Here’s the science part of this fiction: The Proton Pack is actually a mini nuclear accelerator comprised of a proton gun attached to a particle accelerator in a backpack. It concentrates protons, shooting them in a visible stream to negate the particles in negative ectoplasmic entities. They look the business too: Slimer was reduced to a bubbling pool of green ectoplasm when he was fried with a proton pack, and the random nature of the streams meant that whenever the four Ghostbusters went a-busting, carnage ensued. Just remember not to cross the streams.