The nation's defense against nuclear terrorism took a major step Friday, federal officials said, following the award of contracts worth $1.2 billion to install advanced sensors at U.S. ports of entry to screen for radioactive cargo. The Department of Homeland Security plans to install 1,400 advanced detection systems at 370 border crossings and ports under the program, which has been in development at federal laboratories for several years. The sensors, which cost $350,000 to $600,000 each, will allow inspectors to scan rail cars, trucks and shipping containers with greater accuracy and fewer false alarms, said Vayl S. Oxford, director of...