All I know is that detecting the deflecting alpha particles was a very tedious process, so much so that that was probably one reason why he asked Hans Geiger and Ernest Marsden to do the experiment. Modern day recreation of the experiment uses light detectors. (In the 1950s they gave white lines on a TV screen when alpha particles were detected and presently a doorbell sound. Or at least that's what I found on YouTube.)
I am curious about how the deflection was detected in the original experiment. My textbook says they used a microscope. But how? Wouldn't they have to place the microscope inside the vacuum chamber?
Also secondly where were the scintillating effects produced? Was it produced on a zinc sulphide coated screen or somewhere else?