Re: "It begins with shining an infrared laser beam near a radioactive source"
I think the idea is that instead of walking around a container with a geiger counter, or rigging up some way for a robotic arm / drone to move the geiger counter around, you instead have two lasers at opposite corners of the container. They quickly scan the whole container. Or you have two lasers each side of the gate that the lorries drive through, so you scan containers as they leave the port. Or you just have a laser on a van and drive around the port pointing it at things, you don't have to worry about climbing up close to the containers.
Alternatively, you could imagine that with enough development they may be able to make a hand-held device a bit like a FLIR infra-red scanner, which shows the operator a picture of the amount of radioacivity. They stand on the docks and point it at the containers from a distance, and look for radioactive hotspots to investigate further. This could also be useful to people working in radioactive cleanup (e.g. Chernobyl, Fukushima, Sellafield, reactors being decommissioned ...).