Michael Paul (Israel): Noble gas accelerator mass spectrometry of argon isotopes in an inertially confined fusion plasma

We observe production of the unstable neutron-rich ⁴²Ar nuclide in an argon-doped plasma created by laser-induced inertially confined deuterium-tritium fusion at the National Ignition Facility (NIF, USA). The experiment searched for neutron-induced reactions on ⁴⁰Ar producing ³⁹Ar (t_1/2= 268 y), ⁴¹Ar (t_1/2=110 min) and ⁴²Ar (t_1/2=33 y). Argon-42 in particular is considered a candidate for the observation of rapid neutron captures in physical conditions similar to those of the stellar r-process. The yields of long-lived ³⁹Ar (2.8±0.1x10¹⁰ atoms) and ⁴²Ar (1.6±0.5×10⁶ atoms) produced in a NIF experiment were determined by Noble Gas Accelerator Mass Spectrometry based on highly-charged positive ions at Argonne National Laboratory (USA). Argon-41 was counted by γ spectrometry at NIF. While the production modes of ³⁹Ar (fast-neutron (n,2n) reaction) and ⁴¹Ar (neutron capture (n,γ) reaction) are understood, ⁴²Ar is presently believed to be produced by a complex sequence of reactions in-flight in the dense plasma, which will be described in this talk.