On the night of November 27, 1419 somewhere near a river bank the water glows bright blue. It was due to a phenomenon known as Cherenkov radiation which was unheard of back then, all these high energy charged particles were emitted from the body of thousands of ghouls as they swam out from the water and slowly marched inland. Despite not carrying any protective gears or armed with anything, the amount of radioaction at close proximity is equivalent to 100 CT scans! Do not wrestle them because surviving reports told of their immeasurable strength and ability to leap tall tower in a single bound, is there any hope for the medieval knights against such a formidable foe? The ghoul's IQ is about 90 give and take using today standard, they don't feel any sensation but can still bleed out and become incapacitated.
Castles are pretty much useless if they can just jump over the walls, so you will have to fight them on an open field, it really depends on how you gonna get a large enough force to fight them. Weapons like longbows, polearms and early versions of muscets might be the weapons you wanna go for to stay away from them as far as possible, although polearms will become useless depending on how fast they are (i assume they are since they can jump the hight of a tower). Here are some other important things you need to tell us to become more accurate with an answer: Can they feel pain? How much arrows does it take to stop them? (Can you cripple them? If so you might wanna use caltrops too) Will they even risk an open battle when they are not that dumb?
It was due to a phenomenon known as Cherenkov radiation
Cherenkov radiation occurs when a particle travels faster than the speed of light in a given medium. Given air's low density and low refractive index, a particle needs to be travelling at about 0.9997c in order to produce the glow you want. Alpha particles won't travel far enough through air to give you the glow you need, beta particles travelling that fast are too energetic for fission or fusion reactions (let alone plain old radioactive decay) and neutrons going that fast will be almost impossible to generate by any means.
What you've got, then, is merely ionised air glow. Don't worry, it still looks as nice.
(incidentally, if they did generate actual Cherenkov radiation, everything around them would just die. forget "100CT scans", whatever that means, think more "active unshielded nuclear reactor in your face")
the amount of radioaction at close proximity is equivalent to 100 CT scans!
"100CT scans" is a very ill-defined amount of radiation, but lets imagine that a knight trying to fight them receives an an entire Sievert. That's enough to cause radiation sickness, but not necessarily enough to kill them
Anyway... chances are, no-one will know. Either they'll see the mystical halos, and run away, or they'll see the ghoul's terrifying strength, and run away, or they'll get splatted by a ghoul. That dose of radiation is high, but not enough to incapacitate promptly. They'll get sick later but won't necessarily die (though regular illness or infection will have a good chance of finishing them off).
Do not wrestle them because surviving reports told of their immeasurable strength and ability to leap tall tower in a single bound, is there any hope for the medieval knights against such a formidable foe?
You haven't said what will kill or incapacitate the ghouls. Maybe they're vulnerable to harsh language?
If arrow-fire can't stop them, then there's nothing to do but get out of their way. Given their leaping ability and mighty strength, they can't really be trapped, or blocked. The radiation is almost entirely irrelevant.
A high wall with a field of pointed stakes on the other side should be enough to deal with them, as they are too dumb to spot the trap.
Lured into leaping over the wall and impaling themselves (and then being bombarded with stones and arrows) , they all die with zero casualties.