P4 - Atomic Structure and radiation

P4 - Atomic Structure and radiation

1. structure of the atom

   • nucleus
     • proton
       • mass=1
       • charge=+1
     • neutron
       • mass=1
       • charge=0
   • electron
     • mass=close to 0 (1/2000
     • charge=1

2. history of the atom

   • Democritus 400BC
     • "atoms are invisable
   • John Dalton 1803
     • "atoms are building blocks there are different types
   • JJ Thomson 1898
     • Plum pudding modal a ball of plus charge dotted with one minus charges
   • Ernest Rutherford 1909
     • a tiny nucleus has all the mass and plus one charge
   • Niels Bohr 1922
     • electrons are in shells
   • James Chadwick 1922
     • discovered newtrons

3. types of radiation

   • gamma
     • mass- 0
     • charge-0
     • weekly ionising
     • stopped by a few meters of thick lead
   • beta
     • fairly ionising
     • fast moving electron
     • mass-1/1832
     • charge-1
     • stopped at AL foil
   • alpha
     • charge- 2+
     • stopped by a few cm of air
     • most ionising
     • mass-4