SALEM – A Lynn man was sentenced this week to 30 days in jail for exposing himself to a Salem Hospital nurse after his girlfriend gave birth last year, authorities said.Brian Crabtree, 41, was allegedly asleep next to his girlfriend on May 10, 2007 when a nurse walked in to make sure the new mother was doing okay. In the dark, Crabtree allegedly began moaning behind the nurse and brushed up against her leg before performing a “lewd act,” prosecutors said at a Salem District Court hearing.The terrified nurse ran away and had another employee call police, authorities said. She was so scared to identify the suspect face to face that she positively identified him through a video monitor, prosecutors said.The victim now works in a different part of the hospital because of the incident, prosecutors said.Crabtree pleaded guilty to lewd and lascivious behavior in court. He has a 1997 conviction of lewd and lascivious behavior.Judge Richard Mori ordered Crabtree to serve 30 days in prison of a two-year sentence with the balance suspended, according to Essex County District Attorney spokesman Steve O’Connell. Once Crabtree is released, he must serve two years of probation, remain drug and alcohol free and undergo a sex offender evaluation and treatment. He must also stay away and have no contact with the victim or Salem Hospital except for the event of an emergency.