Fermium

**Definition:** A man-made radioactive actinide with atomic symbol Fm, and atomic number 100. Its known isotopes range from 244-254 and 256-258. Its valence can be +2 or +3. Like einsteinium, it was discovered in 1952 in the debris from a thermonuclear explosion.

**Tree numbers:** - D01.268.271.100.275 - D01.268.556.266 - D01.496.749.305.100.275 - D01.552.020.394 - D01.552.544.266