Rutherfordium (Rf) is a synthetic, radioactive metallic element of the transactinide series, atomic number 106. It has a half-life of less than a second. It is thought to have been discovered first in 1974, but its existence was only proved in 1994, the year it was given the name rutherfordium (after Ernest Rutherford). The name rutherfordium had previously been used for element 104 (now known as dubnium).