In 1958, scientists from the Berkeley Lab in California set out to verify the results from the Nobel Institute but could not reproduce the findings of the Nobel group. The Berkeley radiation, who had been reporting discoveries of new elements for almost two decades, produced an isotope of the new element having an atomic mass of 254 and a half-life of 3 seconds. The claim to prior discovery was subsequently awarded to the Berkeley group.
Nobelium is near the end of the actinide series. It is a transuranium element because it is an element heavier than uranium. All known isotopes of nobelium are radioactive.