There are seven stable isotopes of mercury (80Hg) with 202Hg being the most abundant (29.86%).
Most of the remaining 40 radioisotopes have half-lives that are less than a day.
199Hg and 201Hg are the most often studied NMR-active nuclei, having spin quantum numbers of 1/2 and 3/2 respectively.
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.