Right-angled fork track

    Objective
     To demonstrate that an alpha particle and a helium molecule have the same mass

    Material 
     diffusion cloud chamber with cover 
     radiation source 
     two blotting paper viewers 
     strong light source (300 W to 500 W) 
     dry ice 
     alcohol
     helium
   
    Procedure
     1.Soak the felt ring with alcohol. 
     2.Place the felt ring in the chamber and cover. 
     3.Put dry ice at the bottom of the chamber.
     4.Insert the radioactive source through the hole in the side of the chamber. 
     5.Focus the strong light through the chamber. 
     6.Observe vapour trails against the black bottom of the chamber. 

    The set-up is similar to the previous cloud chamber experiment, except that the 
    cloud chamber is filled with helium gas.


Instruction:
Press ACTION button to stimulate pushing a ring magnet to hit another identical ring magnet on a glass surface covered 
with a thin layer of polystyrene beads.

Press RESET button to set the experiment back to original position.


   
   
   
<IMG SRC="fork.gif" WIDTH=500 HEIGHT=350 BORDER=0>




   Special Note: This collision between an alpha particle and a helium molecule
                           occurs rarely.

Analysis

The right-angled fork track can be explained using the above analogue experiment. 
After collision, the two magnets move off at right angles to each other. This shows 
that the colliding particles - alpha particles and helium molecule - have the same mass. 
This confirms that alpha particles are helium nuclei.




 *back to* [experiment]  [online lab]                               (C) 1999 ThinkQuest Team 27954