The other naturally occurring isotopes have not been observed to decay, constraining their half-lives to be::182W, t1⁄2 > 1.7×1020 years:183W, t1⁄2 > 8×1019 years:184W, t1⁄2 > 1.8×1020 years:186W, t1⁄2 > 4.1×1018 yearsAnother 30 artificial radioisotopes of tungsten have been characterized, the most stable of which are 181W with a half-life of 121.2 days, 185W with a half-life of 75.1 days, 188W with a half-life of 69.4 days, 178W with a half-life of 21.6 days, and 187W with a half-life of 23.72 h. All of the remaining radioactive isotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes.