A particle optical apparatus, such as an ion implantation apparatus, an Auger electron spectrometer, an XPS analysis apparatus, and the like, is provided with a radiation source by means of which a wafer or substrate brought into the apparatus can be bombarded by radiation providing for at least a positively charged surface layer of the wafer or substrate. The apparatus further comprises a charge neutralization device with means for providing secondary electron emission and transport means for transporting secondary electrons. This transport means device is provided with a hollow insulating structure for controlled electron transport based on secondary electron emission, particularly in the form of an electron fibre with electrodes at the entrance and exit. The exit of the electron fibre forms a clean secondary electron source.