(Portland, OR)  --  A Portland man is headed to prison for shaking his seven-week-old son and causing brain injuries.  Prosecutors charged 23-year-old Norman Brown, Jr. with assault and criminal mistreatment, and he was found guilty last month.  Brown, who was accused of shaking the child on at least two occasions, has been sentenced to seven-and-a-half years behind bars.  The boy is now 13-months-old and is in state custody.