Any one explain this, i havent had a electric fence charger since 2011, it was a older unit a capacitor and a transformer, the charger unit was mounted inside a bulding and back then a stack of Florencent tubes stacked agest the wall beside the unit would flash everytime time the unit would click a 1 seccond flash of spark, what exactly caused that

No, radio waves are not radioactive radiation and do not cause cancer.

The mercury vapor inside the tube is really sensitive to electric fields, not just to electric current running through it. If the electric fence wire runs close enough to it, the field strength (in volts per meter) may be high enough to ionize the mercury vapor.

I'm unsure how many volts per meter you need, but it'll probably be in the order of 100v/m if you're running DC pulses. On radio frequencies it drops, which is how you can light fluorescent tubes so easily with even fairly small transmitters.