Can airport x rays detect small amounts of marijuana?

It depends on the machine. Different materials are penetrated differently by x-rays, and some machines are tuned to pick up on the level of resistance typically caused by Marijuana.

The latest x-ray technology uses backscatter technology. They not only capture the radiation that goes through an object, but what bounces back as well. Then a computer cleans up the image. So things like bricks of illegal drugs can by found inside of vehicles using x-ray trucks.