P6- Radioactive materials

P6- Radioactive materials

1. Using ionising radiation

   • Sterilising food- Microbes are killed which keeps the food fresh for longer, without having to freeze it or cook it. The food is not radioactive afterwards so it's safe to eat
   • Sterilising medical equipment- Microbes are killed. This is better than boiling plastic instruments, which might be damaged by high temperatures. You need to use a strongly radioactive source that has a long half-life, so that it doesn't need replaced often
   • Detecting diseases using tracers- Tracers are radioactive molecules that can be injected into people. Their progress around the body us followed using an external detector. They can detect cancer or whether and organ is working properly. Isotopes used as tracers must be gamma or beta so the radiation passes out of the body. They have a short half-life so that the radioactivity inside the patient quickly disappears
   • Treating cancer- Since high dosed of gamma rays will kill all living cells, they can be used to treat cancers. The rays have to be directed carefully and at just the right dosage so as to kill the cancer cells, without damaging too many normal cells

2. Danger from radiation

   • Irradiation- being exposed to radiation without coming into contact with the source. The damage to your body stops as soon as you leave the radioactive area
   • Contamination- picking up some radioactive material e.g. by breathing it in. You'll still be exposed to the radiation once you've left the radioactive area

3. Nuclear fission

   • Dealign with waste
     • 'Low level' waste e.g. paper and gloves can be disposed of by burying it in secure landfill sites
     • 'Intermediate level' waste includes things like the metal cases of used fuel rods or hospital waste. It's often sealed in concrete blocks and put in steel canisters for storage
     • 'High level' waste is stored in glass and steel, then cooled for 50 years before it's moved to permanent storage
       • The canisters could then be buried deep underground however it's difficult to find suitable places e.g. places that do not suffer earthquakes
   • Controlling nuclear fission
     • Fuel rods- Where the fuel used in nuclear reactors is kept
     • Control rods- absorb some of the neutrons and slow down the reaction
     • Coolant e.g. water- is used to take away the heat produced by the fission process
   • A nuclear fuel e.g. uranium or plutonium, releases large amounts of energy when its nuclei split apart. Neutrons are fired at the fuel, causing some of its large, unstable nuclei to split into two small nuclei. Each split nucleus also releases 2 or 3 more neutrons and lots of energy. This is how the chain reaction starts.

4. The Atom and Nuclear fusion

   • Two nuclei can combine to create a larger nucleus, releasing energy when they do. For example hydrogen nuclei fuse together to make helium nuclei. Nuclei can only fuse if they overcome the repulsive electrostatic force and get close enough for the strong force to hold them together. That means you need a high temperature to be able to fuse nuclei together
   • Rutherford's scattering showed that atoms have a positive nucleus. He tried firing alpha particles- which are positively charged at thin gold foil. Most of the alpha particles went straight through but a few came straight back. The nucleus had to have a positive charge otherwise the positively charged alpha particles wouldn't be repelled

5. Radioactivity

   • Radioactive elements emit ionising radiation
   • The number of neutrons in an element isn't fixed. Many elements have a few different isotopes- atoms with the same number of photons but a different number of neutrons
   • Some isotopes are radioactive- the nucleus is unstable, so it decays and emits radiation. Carbon-14 is an unstable isotope of carbon whereas carbon-2 is a stable isotope

6. Alpha, Beta and Gamma

   • Alpha
     • Alpha particles are relatively big and heavy and fairly slow-moving
     • They don't penetrate far and are blocked by paper
     • An alpha particle is a helium nucleus with a mass of 4 and a charge of +2
   • Beta
     • Blocked by thin aluminium
     • They move quite fast and are small
     • They penetrate moderately into materials before they're stopped
     • A beta particle is identical to an electron, with virtually no mass and a charge of -1
     • During beta decay, a neutron in the nucleus turns into a proton
   • Gamma
     • A type of electromagnetic wave which has no mass
     • They can penetrate a long way into materials without being stopped
     • Blocked by thick lead