Radioactivity

Radioactivity

1. Three types of particles make up and atom

   • Protons
     • found in the nucleus  Relative mass 1 Relative charge +1
   • nutrons
     • Found in the nucleus  Relative mass = 1 Relative charge = 0
   • Electrons
     • Surrounds the nucleus  Relative mass= Alsomost zero Relative charge = -1 

2. Unstable nucleus

   • Some materials are radioactive because the nucleus of each atom is unstableand can decay, or split up, by giving out nuclear radiation in the form of alpha particles, beta particles or gamma rays.
   • example
     • If a radioactive material has an activity of 200 Bq, in 1 second 200 of its nuclei will decay and give off radiation. In 1 minute 12,000 (= 200 x 60) nuclei will decay. The activity of a radioactive material will decrease with time. This will be shown by a falling count rate, measured using the Geiger counter.

3. Three types of radiation particle

   • Alpha
     • 2 nutrons to electrons same as a helium particle.  Weak penertration Very ionising 
     • alpha decay
       • When an alpha particle is emitted from the nucleus it, the nucleus,  looses to neutrons and two protons from the nucleus. This means that its atomic number goes down by two and its mass number goes down by 4. 
       • example
         • radon goes to polonium because of alpha decay.  We see in the equation that a helium particle is lost. 
   • beta
     • This is a very fast moving electron  Moderately penertrating Moderately ionizing 
     • beta decay
       • In Beta decay a neutron changes into a proton plus an electron. The proton stays in the nucleus and the electron leaves the atom with high energy, and we call it a beta particle. When a beta particle is emitted from the nucleus the nucleus has one more proton and one less neutron. This means the atomic mass number remains unchanged and the atomic number increases by 1.
       • exapmle
         • Carbon-14 is a radioactive isotope of carbon. (It's a carbon atom with 8 neutrons instead of the usual 6.) This due to beta decay produces one electron and Nitrogen
   • Gamma
     • High energy electro magnetic radiation most penetrating Weak ionising ability

4. ionisation ability

   • Ionising radiation is radiation that has enough energy to cause other atoms to lose electrons and form ions.

5. How an atom is represented

   • A = atomic mass (number of protons + neutrons) Z = atomic number (number of protons) X = chemical symbol (as shown on the periodic table)

6. penetrating ability

   • alpha
     • Alpha has a very weak penetrating ability.  It can be stopped by your hand or even just a piece of paper. 
   • gamma
     • Very high penetrating ability. It can go through most materials. Can be stopped/absorbed by lead because of its very high density. 
   • beta
     • As per most of abilities is it in-between gamma and alpha particles. It can go through your hand and a sheet of paper for example but it can be stopped by aluminium which is of medium density. 

7. Deflecting radiation

   • electircal fields
     • Alpha particles= positve charge Beta particle= negative charge  Gamma particles= nuetral charge This means that alpha and beta particles can be deflected and gamma cannot.
     • alpha goes to oppositely charged negative plate
     • beta goes to oppositely charged positive plate
   • magnetic fields
     • Because they consist of charged particles, alpha radiation and beta radiation can also be deflected by magnetic fields. Just as with electric fields, gamma radiation is not deflected by magnetic fields.

8. Detecting radiation

   • Photographic film
     • People who work on radioactive plants will wear badges with photographic film inside. The darker the film the higher amounts of radiation they have been exposed to. The get an accurate measure of how much radiation they are receiving the badges will have different materials such as Alumminium and copper. 
   • Geiger-Muller tube
     • The Geiger-Muller tube detects radiation. Each time it absorbs radiation, it transmits an electrical pulse to a counting machine. This makes a clicking sound or displays the count rate. The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Muller tube is absorbing.

9. hazards

   • When a radioactive particle reaches a cell it can damage the cell and potentially make the cell cancerous. 
   • inside the body
     • Alpha
       • When inside the body it can cause great health problems due to its high ionising ability and the fact that it has nothing to penetrate. 
     • Betta and Gamma
       • Betta and gamma particles due to there low ionising ability don't have  that great effect when the body. 
   • Outside the body
     • ALpha
       • Not very dangerous because it cannot penetrate the body 

10. half life

    • There are two definitions of half-life, but they mean essentially the same thing: the time it takes for the number of nuclei of the isotope in a sample to halvethe time it takes for the count rate from a sample containing the isotope to fall to half its starting level
    • graphs
      • It is possible to find out the half-life of a radioactive substance from a graph of the count rate against time. The graph shows the decay curve for a radioactive substance.

11. the use of the substances

    • in smoke detectorsfor sterilising medical instrumentsfor killing cancer cellsfor dating rocks and materials such as archaeological findsin chemical tracers to help with medical diagnosisfor measuring the thickness of materials in, for example, a paper facto

12. Nuclear Fission

    • Used in power plant  Fission- means the splitting of
    • process
      • Uranium or plutonium is used because they're atoms have rather large nuclei and are very easy to split up.
      • hit by a neutron
        • This causes the nuclei to: Split into two smaller nuclei known as daughter nuclei which are radioactive. Two or three more neutrons are released Energy is released in the form of kinetic energy.   
        • The extra flying neutrons cause more collisions
          • The more neutrons there are the higher chance of they're being more collisions with the other uranium atoms this means that they're is a chain effect occurring leading to more and more kinetic energy being produced. 
        • The rate of reactions is controlled
          • The 'controllers' will insert and remove carbon rods into the container to maintain a steady rate of reaction. 
    • how energy is harvested
      • Nuclear reactors use the heat from nuclear reactions in the nuclear fuel to boil water. Just as in conventional power stations, the steam from the boiling water makes a turbine spin, which in turn makes the generator turn.
      • Waste products
        • No CO2 is produced unlike many energy making processes.  Plutonium can be used to make nuclear bombs. Other waste products are strored in barrels underground. 

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