Radiative Double-Electron Capture (RDEC) by single-layer graphene incident with F^9,8+ ions*

Radiative double-electron capture (RDEC) takes place when the capture of two electrons by an ion is accompanied by the simultaneous emission of a single photon. This process is considered the inverse of double photoionization by a single photon. RDEC has been successfully studied with F^9,8+ ions on gas [1] and thin-foil [2] targets and recently it has been investigated for single-layer graphene [3]. This work is done using the 6-MV tandem van de Graaff accelerator at WMU. A graphene target (∼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 in coincidence with magnetically separated outgoing charge particles counted with silicon surface-barrier detectors.

In the present work, the RDEC measurements have been repeated with single-layer graphene as well as targets that had no graphene on them. A tentative cross section can be calculated for the F⁹⁺ projectile, and the differential value at 90° is 1.3 b, corresponding to a total cross section (assuming isotropy) of 11 b. The value for F⁹⁺ incident on graphene reported here are more in line with earlier values found for the carbon target and are larger by a factor of about four than for the gas targets. Given the thickness of the target, these values appear reasonable.

[1] D. S. La Mantia et al., Phys. Rev. Lett. 124, 133401 (2020)

[2] D. S. La Mantia, P.N.S. Kumara, C.P. McCoy, J.A. Tanis, Phys. Rev. A 102, 060801(R) (2020)

[3] D. S. La Mantia, A. Kayani, K. Bhatt and J. A. Tanis, Atoms 11, 6 (2023)