Can't see any traces of particles in my Wilson chamber without radioactive material I am doing an essay about particle physics and I need some help.
I am comparing the results in a Wilsonchamber with and without a radioactive material present. I were able to see a lot of traces from alpha particles, but without the radioactive material there were no traces at all. I've tried to improve my chamber by making it more airtight but could still not see any spontanious particle decay. I am using a plastic chamber that is about 0,5cm thick and for the bottom a sheet metal plate.
I know I am not giving you all information there is about the chamber but what reasons could there be for not seeing spontanious decay while the decay with a radioactive material is so obvious.
 A: Your problem is the "spontaneous decay". You probably mean the natural radioactivity, that can come from the environment or cosmic. 
Since you say the chamber works with alphas (that can penetrate only like 50-100 micrometers of material), I would say it should be tested with electrons and then you must be quite patient to see the cosmic rays. 
A: 
I know I am not giving you all information there is about the chamber but what reasons could there be for not seeing spontanious decay while the decay with a radioactive material is so obvious.

The radioactivity of the plastic etc components of your chamber fortunately is very low, so you should only expect to see cosmics penetrating. Plastics are good shields  it seems for for high energy radiation, which will be the muons that come mostly through the cosmic radiation . So the details of your construction and its location  are needed : if it is in a basement, it might be well shielded too.

Muons arrive at sea level with an average flux of about 1 muon per square centimeter per minute. This is about half of the typical total natural radiation background.

So the area of the top plays a role, from above you should get two traces on average per minute per centimeter, if you are on the roof at sea level.
So you see details do matter, how long have you waited to see something?
what was your radioactive material? Look at this for some numbers
