Radioactivity

• each element was made up of a different types of 'atom'
• JJ Thompson discovered that electrons could be removed from atoms
• he suggested that atoms were like spheres of positive charge with tiny negative electrons stuck in them like plums in plum pudding
• in 1909 Rutherford and Marsden tried firing a beam of alpha particles at thin gold foil
• most of the alpha particles went straight though but some came straight back at them
• most of the mass of the atom was concentrated at the centre of the nucleus and it would have has a positive charge to repel the alpha particles
• the nucleus contains protons and neutrons
• atoms have no charge
• if electrons are added or removed, the atom becomes are charged ion

• isotopes are atoms with the same number of protons but a different number of neutrons
• they have the same atomic number but a different mass number
• atomic number if the number of protons in an atom
• mass number is the number of protons plus neutrons
• isotopes tend to be radioactive which means they decay into other elements and give out radiation
• this process is completely random
• it's completely unaffected by physical conditions like temperature of chemical bonding
• radioactive substances spit out one or more of the three types of radiation: alpha, beta or gamma
• radioactivity of natural unstable isotopes are happening all around us (air, food or building materials)
• radiation from space is known as cosmic rays from the sun
• radiation due to man made sources eg, nuclear weapon tests or accidents

ALPHA:

• an alpha particle is two neutrons and two protons which is the same as a helium nucleus
• they are relatively big, heavy and slow moving
• they therefore don't penetrate very far into materials and are stopped quickly even in air
• they are strongly ionising which means they bash into a lot of atoms and knock electrons off them before they slow down which creates lots of ions
• stopped by paper
  BETA:
• they move quite quick and they are small
• they penetrate moderately into materials before colliding, have a long range in the air and are moderately ionising too
• for every B particle emitted, a neutron turns to a proton in the nucleus
• a B particle is an electron
• stopped by aluminium
  GAMMA:
• they are the opposite of alpha particles
• they penetrate far into materials without being stopped and pass though air
• they are weakly ionising becuase they pass though rather than collide
• gamma rays have no mass or charge
• stopped by lead

• radiation dose depends on the type and amount of radiation you're exposed to
• the higher the radiation dose, the more at risk you are of developing cancer
• certain underground rocks can cause higher levels at the surface, especially if they release radioactive radon gas
• nuclear industry workers are exposed to 10 times the normal amount of radiation
• radiographers work in hospitals using ionising radiation so have a higher risk of radiation exposure
• at high altitudes the background radiation increases due to exposure to cosmic rays
• alpha particles have a positive charge and beta particles are negatively charged
• when travelling though a magnetic field both alpha and particles will be deflected
• they're deflected in different directions due to their charge

• each time a decay happens and radiation is given out, it means that one more radioactive nucleus has disappeared
• as the unstable nuclei all disappear, the activity will decrease
• the older a sample becomes, the less radiation it will emit
• the problems with trying to measure the time it take is that the activity never reaches zero which is why the idea of half life is used to messer how quickly the activity drops off
• half life is the average time it takes for the number of nuclei in a radioactive isotope sample to half
• short life means the activity falls quickly becuase it decays quickly
• long half life means the activity falls slowly becuase most of the nuclei don't decay for a long time

SMOKE DETECTORS:

• a weak source of alpha is placed in the detector
• the source causes ionisation and a current flows between the electrodes
• if there's a fire, the smoke will absorb the radiation so the current will stop and the alarm sounds
  TRACERS IN MEDICINE:
• certain isotopes can be injected into people can can be tracked using an external detector
• iodine 131 is absorbed by the thyroid gland and emits radiation
• must be gamma or beta radiation so they can pass out of the body
  RADIOTHERAPY:
• gamma rays can be used to treat cancers
• the rays have to be directed carefully and just the right dosage so they don't kill do many normal cells
• some damage is done to normal cells and can make the patient very ill
  STERILISATION:
• the gamma rays can kill microbes which keeps food fresh for longer and sterilise medical instruments
• the isotopes used for this are very strong emitter of gamma rays with a reasonably long half life

• alpha, beta and gamma radiation can enter living cells and collide with molecules
• this causes ionisation whuch can damage or destroy molecules
• the extent of the harmful effects depends on 2 things: how much exposure to radiation and the energy and penetration of the radiation
• beta and gamma can enter the delicate organs whereas alpha can't get though the skin
• alpha is very dangerous inside the body but gamma and beta don't cause as much damage
• use radioactive sources for as little time as possible to reduce exposure
• never allow skin contact
• keep the source away from the body