A Mexican drug addict who smuggled immigrants was sentenced to three years in prison yesterday for triggering a hoax that prompted a national security alert, a coast-to-coast manhunt and fears that terrorists would detonate a nuclear bomb in Boston. José Ernesto Beltran Quiñonez, 34, apologized in San Diego federal court during the sentencing for falsely telling a 911 operator in January 2005 that two Iraqi men and four Chinese chemists were awaiting an atomic bomb.