Yes, most likely a relatively weak sealed rad source for detector calibrations and daily QC checks, and not likely to be much to worry about.
I couldn’t see any reason for them to have something like a radiography source on an Osprey.
But military officials those reports of nuclear or radioactive materials were in error. “Contrary to initial reports, there was no nuclear material on board the aircraft. More information will be made available as we receive it,” wing officials said in the statement.
These Ospreys flying between Miramar and El Centro, like most other aircraft, frequently become a defacto FEDEX truck, and deliver pretty much anything. RIP to the 5 lost souls.