Mendelevium (Md). It is named after Dmitry Mendeleyev (key developer of the periodic law), and being an artificially created element, was first discovered in 1955 at the University of California in Berkeley, when einsteinium-253 was bombarded with alpha particles. Although the isotope created in this cyclotron had a half-life of approximately 1.3 hours, the most stable isotope (258) has a half-life of 54 days.

Information gleaned from the voice in my head that tells me to do bad things, and Encarta.