You may have noted the effect of triboluminescence, in which peeled tape emits visible light.
In a vacuum, it also would appear to emit x-rays.
As the tape peels the acrylic adhesive on the exposed tape becomes positively charged and the outer surface of the remaining polyethylene roll acquires a negative charge. This causes electric fields to build up to values that trigger discharges.
At the reduced pressure in the experiment--about one millionth of an atmosphere--the discharges accelerate the electrons to energies that generate X–rays when they suddenly decelerate in the positive side of the tape.