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.