are you waiting to bottle it and your ferm. lock still shows signs of bubbling?
i would suggest transferring it to another carboy or bucket to get it off the yeast bed.
if there is active yeast it will finish quicker.

you really can't just stop it. if there is active yeast and you bottle it, it will blow your caps off.
guaranteed

without radiation? that depends

if its a top fermenting yeast, getting it REALLY cold "can" work, like just above freezing, I've done this to shock a dark brown ale I was working on, wanted it to end a little sweeter, worked really well, basically stopped fermentation, did not kill all the yeast it seems however, once I warmed one of the then capped bottled to room temp for a few days I blew the cap off, along with about an inch of bottle neck

if its a bottom fermenting yeast you may be SOL, the little bastards like the cold, I tried the same trick as before with a dopplebock and it barely affected them, relatively speaking, I mean really you can barely tell a bottom is fermenting anyway, lol


I've heard mixed results from UV bulbs, usually guys going from keg to keg with one of those UV lamps inline

but really the best way to stop fermentation, is to run out of sugars, sure fire way to stop it in its tracks

i'm not a fan of the stuff, but i'm guessing you could rack it and then dose it with some camden tabs (sulfite). They are often used in wine making to kill the wild yeasts present on the fruit.