Formation of ion clusters by low-energy electrons in nanometric targets: experiment and Monte Carlo simulation.

The first experimental data on the distribution of ionisation cluster size produced by low energy electrons in a target cylinder of nitrogen, 3.5 nm in diameter at unit density, which is equivalent to approximately 2 nm in liquid water are presented. In the experiment, nanometric targets were simulated in the so-called Jet Counter. It consists of a pulse-operated valve which injects an expanding jet of nitrogen into an interaction chamber where a cylindrical sensitive volume is created. This sensitive volume was irradiated by electrons at 300 eV, 500 eV and 1 keV, emitted by an electron gun. The distribution of ionisation cluster size was measured using the single-ion-counting method and compared with the results of Monte Carlo simulation.