Page "Mendelevium" Paragraph 15

There was no direct detection, but by observation of spontaneous fission events arising from its electron-capture daughter < sup > 256 </ sup > Fm.

These events were recorded during the night of February 19, 1955.

The first one was identified with a " hooray " followed by a " double hooray " and a " triple hooray ".

The fourth one eventually officially proved the chemical identification of the 101st element, mendelevium.

Additional analysis and further experimentation, showed the isotope to have mass 256 and to decay by electron capture with a half-life of 1. 5 h.