I find it very peculiar that the state department was not notified until 1976. Something more must have been going on behind the scenes that the security services didn't quite want bubbling up yet.
I wonder if perhaps faulty dosimetry was suspected?
Or perhaps the US team brought their own nuclear powered equipment which might have been causing it?
If this were to happen today, it would become a diplomatic incident with each side pointing fingers and blaming the other.