Attempts to investigate RDEC for single-layer graphene impacted by F^9,8+ ions^*

Radiative double-electron capture (RDEC) occurs when the capture of two electrons by an ion occurs simultaneous with the emission of a single photon. This process, fundamental in atomic collisions, is considered as the inverse of double photoionization by a single photon in ion-atom collisions. RDEC has been successfully studied with gas¹ and thin-foil² targets, and only recently studied for single-layer graphene targets.³ The preliminary RDEC results for 2.11 MeV/u F^9,8+ ions on graphene indicated cross sections that were too large, approaching values found for thin-foil targets when the thickness of the graphene was about a hundred times smaller. In the present work we have repeated the RDEC measurements with single-layer graphene as well as identical targets that had no graphene on them. The work was done at WMU with the 6-MV tandem van de Graaff accelerator. Graphene (∼0.35 nm thick) was mounted on a silicon nitride grid (200 nm thick) consisting of ∼6400 holes of 2 µm diameter on a 200 µm thick substrate. A Si(Li) spectrometer placed at 90° to the beam detected the emitted x rays while the magnetically separated outgoing charged particles were counted using silicon surface barrier detectors. Co[JAT1] incidences between x [JAT2] rays and charge-changed particles were observed with event-mode acquisition. The new results point to significantly smaller cross sections than those seen earlier. Reasons for this difference will be explored. ¹D. S. La Mantia et al. 2020, Phys. Rev. Lett. 124, 133401; ²D. S. La Mantia et al. 2020, Phys. Rev. A 102, 060801(R); ³D. S. La Mantia et al. 2021, ViCPEAC 2021, Book of Abstracts, p. 108.