Complex sentence: Ununseptium is the second-heaviest element of all created so far and is radioactive, having a half-life less than a second: nonetheless, this is still longer than the predicted value used in the discovery report.
Split into simpler sentences: Ununseptium is the second-heaviest element of all created so far and is radioactive, having a half-life that appears to be less than one second. Nonetheless, this is still longer than the predicted values used in the discovery report.