Speaker
Description
The upcoming operation of the nuCARIBU facility at ATLAS will enable new measurements of neutron rich La isotopes, which are important both for U.S. stockpile stewardship applications and for understanding the nucleosynthesis of heavy elements in the cosmos. In particular, constraining the $ ^{146} $La(n,$ \gamma $)$ ^{147} $La and $ ^{147} $La(n,$ \gamma $)$ ^{148} $La reactions through experimentally determined nuclear level densities (NLDs) and $\gamma$-ray strength functions ($\gamma$SFs) will improve neutron reaction network calculations in the $ A = 147 $ mass region under neutron rich conditions.
These nuclei lie in a structurally interesting region of the chart of nuclides, between Mo and Nd, where isotopic chains have exhibited distinct trends in their low energy enhancement (LEE) of the $ \gamma $SF. For Mo and Nd isotopes, the LEE decreases with increasing neutron number. In contrast, measurements of Sn isotopes show no clear evidence of an LEE, a behavior also observed in $ ^{140} $Ba in an Oslo style experiment at CARIBU at ATLAS. For La, Oslo style measurements of $ ^{138,139,140} $La at the Oslo Cyclotron Laboratory indicate either a modest LEE or a plateau like behavior at low $ \gamma $ ray energies.
To extend these systematics further from stability, preparations are underway for an experiment that will use the $ \beta $ decay of $ ^{147,148} $Ba beams to populate excited states in $ ^{147,148} $La. The resulting $ \gamma $ rays at high excitation energies will be studied via total absorption spectroscopy with the Summing NaI (SuN) detector and the SuN Tape system for Active Nuclei (SuNTAN). I will present the experimental concept for this upcoming campaign at nuCARIBU, planned for the second half of this year, and discuss anticipated challenges specific to this region, eight neutrons away from stability.