When was californium discover?

Answer 1

it was discovered on the 9th day of February in 1950
Discovery of californium: Stanley G. Thompson, Kenneth Street, Jr., Albert Ghiorso, and Glenn T. Seaborg - February 9, 1950.

Answer 2

Californium (the isotope Cf-245) was prepared for the first time at Berkeley Radiation Laboratory, USA in 1950 by Glenn Seaborg, Stanley Thompson, Albert Ghiorso, Kenneth Street.