Approaching r-process nuclei at N=126
Abstract
The production of heavy neutron-rich nuclei approaching the r-process waiting point at N$\approx$126 has been investigated in fragmentation reactions of relativistic 238U and 208Pb projectiles. Using this technique we were able to identify 73 new heavy neutron-rich nuclei expanding considerably the north-west frontier of the chart of nuclide. Moreover, we were able to determine the half lives of 13 of those nuclides. The measured values are significantly shorter than the predictions used for r-process model calculations. These shorter half lives are understood as due to the role of first-forbidden transitions in the decays of these nuclei. The confirmation of these results for r-process nuclei at N$\approx$126 would indicate that the r-process at this point is faster than expected, leading to a larger production of the heaviest nuclei.