Lawrencium

**Definition:** A radioactive actinide discovered in 1961. It has the atomic symbol Lr, and atomic number 103. There are twelve isotopes with mass numbers 252–262 and 266.

**Tree numbers:** - D01.268.271.100.500 - D01.268.556.423 - D01.268.956.295 - D01.496.749.305.100.500 - D01.552.020.507 - D01.552.544.423