Not sure what volcanic dust has to do with anything. because x-rays would penetrate? still there are not a lot of X-Rays around, probably not enough to ‘see’ by. There is not a huge amount of X-Rays normally. They do damage cells, and high levels would be noticeable. That was part of the problem with the Ozone layer hole, Ozone absorbes/reflects most harmful rays (x-rays included). So, i don’t know precisely how much, but it’s not a lot. sensitivity is not the word you’re looking for. An incredibly sensitive eye would simply be very good at seeing visible range. X-rays are just not in that range. X-Rays have higher energy and lower wavelength then visible light rays, and would require a very different sensing mechanism. As far as I can tell, no natural source is capable of detecting X-rays in the way an eye senses visible rays. What kind of sun? er, don’t know enough astrophysics to answer that one. Sorry. X-Rays ionize atoms, and cause the formation of reactive species in cells. These reactive ions can then damage dna (or the DNA can be ionized, itself), in a myriad of ways. The general end result is that the data in the DNA is lost, mutations occur, and every once in a small while, it becomes cancerous. So yes, it does degrade the ability for cells to reproduce, but that isn’t actually the danger. the mutations is causes right then and there are more important, since it can change what is happening in the cell. keep in mind, DNA is not just important for replication. it has all the instructions for how the cell behaves at (almost) all times. Redundancy at that point becomes subject to a hell of a lot of variables. depends on the amount of X-Rays and the tolerance for cancer and so on, so it can’t really be answered. So, hope that helped. What brought the question up, by the way?