Radiative Double Electron Capture (RDEC) in 40 MeV $\rm{\bf F}^{\bf 8+}$ and $\rm{\bf F}^{\bf 9+}$ + Ne Collisions

The capture of two electrons with the simultaneous emission of a single photon is known as radiative double electron capture (RDEC). This process is the time-inverse of double photoionization and gives insight into electron correlation. Preliminary RDEC cross sections were measured for $\rm{F}^{8,9+}$ colliding with neon. The corresponding RDEC cross section for $\rm{F}^{8+}$ is about 4 times smaller than that for $\rm{F}^{9+}$, as expected as capture of both electrons to the projectile K shell is not allowed. This work was performed at Western Michigan University (WMU) using the tandem Van de Graaff accelerator. Beams of 40 MeV $\rm{F}^{8+}$ and $\rm{F}^{9+}$ collided with neon inside a differentially pumped cell. Surface barrier detectors were used to observe the charge-changed projectiles and a Si(Li) x-ray detector, placed at $90^{\rm{o}}$ to the incident beam, was used to measure photons coincident with the charge-changed ions. Previous RDEC experiments with gaseous targets failed to find conclusive evidence for this event,\footnote{G. Bednarz, {\it et al}. NIM B, {\bf 205} 573 (2003)} while successful observations were performed at WMU using a solid carbon target.\footnote{A. Simon, {\it et al}. PRL {\bf 104}, 123001 (2010)}