S. Ninomiya et al., STABILIZED HOLLOW ATOMS (IONS) PRODUCED WITH SLOW MULTIPLY-CHARGED IONS PASSED THROUGH METALLIC MICROCAPILLARIES, Physica scripta. T, T73, 1997, pp. 316-317
X-rays emitted from projectiles, such as N6+ and Ne9+, downstream of a
Ni microcapillary target were observed. Appreciable fractions of ions
were found as hollow atoms (ions) with lifetimes of similar to ns.