After the terrorist attacks of Sept. 11, 2011, security experts said that poor controls over radioactive materials could allow terrorists to enter the country unarmed and obtain the ingredients for attacks locally. The Nuclear Regulatory Commission set out to tighten its rules, and the National Nuclear Security Agency, which is part of the Energy Department, offered grants to buy security equipment.There are about 1,500 hospitals and medical buildings that use radioactive materials, according to the Energy Department, which has spent about $96 million to secure them.