Californium

**Definition:** A man-made radioactive actinide with atomic symbol Cf, atomic number 98, and atomic weight 251. Its valence can be +2 or +3. Californium has medical use as a radiation source for radiotherapy.

**Tree numbers:** - D01.268.271.100.150 - D01.268.556.156 - D01.496.749.305.100.150 - D01.552.020.200 - D01.552.544.156