[Hari Krishna (OP)]

will the tungsten react with inert gas in light bulb (incandescent)  in the presence of ionising radiation ?

[Bored chemist]

Yes and no. It will donate an electron back to the ionised gas.
No actual compound will be produced.

[evan_au]

Even without ionizing radiation, or reaction with the inert gas, hotspots in the tungsten filament will cause the tungsten to evaporate (making the hotspot higher resistance and even hotter, causing more evaporation...) until the filament fails.

This causes visible darkening of the glass.

See: http://en.wikipedia.org/wiki/Incandescent_light_bulb#Reducing_filament_evaporation