) and that is a little radioactive with a particularly very long 50 percent-lifetime, as well as traces of radioisotopes that are made by cosmic rays within the ambiance. 69Kr 70Kr 71Kr 72Kr 73Kr 74Kr 75Kr 76Kr 77Kr 78Kr 79Kr 80Kr 81Kr 82Kr 83Kr 84Kr 85Kr 86Kr 87Kr 88Kr 89Kr https://socialinplace.com/story14138715/details-fiction-and-%EB%A7%A5%EC%8A%A488-%ED%9B%84%EA%B8%B0