I've never had my carry-on scanned on arrival. However, I am wondering if there are airports that x-ray checked in baggage on arrival.
Yes, many airports around the world X-ray bags on arrival.
In some countries, check-in bags are X-rayed before you collect them - sometimes for all flights, sometimes just for select flights. This is the case in the USA for example, and you will generally not be aware whether your bags have been X-Ray'ed or not.
In some other countries, all bags (including carry-on bags that are at least a certain size) are X-Ray'ed as you leave the baggage area. In these cases it's very obvious to you that the bags are being scanned, as you will be asked to put your bags onto the X-Ray machine.
Other countries may only X-ray bags of select passengers after you have collected your checked-in bags, generally once you are in the customs area. How passengers are selected will vary depending on the country and the airport.
In all cases they these X-rays are done to detect items that may not legally be allowed into the country, and/or which need to be declared before entry. This could includes drugs, weapons, food, etc, depending on the country.
I am not sure this is actually the case for USA, as it makes little sense to me: the luggage which is re-checked would be scanned upon rechecking, and for one which is not going into a plane, why TSA would care? Jan 11, 2019 at 21:10
2@George Y. As the answer says, it’s not for security, it’s for customs. In order to detect illegal imports. Jan 11, 2019 at 22:13
@GeorgeY. The US doesn't routinely X-rays bags, but they do so just for select flights. The point is generally the detection of drugs rather than security (which is what TSA is more interested in), and thus flights from drug source countries are more likely to be targeted.– DocJan 11, 2019 at 22:39
@Doc this makes little sense - scan only luggage but not scan carry-on? Again, do you have any source? Jan 11, 2019 at 22:48
@GeorgeY. I don't have a source, but US Customs does have some mobile x-ray equipment that can be used at the gate as bags are unloaded from the plane to identify checked bags of interest. I believe this has been shown on one of the "border security" TV shows, though I couldn't tell you exactly which episode or anything. They also have x-ray equipment in the customs area, and can use that on both checked and carry-on bags. Jan 11, 2019 at 23:07
Quite a few do X ray both checked in and carry on luggage. It happened to me in Brasilia airport I remember vividly. I think one or two others however I forgot. Actually just last month in Las Americas airport in Santo Domingo they did.