u/Key-Caterpillar5643

dear dentists, any ideas what this black spot on the chin could be? anything alarming?

the device seems to have been opened in the past, so a VERY nasty Sr90 source is either still inside or has been slowly flaking off and contaminated the whole box. the base of this box is always the hottest, but i'd rather not touch it, nor am i ever getting any closer to this sh*t