The high powered scanners that cause trouble even in fairly slow films are used for CHECKED baggage. NOT carry on.(posted 8880 days ago)Most carry on machines are labeled with the maximum safe film speed. Typically either ISO 400 or ISO 1600.
Realize that in the US and Canada you can insist on hand inspection, but outside those countries, they may not allow hand inspection. Having the film in a claer plastic bag, and asking nicely with a smile can help, but they DON'T have to do it.
I use a lead bag. Sometimes after running my carry on through the scanner they will hand inspect the contents of the bag, sometimes not. For very high speed film (over ISO 800) I have a couple if film containers that use some barium compound to provide extra protection. These almost always end up causing an additional check of my bag.
I have traveled a lot with 400 film in a lead bag with NO problems, even with multiple checks. I have traveled a good bit with ISO 400 film in cameras and loose (not in lead bag) without any problems either. So the lead bag is probably not needed, but it makes me feel better.
NEVER put ANY uprocessed film in your checked baggage.