The fourth element, dubnium, has been synthesized in laboratories, but it has not been found occurring in nature, with half-life of the most stable isotope, dubnium-268, being only 29 hours, and other isotopes even more radioactive.
Unsur keempat, dubnium, telah disintesis di laboratorium, namun belum ditemukan di alam, dengan waktu paruh isotop yang paling stabil, dubnium-268, hanya 29 jam, dan isotop lainnya bahkan lebih radioaktif lagi.