The atom, the Nucleus and Radioactivity

The atom, the Nucleus and Radioactivity

1. The atom

   • The plum pudding model
     • Rutherfords expt.
       • he believed the model and expected the alpha particles to go through the gold foil
       • results - atoms are composed mainly of empty space have an extremely positive centre
         • thought that there was an electron cloud surrounding the nucleus
     • the arrangement of electrons
       • Neils Bohr - believed electrons existed in 'energy levels' this was proofed by the emission spectrum
         • types of spectra
           • Continuous produced by a liquid or solid a continuous spectrum is emitted unable to detect the element stic
           • a line spectrum is produced by gaseous matter, it is charateristic
         • Emission spectrum
           • every element gives out its own unique emission spectrum
             • LASERS- Light amplification by stimulated emission of radiation
               • Produce an intense beam of light, the electrons recive energy and go to the same energy level and then emit the same wavelength photon
                 • used to treat eye problems
                 • used for telecommunication in optical fibers
                 • used in welding and cutting
                 • used in target designation
           • E2-E1=hxf
             • E2-E1 (difference in energy levels) h= planks constant f=frequency
           • c= f x ^
         • Bohrs theory

2. Radioactivity

   • Henri Becquerel discovered that a crystal of uranium was emitting some kind of light. Marie Curie later went on to research more and name this occurance as radiation.
   • natural radiation - the spontaneous decay of a nucleus, with the emission of some form of radiation
   • artificial radioactivity- radioactivity from atoms caused b nuclear bombardment
   • The activity of the radioactive nucleus
     • the number of nuclei of a radioactive sample decaying per second= activity (A) / Becquerel (Bq)
   • The law of radioactive decay
     • no. of nuclei decaying at that moment is proportional to the no. undecayed @ that instant
       • RATE OF DECAY= ^ x N
         • N- the no. of undecayed atoms ^ - decay constant
         • each isotope has its own decay constant
         • the rate decreases as time goes on
         • Half- life (T 1/2) - the time taken for half of the undecayed atoms in an sample of the element to decay

3. Detecting nuclear radiation and uses

   • Geiger-Muller tube or solid state detector
     • - radiation passes through the window of the tube and ionises the gas - the e- are accelerated towards the anode causing more ionization -this induces a small current which measures the pulse time for each ionizing particle -it cant tell the type of radiation
   • medical - cancer treatment
   • carbon dating (c-14)
   • used in fertilisers
   • preservation of spices in food

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