Continuous X-Ray?

On my flight to Ireland from LAX a couple of weeks ago I sent my backpack with 200 sheets of 4x5 film, camera, and Pentax spotmeter through the x-ray machine. During the trip through the machine the operator stopped it and took a second look at the monitor. I think it was the meter she was looking at with a trigger, a handle and a short barrel, (lens). Anyway she went to get her supervisor and the two discussed my belongings for a while before allowing it to pass through. My question is does the machine take a snapshot of my backpack, or was the x-ray on the whole time they were looking at it? It must have been 30 seconds or more before they let it through.

It's a snapshot.

In fact, when they change the look of the image on the screen, it's a digital enhancement of the same exposure.

It seems unlikely that they would be allowed to run continuous Xrays in such equipment. The health consequences down the line for those who operate the equipment would discourage anything of that kind.