Upper-limit determination of resonant trielectronic recombination cross-section for krypton using crystal channeling

We used channeling through a thin crystal to get an estimate of the cross section of the resonant trielectronic capture by Kr³⁴⁺ ions. K x-ray--K x-ray coincidence measurements were performed with a selection on the charge state and energy loss of transmitted ions. An upper limit of 1.9×10^-27 cm² at the resonance is obtained, and this represents an improvement by two orders of magnitude with respect to previous ion-gas experiments. The possibility to reach the theoretical predictions experimentally is discussed.