Atomic Structure

Atomic Structure

1. developing the model of the atom

   • John Dalton - start of 19th century - atoms were first described as solid spheres
     • JJ Thompson - 1897 - Thompson suggested the plum pudding model - the atom is a ball of charge with electrons scattered in it
       • Ernest Rutherford - 1909 - Alpha Scattering experiment - Rutherford discovered that the mass is concentrated at the centre and the nucleus is charged. Most of the mass is in the nucleus. Most atoms are empty space
         • Niels Bohr - ~1911 - Bohr theorised that the electrons were in shells orbiting the nucleus
           • James Chadwick - ~1940 - Chadwick discovered neutrons in the nucleus

2. isotopes

   • an isotope is an element with the same number of protons but a different number of neutrons. They have the same atomic number, but different mass numbers.
     • some isotopes are unstable and, as a result, decay and give out radiation.
       • Ionising radiation is radiation that can knock electrons off atoms
         • Just how ionising this radiation is, depends on how readily it can do that.

3. alpha

   • beta
     • gamma
       • a gamma wave is a wave of radiation and is the most penetrating - stopped by thick lead and concrete
     • beta radiation is a fast moving electron that can be stopped by a piece of aluminium. Beta radiation is emitted by an atom when a neutron splits into a proton and an electron
   • alpha radiation is an alpha particle emitted from the nucleus of a radioactive nuclei. It is made from two protons and two neutrons. They can't travel too far in the air and are the least penetrating - stopped by skin and paper. However, they are highly ionising because of their size.

4. half life

   • different half-lives of radioactive isotopes
     • all radioactive isotopes have different half-lives
       • some are very short and others are much longer
         • The uses of these will depend on the half-life
           • for example, you would use an isotope with a short half-life as a medical tracer so it is not in the body for too long
   • the half-life is the time taken for the number of radioactive nuclei in an isotope to halve
     • radioactivity is a random process - you will not know which nuclei will decay
       • radioactive decay is measured in becquerels Bq. 1 Bq is one decay per second
         • radioactive substances give out radiation from their nucleus
     • a graph of half-life can be used to calculate the half-life of a material and will always have this shape:
       • judging from the graph, the radioactive material has a half-life of two days

5. irradiation

   • irradiation occurs when materials are near a radioactive source.
     • The source is sometimes placed inside a lead-lined box to avoid this
       • people who work with radioactive sources will sometimes stand behind a lead barrier, be in a different room, or use a remote-controlled arm when handling radioactive substances.

6. alpha decay equations

   • an alpha particle is made of two protons and two neutrons.
     • The atomic number goes down by two and its mass number decreases by four

7. gamma rays

   • there is no change to the nucleus when a radioactive source emits gamma radiation.
     • It is the nucleus getting rid of excess energy

8. contamination

   • when unwanted radioactive atoms get onto an object, it is possible for the radioactive particles to get inside the body
     • protective clothing should be worn when handling radioactive material

9. beta decay equations

   • a neutron turns into a proton and released an electron
     • the mass of the nucleus does not change but the number of protons increases

10. background radiation

    • this comes from natural sources like rocks, food and air. It also comes from man-made sources such as nuclear weapons, nuclear waste or nuclear accidents.
      • The dose of radiation people receive varied dependent on how close they are to the source. Too much exposure to radiation can cause radiation poisoning.
        • Radiation is measured in sieverts (Sv)

11. fission

    • the splitting of large radioactive nuclei into smaller ones
      • a neutron is absorbed by a large unstable nucleus - the nucleus splits into smaller nuclei
        • as this happens, more neutrons and energy are released
          • the neutrons released cause more reactions - chain reaction
      • fission is carried out in a nuclear reactor in order to generate electricity.
        • it is controlled by control rods which, when they are lowered down, slow down the reaction process
          • When they are raised, the reaction speeds up again
            • if this process is not controlled, then a nuclear weapon has been produced

12. fusion

    • nuclear fusion is the joining together of smaller radioactive nuclei to make a larger atom
      • the whole process releases a lot of energy, much more than fission
        • however, a very high temperature and pressure is needed for fusion to occur, so it is not yet used in the production of energy

13. radiotherapy

    • high doses of radiation can be used to treat cancer
      • gamma rays are focused directly onto the cancer cell but not killing too many healthy cells
        • the damage to the healthy cells that may be close to the cancer can cause the patient to feel ill - however, killing the cancer cell makes it worth it

14. uses of nuclear radiation

    • gamma sources can be used as a medical tracer in the human body; isotopes can be injected or swallowed.
      • As the isotope goes around the body, it can be monitored and medical issues can be spotted.
        • Gamma radiation is emitted out of the body and does not cause the cells to become ionised.
          • The isotope used will have a short half-life so it does not stay inside the body for too long.
            • Tracers can be used to diagnose potentially life-threatening conditions which otherwise would not be spotted. The risk of using the radioactive tracer is much less than the risk of the condition they may diagnose.

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