X-ray emission from charge exchange of highly-charged ions in atoms and molecules

Charge exchange followed by radiative stabilization are the main processes responsible for the recent observations of X-ray emission from comets in th eir approach to the Sun. A new apparatus was constructed at JPL to measure, in collisions of HCIs with atoms and molecules, (a) absolute cross section s for single and multiple charge exchange, and (b) normalized X-ray emissio n cross sections. The ions are produced by the JPL HCI Facility and passed through a neutral-gas target cell. The product charge states are analyzed b y a retarding potential difference technique. Results are made absolute by measuring target pressure, and incident and product ion currents. X-rays em itted from the product ions are detected with a Ge solid-state detector hav ing a resolution of approximately 100 eV. X-ray astronomy has taken major s teps forward with the recent launch of the high-resolution satellites Chand ra and Newton. The cross sections reported herein are essential for the dev elopment of the solar wind comet interaction models inspired by these obser vations.