Eleven major airports will begin using body scanners to screen passengers as the Transportation Security Administration launches a plan to buy 1,000 of the machines over the next two years.The scanners can look under passengers' clothing in order to detect weapons and explosives. Boston Logan International Airport received one new scanner this week and will get two more next week. All will go into the same terminal. Among the other airports getting the scanners are Los Angeles International, Chicago O'Hare and Charlotte Douglas International.