Dubnium is a chemical element. It has been named eka-tantalum, hahnium and unnilpentium but is now named dubnium. It has the symbol Db. It has the atomic number 105. It is a very radioactive element that does not exist in nature. It has to be made. The isotope that has the longest half-life only has a half life of 32 hours. Dubnium is a transactinide element.