STOCKTON — “OK, next I’m gonna let you taste my burps!” Dr. Proton bellows, lab goggles slightly askew.“Ewwww!” comes the cry from dozens of kids, half-horrified and half-hysterical, torn between volunteering or running away.From getting a quarter to scream to giving the kids a dry ice bubble shower, Dr. Proton — AKA Doug Christensen — kept the budding young brainiacs spellbound during his Mad Science [...]