Specific Cloud Chamber?

From MariachiWiki

Could one possibly use magnetic fields in order to block non-high energy particles from entering the area in which the ionizing radiation would be obsevered there by only observing cosmic radiation? If so could another field be placed INSIDE the area housing the viewing equipment such as a cloud or bubble chamber to then count the number of particles that are then entering the area to determine which are possitivly or negativly charged and then find if there is a certain out come that is more likely than the other? (doesnt even seem to work in my mind so who knows what will happen in "reality")