Average charge and its structure dependence of fragment ions under irradiation of a thin carbon foil with a 1-MeV/atom C cluster ion

Chiba, Atsuya; Saito, Yuichi; Narumi, Kazumasa; Adachi, Masahiro; Kaneko, Toshiaki*

The charge states of fragment ions were measured for 1-MeV/atom C cluster ions penetrating a carbon foil of 2.4-g/cm thickness. Those ions were detected with a luminance plate detector monitored by a CCD camera. The detected ion signals were traced by coulomb explosion imaging technique, which enabled us to classify charge states of each fragment ion and spatial structure of a cluster ion on emerging from the foil. Using this technique, for the first time, we found that (1) the measured average charges of the fragment ions in a triangular structure are smaller than those in a linear-chain structure, and (2) the edge-position ions in a linear structure have the average charges greater than the middle-position ion. These experimental results are well supported by a recent theory on the cluster average charge.