Isotopes of holmium

Natural holmium (₆₇Ho) contains one observationally stable isotope, ¹⁶⁵Ho. The below table lists 36 isotopes spanning ¹⁴⁰Ho through ¹⁷⁵Ho as well as 33 nuclear isomers. Among the known synthetic radioactive isotopes; the most stable one is ¹⁶³Ho, with a half-life of 4,570 years. All other radioisotopes have half-lives not greater than 1.117 days in their ground states (although the metastable ^166m1Ho has a half-life of about 1,200 years), and most have half-lives under 3 hours.

Theoretically, the only "stable" isotope of holmium, ¹⁶⁵Ho, as well as all nuclides in the beta-decay stable isobars with mass number ≥165, can go alpha decay, hence ¹⁶⁴Dy is the heaviest theoretically stable nuclide.