There are seven stable isotopes of mercury, with 202Hg being the most abundant (29.86%). The longest-lived radioisotopes are 194Hg with a half-life of 444 years, and 203Hg with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives that are less than a day.
For the synthesis of precious metals two stable mercury isotopes are of potential interest - the trace isotope 196Hg and the more abundant 198Hg. Both are “one neutron removed” from 197Hg, a radioisotope which decays to 197Au, the only known stable isotope of gold.
30 minute measurement with a High Purity Germanium (HPGe) radiation detector.