus
• neutrons are also a type of radiation
• alpha particles are strongly ionising
• beta particles are quite strongly ionising
• gamma is weakly ionising
• alpha particles ca be stopped by a sheet of paper
• beta can be stopped by a few mm of aluminium
• gamma has to be stopped by several cm of lead
• alpha only travels a short distance
• beta can travel about 15 cm
• gamma can travel several meters
• during alpha decay the mass number decreases by 4 and the atomic number decreases by 2
• in beta decay the atomic number increases by 1
• the half life is the time it takes for the number of nuclei to halve in the isotope
• half life can also be how long it takes for the count rate to halve from its initial level
• irradiation is exposing an object to nuclear radiation
• objects dont become radioactive after irradiation because they are not in contact with radioactive isotope
• ionising radiation can cause cancer
• alpha has low penetration power
• lead walls can prevent radiation from causing illness
• when unwanted isotopes end up on us this is contamination
• alpha particles can be stopped by dead cells on skin but are dangerous in the body