why ZnS screen was used by rutherford? 

Because it emits light upon excitation by X-rays or electron beam, making it useful for X-ray screens and cathode ray tubes.

 Zinc sulfide, with addition of few ppm of suitable activator, is used as phosphor in many applications, from cathode ray tubes through x-ray screens to glow in the dark products. Whensilver is used as activator, the resulting color is bright blue, with maximum at 450 nm.Manganese yields an orange-red color at around 590 nm. Copper provides long glow time and the familiar glow-in-the-dark greenish color. Copper-doped zinc sulfide ("ZnS+Cu") is used also inelectroluminescent panels.^[2] It also exhibits phosphorescence due to impurities on illumination with blue or ultraviolet light.

and He found that a screen coated with zinc sulfide emitted a flash of light each time it was hit by an -particle. Rutherford and his assistant, Hans Geiger, would sit in the dark until his eyes became sensitive enough. They would then try to count the flashes of light given off by the ZnS screen. (It is not surprising that Geiger was motivated to develop the electronic radioactivity counter that carries his name.)

this is not at all written by me

i had just copied it  i hope dis will help u :)'

simple!!! zinc sulpide is a flouresent material.. hence it emits light.. when electrons strikes it