Isotopes of mercury
There are seven stable isotopes of mercury with 202Hg being the most abundant. The longest-lived radioisotopes are 194Hg with a half-life of 447 years, and 203Hg with a half-life of 46.61 days. Most of the remaining 40 radioisotopes have half-lives that are less than a day. The odd natural isotopes 199Hg and 201Hg are NMR-active, having spin [quantum number|spin] of 1/2 and 3/2 respectively; as NMR is best with spin 1/2, the former is normally used. All isotopes of mercury are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed. These isotopes are predicted to undergo either alpha decay or double [beta decay].