The hazmat captain tells Ross and Wheeler that the radiation levels in the restaurant are too high for them to go inside. Yet as he stated earlier polonium is an alpha decay particle, meaning that compared to other types of radiation, like beta and gamma rays, its energy emissions are much weaker. Whereas gamma particles can only be stopped by really dense material like lead, and beta particles can be stopped by moderately dense materials like a piece of plastic several inches thick, alpha particles can be stopped by a single layer of skin. So the only way it's harmful is if it is ingested or it gets inside the bloodstream, as long as the detectives wore gloves they'd be fine, the only danger would be getting polonium inside of an open wound, but a normal pair of latex gloves would be more than sufficient protection.
When the hazmat team is scanning the restaurant with their Geiger counters the sound they were making was a high pitched beeping/squealing, like the sound a metal detector makes. When a Geiger counter detects elevated radiation levels it makes a clicking sound. This sound is made because a Geiger counter is a tube filled with an inert gas which has a high-voltage wire running down the center. Whenever a high energy particle, like a radioactive isotope, comes into contact with the gas it creates an electric charge which discharges onto the wire in the middle, that discharge is what makes the clicking sound.