This lightweight, portable system can rapidly detect the presence of nuclear materials in sealed containers without the use of harmful x-rays. Using sensors arrayed linearly and encased in fabric, the RadRope system can be dangled in the 2- to 4-inch gap between stacked shipping containers on a cargo ship by a customs inspector. As the inspector walks along the top containers, a hand-held PDA shows an alarm when any sensor in the array detects radiation levels above background radiation.