The simulation demonstrates how to get information about the size of atoms from the scattering experiments. The scheme of the experiment is quite simple. A small particle is launched towards the solid and after many scattering events you are to figure out the radius of the atoms solid consists of. On the screen you can see a blue barrier which hides a consistency of examined atoms. To remove the barrier and see the atoms select the checkbox labeled ?Remove barrier?. On pressing the ?Reset? button size of the atoms is changed. You are to run the simulation with different atoms many times to get enough information and to calculate the size of the atoms behind the barrier. Choose the answer on the floating band control. To find out if your answer is correct press ?Check answer? button. The result of checking will be displayed in the output window. Remember! To be able to give the correct answer you should collect enough information about the process of scattering.