Speaker
Description
The existence of long-lived super heavy elements depends on the presence of shell gaps that increase nuclear stability against fission. The largest effects are expected in the so-called Island of Stability (IoS), where the next main spherical gaps are predicted to exist, near proton number $Z$=114, 120 and neutron number $N$=184. Small energy gaps occurring near $Z$=100,108 and $N$=152,162 also enhance the stability of heavy actinides and trans-actinides, creating a sort of "submerged rift" leading to the IoS. Notably, valence orbitals of nuclei in the heavy actinide region include some substates, lowered by deformation, of orbits predicted to give rise to the IoS. The properties of actinides near the deformed shell gaps thus provide imporant benchmarks for theoretical models that predict the location of the IoS and the properties of super heavy elements.
At the JAEA Tandem facility in Tokai, Japan, we have performed a number of $\gamma$-ray spectroscopy studies to deepen our understanding of the structure of actinides in the region near $^{252}$Fm, produced using multi-nucleon transfer reactions. In particular, we focused on the influence and role of the $Z$=100 and $N$=152 deformed shell gaps. Recent results, which include new information on $K$ isomers in $^{248}$Cf ($Z$=98,$N$=150)[1] and the ground state rotational band of deformed doubly magic $^{252}$Fm, will be presented.
Experimentally, one factor that limits the study of heavy actinides is the low detection efficiency for low-energy transitions (<60 keV), which are typical of rotational bands in this region. A possible solution, provided by an array of CdTe detectors that we are currently develping, will also be introduced.
[1] R. Orlandi et al., Phys. Rev C 106, 064301 (2022).
