Monoisotopic targets production from atomic and molecular positive ion implantation in a tandem accelerator at low energies

Abstract

We produced monoisotopic targets of ¹³C and ^28,29Si with 10¹⁵⁻¹⁶ atoms/cm² areal density by ion implantation in different matrices at the Accelerator Mass Spectrometry (AMS) facility in Mexico. The tandem accelerator terminal voltage was set at the lowest achievable value (200 kV) that yield beams with energy of 435 keV. It is possible to do ion implantation at lower energies in our facility through the use of molecular beams, so in this work we looked for, and successfully found, bound positively charged molecular beams, although with very low intensity. We inject 235 keV ${\mathrm{C}}_6^{-}$ molecules into the charge of exchange canal (argon) of our tandem accelerator and detected the survival fraction of C₂,₃,₄ molecules in 1⁺ and 2⁺ charge states or above. Our results showed that some molecules remain bound, with one or more electrons missing, after being forced through a low density gas stripper at relatively high energy. In the production process of negative molecular fluxes in the Source of Negative Ions by Cesium Sputtering (SNICS) we found an odd-even effect in their intensity that we understand as the coupling between the fragment size distribution of a dynamic fragmentation of graphite by cesium impact and the electron affinity of the molecules with n-carbon atoms. The availability of these kind of high energy molecular beams opens the door for discovery both in the study of the physics of negative and positive molecular ions.