Study of the single-neutron excitation of ²⁰⁷Hg and the fission barrier of ²⁸⁹U using solenoidal spectrometers

Experimental knowledge of the basic nuclear properties of nuclei south and east of ²⁰⁸Pb remains elusive. These nuclei have hitherto been challenging to produce, yet playing a crucial role in understanding the third r-process peak. Properties such as mass, decay rates, and single-particle levels, play a crucial role in evolving our understanding of the third r-process peak. Fission has also been postulated to play a crucial role. At present, theoretical models outpace experimental data, yet the latter is crucial to help benchmark these models. In this talk, I highlight new experimental approaches to elucidate information on single-particle and fission properties of nuclei relevant to the third r-process peak, centered on the solenoidal spectrometer technique [1]. A trio of solenoidal spectrometers has been established to capitalize on the availability of exotic beams at Argonne (HELIOS), FRIB (SOLARIS), and ISODLE (the ISS). I will showcase two recent, successful demonstrations utilizing this approach. The first focuses on the extraction of neutron-single-particle energies for ²⁰⁷Hg [2], while the second highlights the determination of the fission barrier for ²³⁹U [3].